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thesis entitled
HABITATS OF THREATENED SMALL MAMMALS ON THE
ROSE LAKE WILDLIFE RESEARCH AREA, CLINTON COUNTY,
MICHIGAN--EARLY FORTIES AND LATE SEVENIIES
presented by
Jacquelyn L. Shier
has been accepted towards fulï¬llment
of the requirements for
M. S. degree in Zoology
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Major professor
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Michigan State
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HABITATS OF THREATENED SMALL MAMMALS ON THE
ROSE LAKE WILDLIFE RESEARCH AREA, CLINTON
COUNTY, MICHIGAN--EARLY FORTIES AND
LATE SEVENTIES
By
Jacquelyn L. Shier
A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Zoology-T
l981
ABSTRACT
HABITATS 0F THREATENED SMALL MAMMALS ON THE
ROSE LAKE WILDLIFE RESEARCH AREA, CLINTON
COUNTY, MICHIGAN--EARLY FORTIES AND
LATE SEVENTIES
By
Jacquelyn L. Shier
In view of succession on the agricultural and forested lands
of a game area in southern Michigan a follow-up investigation was
conducted to determine the differences in composition and distribution
within habitats between current small mammal populations and those
obtained in the 19405, particularly for three threatened species.
Transition from farm-game to wildlife management removed land
from agricultural use. Habitat management continues with shrub strip
planting, food patches, and brushpiles. Farmed areas have reverted
to persistent brome grass (Bromus inermis), Oldfield situations.
Introduced grasses, low plant diversity, and inappropriate
vegetative structure within the oldfields are cited as responsible for
the apparent absence of least shrews (Cryptotis parva) and avoidance
by southern bog lemmings (Snyaptomys cooperi). Lemmings persist due
to their versatile association with transition habitats. Canopy closure
within woodlands reduced the abundance of ground flora such that wood-
land voles (Microtus pinetorum) apparently no longer inhabit the study
area .
ACKNOWLEDGMENTS
I wish to thank Sylvia Taylor, director of the Michigan
Endangered Species Program, for making this study possible; and to
John Lerg who helped in many ways with administration of the grant
that financed this investigation. Other personnel of the Wildlife
Division and particularly members of the Rose Lake Staff were helpful
in many ways.
Assistance in trapping was given by Kevin Jay in 1978, Pete
Verbanac and Brent Danielson in 1979, and Kimberly Rizzo in 1980. I
am grateful to have had free access to the results of other small
mammal studies conducted on the Rose Lake Wildlife Research Area by
Christopher Carmichael in 1978 and by Brent Danielson in 1979. John
Johnson of Michigan State University generously loaned traps for
predator control during the study.
Special thanks to Rollin H. Baker fbr conceiving of this
project and fbr encouragement and guidance throughout. Chris
Faulkner generously contributed to all facets of this study.
This project was supported by federal aid, the United States
Fish and Wildlife Service and the Michigan Department of Natural
Resources cooperating through the Federal Endangered Species Act of
1973 and the Michigan Endangered Species Act of 1974.
ii
LIST OF TABLES
LIST OF FIGURES
INTRODUCTION
Background
Objectives .
METHODS OF STUDY
Small Mammal Survey .
Questionnaire .
Vegetation Surveys
STUDY AREA .
RESULTS AND DISCUSSION .
Croplands
TABLE OF CONTENTS
Annual Grass and Weed Associations .
Perennial Grass and Weed Associations .
Perennial Grasslands
Mixed Perennials and Shrub Association
Intolerant Trees, Shrubs, and Grass Patches :
Mid—Tolerant Woodlands .
Wetlands
SPECIES ACCOUNTS
Cryptotis parva
Microtus pinetorum
Synaptomys cooperi
SUMMARY .
RECOMMENDATIONS
APPENDIX
BIBLIOGRAPHY
Page
iv
vi
Table
10.
ll.
12.
LIST OF TABLES
Monthly and annual mean temperatures recorded at East
Lansing, Michigan (°F)
Monthly and annual precipitation recorded at East
Lansing, Michigan (in inches) .
Comparison of percent land use in the central 325-
hectare unit under intensive study . .
Overall small mammal captures on the Rose Lake Wildlife
Research Area from 1940 to 1946. Totals include all
methods . . . . . . . .
Overall small mammal captures on the Rose Lake Wildlife
Research Area from 1978 to 1980. Totals include all
methods . . . . . . . . . . . .
Importance values of plants in perennial grass and weed
associations in the central study area, 1979 . .
Prey items identified from owl pellets collected on the
Rose Lake Wildlife Research Area from February 24 to
April 1, 1980 . . .
Dates of collection by hand of Cryptotis parva.
Entries are taken from the literature
Dates of trap capture of Cryptotis parva. Entries
are taken from the literature .
Dates of collection of pellets containing Cryptotis.
parva . .
Synaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the years
1979 to l980--P1anted Conifer Stand-A . . .
Synaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the years
1979 to l980--Planted Conifer Stand-B . . . .
iv
Page
15
I6
20
22
25
34
65
66
68
69
77
78
Table Page
13. Synaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the years
1979 to l980--P1anted Conifer Stand-C . . . . . . 79
l4. Synaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the years
1979 to l980--Conifer Hedgerow A . . . . . . . . 80
15. Synaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the
years 1979 to 1980—-Conifer Hedgerow B . . . . . . 81
16. Population changes for resident microtines over three
years . . . . . . . . . . . . . . . . . 85
17. Population levels in Synaptomys cooperi in two Michigan
Counties . . . . . . . . . . . . . . . . 86
LIST OF FIGURES
Figure Page
1. Vegetative cover map for the Rose Lake Wildlife Research
Area in 1970 . . . . . . . . . . . . . . . ll
2. Vegetative cover map for the central 325 hectares . . 12
vi
INTRODUCTION
Background
A major study of small mammals and their habitats in the mixed
agricultural and forested lands at Rose Lake Wildlife Research Area
(hereafter called the Rose Lake Area) was conducted in the early
19405 by joint investigators from the Michigan Department of Conser-
vation (DNR) and Michigan State College (MSU), with published results
by Joseph Linduska (1950) appearing in bulletin form. These threat-
ened small mammals, the least shrew (Cryptotis parva), the southern
bog lemming (Synaptomyscooperi), and woodland vole (Microtus pjne-
torum),(Jones,_gt_al., 1979), were among the small insectivores and
rodents found as members of the local mammalian communities. Periodic
observations of small mammals on the Rose Lake Area in the past
fifteen years have shown no captures or other evidence of the pres-
ence of the least shrew or the woodland vole, and only an occasional
record of the bog lemming. There has been no concerted and system-
atic attempt to appraise or monitor small mammals at Rose Lake since
the mid-19405, especially in view of successional changes in habitats.
This project was, therefore, of great importance to the long-term
research objectives of the DNR. Evidence concerning the reasons why
these small mammals formerly seemingly common and/or widespread are
now rare and/or restricted, might be revealed.
Objectives
It was proposed that a survey of small mammals on the Rose
Lake Area be conducted systematically to determine (a) the kinds,
distributions, habitat preferences, and relative abundance of the
small mammals found there currently; (b) the differences in species
composition between current mammalian populations and those obtained
by the Linduska study in the early 19405; (c) reasons for the apparent
suppressed state or likely disappearance of species on the threatened
list; and (d) a plan to monitor small mammals in selected sites at
Rose Lake in the future so as to maintain basic ecologic and demo-
graphic data on the threatened species.
METHODS OF STUDY
Small Mammal Survey
One objective of this study was to measure the comparative
numbers ofsmall mammals in the several habitats at various times of
the year, and compare them to species diversity and population levels
observed in the 19405 study.
True censuses of small mammals usually require intensive
live-trapping on quadrats or assessment lines several acres in size
(Dice, 1938; Blair, 1941; Stickel, 1946a; and Smith, et_al,, 1971).
For various reasons, these types of procedures were not adopted in
the earlier study by Linduska (1950). Instead, he found it desirable
to sample concurrently in more situations than could be trapped con-
veniently by intensive means. The approach he adopted was one of
live-trapping along lines of measured length as suggested by Dice
(1938) and used by Blair (1939). For the most meaningful comparison,
the same methodology was used in this present follow-up study.
In the earlier fieldwork, trapline placement was systematic
and record keeping thorough, making it possible for the subsequent
investigators to relocate every trapline. Unless otherwise indicated,
all population indices were obtained by using a series of 25 traps
spaced at 7-meter (22-foot) intervals along a straight line 170
meters (8 chains) long. Traplines extended from the field border
toward the center and were located midway between the field edges
3
paralleling the line of traps. Fields larger than 10 hectares (25
acres) received two lines of traps, each was placed 40 meters (two
chains) in from the field border which the lines paralleled. A few
very long hedgerows received 50 traps when it was important to sample
along their entire lengths.
When sampling situations demanded the use of more, or less,
than 25 traps in a line, the capture results have been standardized
to a 25-trap equivalent for their inclusion in Tables 4 and 5.
It was desirable to use the same treadle-operated pressed
fiberboard live traps (4.5 x 4.5 x 16 cm) employed by Linduska in the
19405 study. Unfortunately, they had been discarded years ago when
they became water damaged. Instead, a treadle-operated galvanized-
steel live trap (6 x 9 x 27 cm) made by Leathers and Sons of Athens,
Georgia, was used. Treadles could be adjusted to where traps were
sufficiently sensitive to capture 8- to lO-gram animals.
A few traplines were established in each habitat type (crop-
land, perennial grasslands, hedgerow, and woodlot) examined by
Linduska in the 19405. These were used to determine seasonal abun-
dance and habitat preferences of all members of the small mammal
community in light of successional changes and present land-use
practices. These lines were operated for single three-night sessions
in the fall of 1978, spring and fall of 1979, and in the spring of
1980.
Traps were baited in late afternoon and checked and closed
the following morning, for each of three successive nights of trap-
ping. Those on shaded lines were also operated during the day to
increase the capture rate for Synaptomys and Microtus. A dry bait
combination of peanut butter and rolled oats was used in most situa-
tions. The data recorded upon capturing an animal included its toe-
clipped number, species, sex, reproductive condition, weight,
location on the trapline, and the date. Reproductive condition was
assessed in the manner described by Krebs (1966). For males, the
position of the testes, whether scrotal or abdominal, was noted. For
females, a combination of measures indicated the onset of reproductive
activity in subadults and the stage of pregnancy in adults. These
include the condition of the vagina, whether perforate or not, the
size of the nipples and the surrounding subcutaneous lactation tissue,
as well as degree of protrusion of the abdominal area. The degree
of separation in the pubic symphysis gave evidence of recent par-
turition (Hall and Newton, 1946). Although effective for microtines,
deermice, and jumping mice, these measures were useful for shrews
only in the most advanced stages of pregnancy or lactation.
Since the major objective of this study was to determine the
reasons for the apparent suppressed state or likely disappearance of
the three "threatened" species of small mammals, the least shrew,
the woodland vole, and the southern bog lemming, decidedly different
procedures were employed in the search for these species in areas
other than those surveyed by Linduska.
Additional study sites having properties similar to those
reported in the literature for these three species were selected for
trapping using less conventional methods. Removal-trapping with
Museum Special snap traps were employed for the purpose of catching
"rarer" species not especially evident until the removal of the more
"dominant" mammals which may initially monopolize trap sites. Pit-
fall can-traps set alone and along drift fences were used to search
for all three of the species. These sets were put into operation
when low population levels the first year gave the impression that
animals might be avoiding the conventional live and snap traps. Both
Microtus and Synaptomys are reported to frequently avoid the latter
(Bailey, 1929; Jackson, 1961; and Master, 1978). When the trapping
success for Synaptomys with both snap and live traps improved in
1979 the can-traps were abandoned, since the yield from these proved
to be lower in upland situations than with the standard traps.
Examination of the 19405 trapping records and past litera-
ture on Synaptomys suggested that dispersing individuals of this
species may be captured almost anywhere with intensive trapping
effort. However, concentrations were more often reported from bogs,
riparian habitats, and upland in moist-mid-successional stages having
monocotyledonous vegetation. In these situations Synaptomys was
searched for, initially with snap traps. If an individual was cap-
tured within the three- to six-day search period, the snap traps
were replaced with live traps for additional investigation. In one
pine plantation where a colony of 16 to 20 animals was located, an
exhaustive analysis of their use of this habitat was performed to
aid in predicting the presence of the lemming at other sites on the
Research Area. Runway systems were excavated to locate food caches,
nesting sites, and latrines, and to determine what locations within
the grove were most heavily used. Traps for Synaptomys were vari-
ously baited with apple and/or grass (after Burt, 1928) and with the
peanut butter and rolled oats combination as used for the general
trapping.
The woodland vole was searched for by trapping in underground
runways located in the humus layer of area woodlots, orchard remnants,
and hedgerows of ornamental shrubs. Four woodlots were selected on
the basis of herbaceous ground-layer vegetation and humus proper-
ties. Those with deep, mgr humus (Jameson, 1949) and an abundance
of herbs with tuberous root systems that would provide food and cover
for the woodland vole (Paul, 1970) were more likely to support breed-
ing populations of the species. Runways were then located and a
portion large enough to accommodate a Museum Special snap trap was
excavated and set with a trap, as suggested by Paul (1970). Paul
also advised that these sets be covered over to block out light.
Eadie (1936) and Miller (1964) found that it made little difference
in the capture success. Here, initial trapping with the set covered
over had little effect on what species were captured, or whether soil
excavation by animals during the night covered the traps, so they
were left uncovered in subsequent settings.
A special search had to be made for Cryptotis since 3- to
4-gram shrews are too light to consistently trip the treadles of the
large live traps and too short to be caught by Museum Special snap
traps from the front. The least shrew is frequently reported to have
been found beneath logs, boards, and other debris in fields of
herbaceous plants or in pastures (Moseley, 1930; McCarley, 1959).
Whenever such items were found on the Rose Lake Area, they were
examined carefully for these animals or any leaf nests or runways
of pencil diameter that would suggest their presence in the area.
Fifty pieces of aluminum sheeting measuring 1 x 2 meters were also
laid out in several fields having properties similar to those reported
by Howell (1954) and Getz (1962) in the hope of attracting these
shrews. Examination of these sheets for nests and runways was made
periodically from August 1979 to June 1980. Mouse traps were set
around the edge of those sheets where sign suggested the possible
presence of the least shrew.
Questionnaire
A questionnaire was mailed to field mammalogists within the
range of the southern bog lemming to collect recently gathered
information on the species' local habitat use and small mammal
associates (see Appendix). A comparison between pepulations in Michi-
gan and those in other regions where the lemming appears to be thriv-
ing will aid in determining why the species is apparently threatened
in Michigan.
Vegetation Surveys
Vegetation types on the Rose Lake Area for the years 1941
to 1946 were accurately determined by combining references from
several sources. Brief descriptions on the trap cards by Linduska
provided a species list of plants present on the site and a vague
idea of habitat fine structure for each of the areas he trapped.
A more complete picture of habitat structure for these areas was
obtained from camera point photographs periodically taken of the
area from 1938 to 1960 by Rose Lake area personnel. Photographs
also helped to characterize the earlier vegetative cover present on
areas sampled in this study which had not been trapped in the 19405.
Although the latter information was not crucial to this follow-up
investigation, it helped to place the results of this recent study in
better perspective. In addition, the Rose Lake Station files con-
tained photographs of numerous management activities occurring on the
area throughout the years, and of their subsequent effects on the
habitat. Finally, personnel employed by the Station over the years
were consulted for details not available from the above sources.
Thorough description of the habitat was made for each of the
traplines run in this recent survey. Plant species were identified
according to Gleason and Cronquist (1963). Photographs were taken
of noteworthy situations. In addition, a photographic record was
systematically made of those portions of the area where trapping
occurred, most of which correspond to regions in which the original
study was conducted. Systematically recording the remainder of the
Rose Lake Area on film would have been a major undertaking of
limited value, as most of it has grown up to a thick tangle of shrub
and understory trees. These photographs have been accessioned into
the film file located at the Rose Lake Wildlife Research Station,
8562 E. Stoll Road, Bath Township, Clinton County.
10
Vegetative cover maps for the Rose Lake Wildlife Research
Area in 1970 and the central 325 hectares (800 acres) where most
of the trapping occurred are shown in Figure l and Figure 2,
respectively.
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COVER LEGEND
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Upland Brush [:1 Follow Fields and Grass Areas
Lowland Woods °—°—°- Brush and Shrub Planting- Narrow
Lowland Brush Evergreen Planiinqs
m Marsh 5 a a Slump Piles or Rows
Figure 2.--Vegetative cover map for the central 325 hectares.
STUDY AREA
The Rose Lake Wildlife Research Area comprises 1350 ha (3,334
ac) (rf state-owned mixed agricultural land, forests, and wetlands
in Bath Township, Clinton County and Woodhull Township, Shiawassee
County, Michigan (see Figure l). The study area was included in the
initial purchase of land for the Research Area by the DNR in 1938.
Topography varies between comparatively level and rolling
countryside. The steepest slopes are wooded in most cases, but in
the late 18005 early settlers cleared much of the rolling terrain
for agriculture; subsequently, it became badly eroded. Early efforts
(in the late 19305) by personnel at the Rose Lake Wildlife Research
Station to stabilize those areas prone to erosion with shrub plant-
ings have not only stopped the erosion, but accelerated the return
of many areas to a wooded condition. The sandy, less productive
soils were removed from production while farming was continued on
the better soils (Rose Lake Wildlife Experiment Station, 1941).
The amount of farming activity on the area has continued to
decrease. Less than 40 ha (99 ac) are currently farmed by share-
croppers and Rose Lake personnel.
Before the land was cleared, the uplands were covered by
beech (Fagys grandifolia), maple (Acer spp.), hickory (Carya 5pp.),
and oak (Quercus 5pp.) forests with a few scattered white pines
13
l4
(Pinus strobus). Lowland forests were dominated by maple, ash
(Fraxinus spp.), and tamarack (Larix laricina).
The soil pattern is complex as is characteristic of heavily
glaciated areas where there is a wide variation in drainage condi-
tions. Twenty-seven soil types were recorded for the Area in the
19405. In the well-drained uplands were Newaygo loam, Bellefontaine
sandy loam, and Coloma loamy sand. The poorly drained soils of
kettle-holes, marshes, and lake and stream bottoms were predominantly
Rifle and Greenwood peats, and Kerston and Arlisle mucks.
A slightly different soil profile was reported for the 19805.
Well-drained soils include Boyer sandy loam, Marlette loam, and
Spinks loamy sand. The poorly drained soils include Adrian muck,
Carlisle muck, Gilford sandy loam, Houghton muck, Tawas muck, and
Wasepi sandy loam (Threlkeld and Feenstra, 1974; and Pregitzer,
1978).
Mean winter (October-March) temperature is 0.4°C (32.7°F)
while mean summer (April-September) temperature is 16.7°C (62.1°F).
Periods of extremely hot or cold weather are usually of short dura-
tion. Precipitation averages 87.5 cm (34.4 in) per year. The pre-
vailing winds are from the west with an average speed of 16.6 km/hr
(10.3 mi/hr) (U.S. Weather Bureau, pers. comm.).
Details of meteorological conditions during both periods of
investigation are given in Tables 1 and 2. During the 19405 study
period, both snow and rainfall were above normal.
For the recent study period, annual precipitation was 4 to 5
inches below the normal 31.6 inches, despite heavy snowstorms in
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17
January of both 1978 and 1979. The winter of 1980 had conditions
which may have proven detrimental to the local small mammal popula-
tions. Of the 9 inches of winter precipitation, 33 percent was in
the form of rain. Although the remaining 67 percent was in the form
of snow, the accumulation never exceeded more than three inches or
lasted longer than 5 days. These snow conditions provided poor
insulation of the litter layer from cold winter temperatures. Con-
sequently, frequent freezing and thawing of the water-saturated
litter layer probably occurred, critically stressing the more sensi-
tive microtines, including the bog lemmings.
RESULTS AND DISCUSSION
The approach taken here was to determine the more important
changes characteristic of plant succession on the area and to take
some measurements of their effect on certain of the resident small
mammal species.
Direct measurements of the effect of succession were obtained
in two ways. One was to determine the effect of the changes in terms
of the habitat requirements of each species. This method is closely
applicable only when the food and cover requirements have been worked
out in detail. This has been done for most of the small mammal
species resident on the area, through the use of published ecologi-
cal accounts, but only to a limited extent for the woodland vole and
'the least shrew. The other method used was to analyze the cover
(occupied by each species in the present and in the earlier study and
‘relate this to the more important vegetative changes that have taken
place in the meantime.
To determine whether certain habitat conditions have become
"KDre or less productive for certain small mammals in the past 35
years, the principles indicated above were applied to the changes in
Cover which have occurred.
In the early 19405 a farming program was set up under the
Qtridance of the U.S. Soil Conservation Service and Michigan State
18
19
College (now Michigan State University). A 280-hectare livestock
farm employing new land-use practices was put into Operation. Crap
rotation, contour farming, level ditching, flooding, fence row
development and woodlot management were practiced to enhance pro-
ductivity of both crops and wildlife.
Management activities on the Area provided a great diversity
of habitats for small mammals. Of the 475 hectares (1,172 acres)
in ownership by 1940, cropland and pastureland comprised 64 percent
of the total area; wetlands constituted 24 percent; and woodlots
made up 12 percent (Table 3). In the 325-hectare portion of most
intensive study about 71 percent of the land was in pasture and
crops; 16 percent in wetlands; and 13 percent was in woodlots. These
land-use percentages were typical of the private farms in the imme—
diate area.
The changes that each vegetation type has undergone during the
35 years between observations at Rose Lake are presented in a dis-
cussion format. Results of the various trapping operations have been
arranged in tabular form and are referred to in the discussion when
appropriate. An overall perspective on the fate of the three
threatened species of small mammals is presented in the form of
species accounts following the general discussion.
Croplands
The adventive vegetation in cultivated fields is sparse and
consists chiefly of annuals and biennials. Relatively large areas of
bare soil are present between the individual plants.
20
TABLE 3.--Comparison of percent land use in the central 325-hectare
unit under intensive study
19405 19705
Uplands
Croplands 19.2 5.6
Annual grasses and weeds 9.4 0.6
Perennial grasses and weeds 23.9 43.0
Mixed perennials and shrubs 18.3 1.0
Intolerant trees/shrubs 2.9 11.6
and grass patches
Mid-tolerant trees and shrubs 10.2 25,0
Tolerant trees 0.0 0.0
Wetlands
Grass-sedge marshes 6.5 1.7
m
Wooded Swamps 4.0 10.
21
Forties
Farming of the area was diversified, with fields supporting
two crops having different maturation times. Crop rotation occurred
on all but the few mucklands. In addition, strip-cropping was used
on the largest fields. Corn, oats, and wheat were the principle cash
crops grown; and alfalfa and red clover were grown for hay produc-
tion. Straw was spread over some of the fields planted with crops
to reduce erosion of the topsoil. This latter practice no doubt
also increased the number of weed seeds in the seed pool in these
areas.
Land devoted to the growing of cash crops such as corn,
wheat, rye, and oats at this time comprised 19.2 percent of the
central study area.
In 1950 the EurOpean smooth brome grass (Bromus inermis) was
added to hayfields.
During the summer and early fall months the prairie deer-
mouse (Peromyscus maniculatus bairdi) was the dominant small mammal
species in cropland habitats (see Table 4). Traplines set in all
crop types caught an average of 2.8 individuals per three-day session.
The only other small mammal to be taken regularly was the introduced
house mouse (Mus musculus), with an average of 0.37 individuals per
line.
From December to March the meadow vole (Microtus pennsylvani-
ggs) was the most common associate of the prairie deermouse in crop-
land. In those situations providing an abundant ground cover it
TABLE 4.--0verall small mammal captures on the
Totals include all methods
22
Rose
Lake Wildlife Research Area from 1940 to 1946.
m
a
.3 'g m 3 3 Percent
13 a: g> S a; I; 3 «a Land-
'— 3
xesugmra o 3.5- ; â€5e
teases“. s 2%.»;
.9... a: 5‘†m8 .2“ a .2.= ele
Uplands
Crapland No. of
(106 lines) Individuals 0 0 7 0 11 301 0 40 19.2
No. per
Trapline O 0 0.07 0 0.10 2.8 0 0.37
Annual grasses No. of
and weeds Individuals 0 0 22 0 0 77 0 17 9.4
(24 lines)
No. of
Traplines 0 0 0.90 0 0 3.36 0 0.70
Perennial grasses No. of
and weeds Individuals 0 2 5 1 0 7 0 1 20.0
(8 lines)
No. of
Trapline 0 0.25 0.63 0.13 0 0.88 0 0.13
Perennial grasses No. of
(6 lines) Individuals 0 1 5 0 0 18 O 2 3.9
No. of
Traplines O 0.16 0.85 0 0 3.0 0 0.3
Mixed perennials No. of
and shrubs Individuals 3 17 27 20 7 32 0 6 18.3
(22 lines)
No. of
Trapline 0.13 0.76 1.21 0.89 0.31 1.43 0 0.27
Intolerant No. of
Trees/shrubs Individuals 0 3 O O 5 0 0 0 2.9
rass patches
7 lines) No. of
Trapline 0 0.43 0 0 0.75 0 0 0
Mid-tolerant No. of
trees/shrubs Individuals 0 52 0 2 142 0 O 2 10.2
(44 lines)
No. of
Traplines 0 1.18 0 0.05 3.22 O 0 1.0
Wetlands
Grass-sedge No. of
marshes Individuals 3 0 4 0 0 0 0 0 6.5
(3 lines)
No. per
Trapline 1.0 0 1.3 0 0 0 0 0
23
greatly outnumbered the deermouse. In contrast, fields where corn
was stored as shocks during the winter were favored as'winter refuge
by most of the local small mammals, including the three species that
are presently considered threatened. Linduska (1950) actually found
as many individuals of these latter three species in one winter by
censusing under corn shocks as he did in all his years of trapping.
Seventies
Of the land previously used for the growing of grains, 70
percent was retired from cultivation by the late 19605. Since then,
these lands have advanced to the perennial grass and weed stage.
The 30 percent remaining is planted only with corn on a share crop
basis for a program which provides for 25 percent of the crop to be
left standing for wildlife food and cover. Annuals and biennials
thrive between the rows of corn. When these fields are left fallow,
even for one season, the foxtails (Setaria 5pp.), pokeweed
(Phytolacca americana), and Lamb's quarters (Chenopodium album)
invade the field en masse.
Today, corn shocking is no longer practiced. Instead, the
whole stalk is cut and removed from the field in the fall for silage.
In addition, only a small portion of each field of corn is left
standing over the winter for wildlife. Such a practice may still
allow mice to feed on the fruit in winter, however, its value as
cover when standing, compared to when it is in shocks, is greatly
reduced. This fact alone probably diminishes the value of cornfields
to small mammals in winter compared to what it was in the forties.
24
In this recent investigation only prairie deermice were cap-
tured in croplands during the winter. This evidence, although
gathered from a limited amount of winter trapping in January 1979,
indicates that cornfields harvested by modern methods may not provide
sufficient cover for meadow voles or the rest of the local small
mammals as they did in Linduska's day. This also means that winter
censusing for any of the threatened small mammals should now be
conducted in other suitable cover types, rather than in cornfields.
The principal species in croplands today are still the
prairie deermouse and the house mouse (see Table 5). An average
catch of 3.8 deermice and 0.77 house mice per trapline was obtained.
Since the prairie deermouse is a species which often shows distinct
fluctuations in population levels over a period of years (Blair,
1940; Linduska, 1950; and Terman, 1966), this figure in no way indi-
cates the presence of a higher mean population level than existed in
the forties. In fact, Linduska observed a marked increase in live
trap catches in each succeeding year of study. This trend started
with a low of 0.6 individuals per trapline in July 1940 and ended
with a high of 4.3 per line in March 1946. Although no data were
reported for 1943 to 1945, Station records show that eight lines
set in craplands in 1944 caught an average of 3.9 individuals per
line. Since this value lies between those found for 1942 and 1946,
it gives credibility to the uniform increase inferred by his graph,
rather than a crash, during the intervening years.
Trapping during the fall of 1978 in cornfields yielded a
catch of 5.6 prairie deermice per line. By the following April a
25
TABLE 5.--Overall small mammal captures on the Rose Lake Wildlife Research Area from 1978 to 1980.
Totals include all methods
is
U
a E m Percent
s .‘23 s: s 35 3 s m"
a; so u a: TE .- Use
all; 1:; 8F: 8 §8 §E 3
LC ‘0) U: 0 3 mm
8'6 3* s as 8‘†5‘4 3|:
Uplands
Cropland No. of
(21 lines) Individuals 0 1 l 0 0 58 0 10 5.6%
No. per
Trapline O 0.04 0.04 0 0 3.8 0 0.77
Annual grasses No. of
and weeds Individuals -- -- -- -- -- * * * 0.18%
(sightings‘)
No. per
Trapline
Perennial grasses No. of
and weeds Individuals 2 64 391 0 16 26 52 3 14.5%
(36 lines)
No. per
Trapline 0.05 4.8 22.4 0 0.44 0.85 3.94 0.07
Perennial rasses No. of
(389 lines? Individuals 3 273 553 0 101 13 91 1 28.5%
No. per
Trapline 0.05 1.10 6.85 0 0.42 0.37 0.77 0.08
Mixed perennials No. of
and shrubs Individuals 0 5 5 0 9 4 1 0 1.0%
(4 lines)
No. per
Trapline 0 0.87 0.4 0 2.25 0.6 0.25 0
Intolerant No. of
Trees/shrubs Individuals 11 71 102 6 73 3 14 0 11.6%
rass patches
I15 lines) No. per
Trapline 0.42 1.58 2.23 0.21 1.83 0.09 0.59 0
Mid-tolerant No. of
trees/shrubs Individuals 6 45 7 19 72 5 8 0 26-0%
(50 lines)
No. per
Wetlands Trapline 0.12 0.90 0.14 0.38 1.44 0.10 0.16 0
Grass-sedge No. of
marshes Individuals 24 0 129 0 3 0 10 0 12.2%
(28 lines)
N0. per
Trapline 1.81 0 4.82 0 0.04 0 0.93 0
26
catch of 0.82 per line, compared to the 3.6 obtained by Linduska in
March of 1944, gave every indication that a crash in their population
level had occurred. However, the population in cr0p1ands had
increased to 6.3 individuals per trapline by June. Apparently, the
cornfields are somewhat inhospitable to deermice during the wet
spring when the fields are saturated with meltwater. It is probable
that the summer population consisted of individuals which had dis-
persed into the cornfields after they had dried out a bit.
There was no sharecropping on the Rose Lake Area in 1980.
Only a few small corn patches were planted by station personnel that
spring. Should this trend continue, it will probably have little
direct effect on the three threatened species of small mammals under
consideration here, since cornfields were of fairly limited value to
these species by 1980. Their movements into corn shocks in the winter
of 1941 is viewed as having been a preferential act engaged in by
these animals, rather than a necessary one stemming from any lack of
sufficient cover in their summer range or in alternative ranges.
Annual Grass and Weed Associations
First-year hayfields of alfalfa and red clover, and grain
fields in the late fall period (cornfields more than other grains),
are similar in many respects to the annual grass and weed stage in
succession from plowed ground which Allen (1938) describes. What is
bare ground in spring closes in quickly by summer with the matura-
tion of cultivated plants and weed species. Consequently, classifi-
cation of cover type relative to what is significant to the small
27
mammal community is complicated by drastic seasonal changes in the
habitat. For the purpose of tabulating data in Tables 4 and 5,
percent land-use was based exclusively on spring cover maps. However,
the assignment of individual traplines to the various seral stages
was determined by the condition of existing cover each time the
trapline was operated.
Forties
Newly planted hayfields, cornfields in the fall, and retired
croplands contributed to the annual grass and weed cover type in the
19405. At that time, hay production and crop rotation placed an
average of 30 hectares per year into this early stage of succession.
Most of these autumn cornfields were occupied by common ragweed
(Ambrosia artemisifolia), yellow and green foxtails (Setaria glauca
and S. viridis), lamb's quarters, knotweed (Polygonum aviculare),
and in lesser numbers by other annuals. By the following spring the
dominant vegetation in these same cornfields consisted of early—stage
perennial grasses and weeds such as quack grass (Agropyron repens),
broom sedge (Andropogon virginicus), and wormwood (Artemisia
campestris), red sorrel (Rumex Acetosella) and pokeweed.
Seventies
Because of limited tilling or use of herbicides during the
present investigation, annual grass and weed associations developed
within the cornfields. The plant species diversity closely matched
that described by Linduska (1950) for the forties. Sampling for
small mammals occurred here in the fall of each year.
28
Also supporting annual grasses and weeds were strips of land
10 meters wide by 100 to 1000 meters long that were plowed for the
planting of shrub hedgerows along the roadways in 1978. Subsequent
colonization by annual grass and weed species,gradually increased
the cover available. By 1980 these strips were being taken over by
perennial grasses and weeds.
Now, as in the 19405, these recently disturbed upland habitats
appear to support only the prairie deermouse and the house mouse,
and infrequently, the meadow jumping mouse (Zapus hudsonius). In
late fall after harvest and in spring before maturation of the planted
species only the prairie deermouse inhabitats open farmland. Accom-
panying the summer transition in abundance of cover there is an
influx of the house mouse into croplands when adequate shelter
becomes available. Both Linduska (1950) and Whitaker (1967) docu-
mented these moves by house mice, and they were observed again in
this follow-up survey. In fact, 22 of the 57 house mice captured
by Linduska in cr0plands and annual grass and weed associations were
taken after August 1 when the ground cover had matured, and all were
captured after July 8. Likewise, the ten house mice captured in the
seventies from cornfields were taken after July 24.
Although these annual grass and weed associations support a
modest growth of monocotyledonous vegetation and some species of
arthropods, they are unlikely fall and winter refugia for either the
least shrew, the southern bog lemming, or the woodland vole.
The woodland vole has only been reported from such situations
when tuberous root crops are present (Linduska, 1950; Paul, 1970).
29
There is not enough litter accumulated or high enough stem density
for either the bog lemming or the more common meadow vole to estab-
lish the runways they usually construct to move, under cover, between
foraging sites and nests. Whether they forage here to any extent
in the winter was not determined in this present investigation.
However, Linduska (1942a) did observe a significant movement of voles
into cornfields once appropriate cover existed in the form of field-
shocked corn and a moderate accumulation of snow. During the spring,
summer, and early fall, he caught only 7 meadow voles from 106 trap-
lines (an average of 0.07 voles per line), and no bog lemmings or
woodland voles, in unaltered cornfields. By January a seven-day
session of removing rodents from 28 acres of field-shocked corn
yielded 166 voles (the equivalent of 0.8 voles per line), several
woodland voles, and a few Synaptomys. And there was not enough
litter or debris accumulated in these recently disturbed fields for
the least shrew to build nests in such "stable" sites as seem to be
preferred by this species (Whitaker, 1974).
Perennial Grass and Weed Associations
The transient annual-biennial stage on both cultivated and
small grain lands is followed by a longer period in which perennial
grasses and weeds predominate. This usually begins about three years
after abandonment. Canada bluegrass (Poa compressa) and Kentucky
bluegrass (Poa pratensis) are of particular importance in southern
Ml°¢higan. Either one or both of these species may completely cover
the .surface of the ground over large areas; Canada bluegrass is
30
likely to occur on the heavier soil types, whereas Kentucky bluegrass
tends to be more common on the lighter upland soils. Many of the
weedy associates have long tap roots that allow them to co-exist
with the grasses which use mainly the upper soil levels.
Forties
In 1940, 20 percent of the central area was maintained as a
perennial grass and weed association for the pasturing of a dairy
herd. The dominant grass species were Canada bluegrass and Kentucky
bluegrass, the latter was referred to as June grass in notes by
Linduska. Considerable variation existed between fields with respect
to species diversity and abundance of the herbaceous types mixed with
these grasses. Among them were goldenrods (Solidago spp.), milk-
weeds (Asclepias spp.), yarrow (Achillea Millefolium), common mullein
(Verbascum Thapsus), sour dock (Rumex crispus), fleabane (Erigeron
ppppg), flowering spurge (Euforbia corollata), and wormwood.
Second- and third-year hayfields are included in this cate-
gory because the associated weeds were perennial and the litter layer
had developed considerably by this time.
Oldfields of this early seral stage contained a slightly
higher diversity of small mammal life than did either the croplands
or annual grasslands (see Table 4). However, the overall density of
small mammals was substantially lower. Linduska captured only 0.88
prairie deermice and 0.63 meadow voles per trapline. The short-
tailed shrew first appears in this seral stage where there is enough
ground litter to provide both cover and abundant food of the types
31
usually selected by the shrew. The diet of the short-tailed shrew in
Indiana consists of 36 percent earthworms, 9 percent slugs and
snails, 8 percent lepidopterous larvae, crickets, centipedes and
beetles (Whitaker, 1972); all of these are more abundant where the
ground litter is substantial, or where a moderate diversity of flower-
ing herbaceous plants occur.
Both the meadow vole and the short-tailed shrew were strictly
fall and winter residents.
Linduska (1950) observed an annual migration in September by
the meadow vole and the southern bog lemming (both from wetlands)
and the woodland vole (from the woodlots) into these upland grass-
lands. Slightly fewer had settled here than had invaded the crop-
lands. Summer trapping failed to take any bog lemmings or woodland
voles, and relatively few meadow voles were captured in these areas
in summer. Yet, from December to February of 1942, both bog lemmings
and meadow voles were common in grasslands. Linduska believed that
microtines avoided these areas in summer because most of the vegeta-
tion was either severely dehydrated or grazed short by the livestock.
When these rodents finally moved upland in the fall, cooler weather
had allowed rehydration of the grasses and there was a considerable
amount of new fall sprouts for food.
The winter of 1942 was the beginning of an upward population
trend for the local bog lemmings which appeared to peak in 1946,
although sparse data from 1943 to 1946 during the war makes this
conclusion tentative. In December of 1942 lemmings were especially
32
numerous in a 1.5 hectare opening beside a stream bottom grown up to
St. John's wort (Hypericum perforatum), dewberry (Rubus hispidus),
wormwood, milkweed,nullein,ragweed, and bluegrass. In this area
during mid-day these animals could be seen running along the snow
surface as they moved between tunnels. Since winter trapping under
snow cover was conducted only within pine hedgerows, cornfields, and
along the edges of vernal ponds, it is unknown whether current peren-
nial grass and weed associations serve as winter refugia for either
the lemming or the woodland vole.
The only locality, other than field-shocked corn in winter,
from which Linduska (1950) reported capturing a least shrew was an
old field-bog margin, on 2 October 1941. Although the site bordered
on an extensive acreage of old field and pastureland, no additional
captures were made during regular trapping operations. Several were
taken later in February from beneath corn shocks only 400 meters from
the bog margin.
Seventies
The abundance of habitat in the perennial grass and weed
association has decreased only slightly, from 20 to 14.5 percent,
over the intervening years. However, major differences in success-
ional stage and plant species composition exist, and are probably
responsible for the dramatic differences seen in the accompanying
small mammal community.
Prior to their abandonment in 1967 when the dairy herd was
sold, hay and pasturelands were subject to a major change in principle
33
grass species. Native bluegrasses were replaced by smooth brome
grass imported from Europe for hay production. The lands presently
in the perennial grass and weed stage derive from lands abandoned
from grain cultivation which were subsequently invaded by brome grass
and herbaceous weed species from the pasturelands.
Free from cultivation for a considerable period of time,
these tracts have reached a more advanced seral stage than had the
perennial grass and weed associations that Linduska had available to
sample. While the weeds were dominant on his frequently cultivated
hay and pasturelands, long-term abandonment of today's grass and
weed fields has allowed a thickening of the sod and the grasses
dominate. Consequently, the weedy associates are different and fewer
in number. The relative importance values of the grass and weed
species found in two abandoned fields in 1979 are shown in Table 6.
When one looks at which cfldfields are inhabited by the brome
grass, it becomes apparent that some prior clearing of the land was
necessary for its successful invasion. Hence, it dominates on the
cultivated portion of the Rose Lake Area. Here it established ini-
tially by direct seeding onto tilled lands, and later it spread to
nearly all lands left fallow.
The more mature perennial grass and weed associations of the
seventies appear to support a more stable small mammal community.
Shrews and microtines are year-round residents and occur in much
greater numbers than in the younger, and drier, grasslands of the
forties (see Table 5). The short-tailed shrew has increased from 0.25
34
TABLE 6.--Importance values of plants in perennial grass and weed
associations in the central study area, 1979
SPECIES Importance Value
Grid A
Bromus inermis 168.27
Lychnis alba 5.96
Daucus carota 5.88
Berteroa incana 5.82
Solidago canadensis 4.96
Xanthium strumarium 3.18
Agropyron repens 2.92
Solidago graminifolia 1.55
Trifolium pratense 1.46
Grid 8
Bromus inermis 128.92
Daucus Carota 22.54
Medicago sativa 11.57
Taraxacum officianale 6.36
Solidago canadensis 5.92
Solidago graminifolia 5.64
Cirsium arvense 5.63
Bertaroa incana 4.52
Agropyron repens 2.69
Lychnis alba 2.64
Xanthium strumarium 1.84
Convolvulus arvensis 1.74
35
to 4.8 individuals per trapline and the meadow vole has increased
from 0.63 to a phenomenal 22.4 mice per line of 25 traps. The meadow
vole still exhibits a multi-annual fluctuation in population density.
Since the value of 22.4 was obtained primarily from trapping in the
fall of 1980 during a p0pulation high, it probably falls well on the
high side of the actual average for the entire study period. More
realistic as an average value is that of 6.8 per line given for
the perennial grasslands.
There has been no significant change in either prairie deer-
moust or house mouse populations in this habitat type. In addition,
the more mature fields of today support a modest 0.44 white-footed
mice.
The apparent increase in meadow jumping mice from none to 3.9
per trapline may be, in part, an artifact of the difference in the
trap type used in the two studies. Linduska (1950) mentions that,
even though only one individual was taken by trapping during the
course of his work, at least a dozen were removed from post holes
that were dug near a marshy area. His livetraps were much smaller
than mine; measuring only 4.5 x 4.5 x 16 cm. It is plausible that a
trap this small might be avoided by the jumping mouse, for they
readily entered the livetraps used here. They also were caught
frequently in snap traps in the present study. However, a comparison
of snap-trapping results for the jumping mouse is not possible since
Linduska's use of these traps was almost exclusively confined to grain
fields where no jumping mice were captured, and to winter grasslands
when these mice would be hibernating.
36
These perennial grass and weed associations are the first
stage in the seral development from cropland to forest where condi-
tions supposedly would be suitable for the least shrew. There is a
great diversity of broad-leaved herbaceous plants and enough stability
of the plant community to support a varied insect diet for the least
shrew. Whitaker and Mumford (1972) examined stomach contents which
primarily included lepidopterous larvae, earthworms, spiders,
orthopterans, and aphids. There also appears to be sufficient sta-
bility in the vegetative structure to provide suitable nest sites,
and there is lodged grass for winter refuge (Davis and Joeris, 1945).
Whether these factors are sufficient to attract the least shrew if it
were presently on the area is unknown. The inferences drawn here
about potential habitat selection, foraging sites, and trappability
mostly derive from publications of minor observations made while the
investigators were engaged in research on other species, and some
come from incidental encounters with the shrew. This wide range of
observations is summarized by Whitaker (1974), but even this large
body of literature does not give us a very clear picture of the
ecology of this species. Consequently, the previous statements about
likelihood of current residency or habitat use by the least shrew on
the Rose Lake Area are a "best guess" based on an overall considera-
tion of this body of data.
37
Perennial Grasslands
Forties
In 1940 only 4 percent of the central area possessed a thick
enough sod ground cover to have excluded those weeds that were pres-
ent in the younger grasslands. These tracts are considered here in
the perennial grassland stage as a midpoint in the seral development
of plowed ground to woodland. These areas were also used for the
pasturing of the dairy herd. Canada bluegrass and Kentucky bluegrass
were the dominant grass species, forming dense uniform stands with
timothy (Phleum pratense).
The principal species of small mammal captured by Linduska
in bluegrass sod were the prairie deermouse, house mouse, and the
meadow vole. In all seasons he took a number equal to that collected
from adjacent croplands (see Table 4) of both the deermouse (3.0
per line) and the house mouse (0.3 per line). Subsequent to the
movement of microtines to upland habitats in the fall, he captured an
average of 0.8 meadow voles per trapline.
Pasturelands and other sod areas were attractive to bog
lemmings as winter refuge, just as some perennial grass and weed
associations sustained winter colonies. In February 1942, 50 snap
traps were operated a total of four nights at the edge of a bluegrass
pasture and 18 lemmings were taken from less than half an acre.
Seventies
All the grasslands retired from pasturing the dairy herd
since the introduction of brome grass onto the Rose Lake Area in 1950
38
eventually became occupied by brome. In comparison to those grass-
lands that were abandoned while under cultivation for hay, these
pastures have had a longer period of time without disturbance to the
sod layer. Hence, today these fields are essentially monotypic, and
very stable in this state of succession. Their lack of plant divers-
ity discourages seed-eating birds and mammals from inhabiting these
fields, and consequently the introduction of propagules from other
plant species is slow. The few associates found with brome grass in
these mature fields were goldenrods and soapwort (Saponaria
officinalis).
The transition of perennial grasslands to a woody condition
is further curtailed by the apparent resistence the growth form of
brome grass has to the germination of other species. Colonization
by woody species occurred in one field only, where the grade was
sufficiently steep to have allowed a mild erosion of the topsoil and
a thinning of the grasses there. Although the sod areas have been
undisturbed by man for at least 15 years, they can be expected to
remain this open for another 15 years, and probably longer (Bump,
1950). In a study similar to this one Bump found that, even though
apen fields were located a short distance from existing seed sources,
colonization was much less rapid on sites that supported a particu-
larly lush growth of grass and other herbs. In his study area,
several such sites remained quite open even though untouched by man
for 30 years or more.
The perennial grass association now occupies 28.5 percent of
the central 325 hectare study area (see Table 5) and was the
39
predominant habitat type during the present investigation. Even more
importantly, the overwhelming success of smooth brome grass has sig-
nificantly altered the patterns of seasonal distribution and abun-
dance in the grassland small-mammal assemblage.
The widespread establishment of monotypic brome grass cover
has substantially reduced the amount of grassland habitat that will
support the prairie deermouse. In the forties, Linduska caught an
average of 3.0 deermice per trapline in bluegrass sod, whereas in the
seventies only 0.37 per line were taken. Closer examination of the
seventies data revealsthat captures of deermice within brome grass-
lands occurred only in early seral stage grasslands directly adjacent
to croplands. Here food was readily available from both the mature
crop plants and from weeds that grew among the rows, and abundant
cover could be had within the grasslands. The discovery of several
occupied deermouse nests within the adjacent brome field verified the
use of grassland for cover in these situations.
While reduced in value to the prairie deermouse, mature
perennial grasslands were more attractive to the meadow vole and the
short-tailed shrew. Linduska obtained an average of only 0.85
meadow voles in the few sod fields that there were to examine,
whereas extensive trapping in the seventies netted an average of 6.8
voles per trapline. With the dramatic population fluctuations
exhibited by this species, trapping results varied from an average
of 1-2 per trapline during a papulation low to a high of 22 or more
per line. More significant is the fact that mature brome grass
40
fields support populations of voles even in the driest years. Granted,
populations also became higher in wetlands when grasslands were very
dry in 1978, but the upland fields always had viable breeding p0pula-
tions, numbering about 20 per hectare. There was no noticeable evi-
dence of an annual upland migration of microtines in the fall like
those that Linduska observed. Or if they did occur, then the grass-
lands are now extensive enough to absorb these individuals into wide-
spread resident population with little effect on local numbers.
Whatever the case may be, the grasslands were not completely aban-
doned during the hot summer. That moisture retention by brome grass
fields is probably greater than in the bluegrass fields in summer,
and therefore, has less affect on annual movements by meadow voles,
was discussed in the section on perennial grass and weed associations.
The greater moisture retention of brome grass cover seems to
have had a different, but equally significant, affect on the short-
tailed shrew. In both brome and weed fields, and in brome alone,
Blarina reached densities far greater (4.8 and 1.1 shrews per trap-
line, respectively) than what had been observed by Linduska for
bluegrass fields (0.25 and 0.16). It is likely that the greater
moisture content of brome sod has enhanced the soil environment of
earthworms and other arthropods on which the short-tailed shrew
feeds.
All of the other local small mammal species were secured from
brome habitat type except for the southern bog lemming.
Although mature grasslands are not a habitat frequented by
the house mouse, it occasionally appears in these situations. This
41
may depend more on the nature of the surrounding habitat than on
characteristics of the grassland through which it is probably passing
to reach more favorable areas. Whitaker (1967) suggests that the
combination of its foraging behavior and its desire for cover restrict
it to mature cultivated locations. Since these locations usually
prevail for only a short period of time, the house mouse leads a
nomadic existence in search of suitable habitat. Given this, the
decline from 0.3 individuals per trapline in the forties to 0.08 in
the seventies probably reflects the reduction in cultivated and
annual grass and weed associations that these animals would be moving
between. Undoubtedly the same situation pertains for the woody
hedgerows and forest margins from which house mice were captured in
the forties, but not in the recent surveys (see Tables 4 and 5).
The seed-eating meadow jumping mouse was much less abundant
in the monotypic grass associations than in those having both grass
and weeds. It was captured at the rates of 0.77 and 3.94 per trap-
line, respectively. This difference may, in part, be due to reduced
seed abundance. However, for the other seed-eaters, the insignifi-
cant difference in captures of the white-footed mouse and house mouse,
and the small reduction in capture rate for prairie deermice suggests
that another habitat requirement of the jumping mouse may not have
been met. A higher stem density in the perennial grasslands was an
obvious situation that may make travel in these fields difficult for
the jumping mouse.
42
Probable reason for why the meadow jumping mouse was not
caught in the 19405 investigation was discussed in the section on
perennial grasses and weeds.
The white-footed mouse is a seed-eater of late Oldfield
succession and of woody habitats. Yet trapping in both perennial
grass and weed associations and perennial grasslands yielded a modest
catch of 0.4 mice per trapline. The distribution of captures with
respect to trapline placement revealed that these captures were con-
fined to traps in close proximity to bordering hedgerows. Grasslands
should, therefore, be considered marginal habitat for the white-
footed mouse, and the extent of their utilization of these habitats
be considered dependent on the management of directly adjacent
tracts.
Smooth brome grass fields in various stages of succession now
cover 43 percent of the 325-hectare study area. Such dominance
attests to the success this grass species has had in establishing in
the more fertile lands abandoned following farming operations. The
brome grass has not, however, spread into the bluegrass-weed fields
that developed on the infertile sandy soils before the introduction
of brome grass. There is apparently little threat of this grass
spreading into the native grasslands that developed as a seral stage
following the lumbering in southern Lower Michigan. However, its
dominance in abandoned farmland and on highway rights-of—way (where
it has spread following construction or been sodded in) seems to have
been of great consequence to the grassland small mammal community in
Lower Michigan.
43
Mixed Perennials and Shrub Association
Perennial forbs are replaced by a number of woody plants that
gradually become of increasingly greater importance in the vegeta-
tion. Shrubs seldom completely occupy an area to the exclusion of
all other types of plants. Usually they are present in aggregations,
with perennial grasses and forbs in the open spaces between and a
number of trees scattered over the area. However, group plantings
for wildlife management result in more discrete, monotypic stands or
rows of shrubs.
Forties
In his study of field borders in relation to farming prac-
tices, Linduska (1950) examined eight sod fencerows for comparison
with brush-tree borders. These sod borders were grown up principally
to stands of bluegrass (Poa pratensis and P. compressa) with a variety
of vines and shrubs providing a secondary vegetative structure
absent from the open grasslands. Numerous shrub plantings for wild-
life food cover and for erosion control placed scattered patches
directly into this advanced oldfield seral stage.
Small mammal populations in these transition type communities
had lower densities than did those in adjacent croplands during the
same period. These two habitat types showed parallel seasonal vari-
ation in the relative abundance of the resident species. During
early August of 1942, four of these sod borders yielded 11 individuals
including 6 prairie deermice, 2 meadow voles, 2 bag lemmings and l
short-tailed shrew. In late October and early November of that year
44
four sod borders, including two examined before and two new ones off
the area, were trapped again. Of 77 small mammals captured in this
period, 50 were meadow voles, 19 were short-tailed shrews, 3 were bog
lemmings, 3 were prairie deermice and 2 were house mice. Concurrent
October and November trapping in craplands resulted in a higher catch
of prairie deermice but a far lower catch of meadow voles. During
April 1946, a few border habitats were sampled once more. In this
trapping ten lines took a total of 58 individuals, which included 21
meadow voles, l7 bog lemmings, 8 short-tailed shrews, 6 house mice,
3 prairie deermice, and 3 masked shrews. Several of these lines also
appear to have been operated off the area in nearby farmland.
Considering only results from traplines Operated on the
central research area, these semi-open oldfields and border strips
supported the most diverse small mammal assemblage of all cover types
examined. The observed small mammal species also were present in
more nearly equal numbers than in other habitats (see Table 4).
In general, transition areas like grass-shrub fields support
a mix of vegetation types and structural profiles. By this very
fact one would expect that some individuals of species normally found
within areas supporting the various components of the mix might venture
into this border habitat, with some taking up permanent residence.
In addition, lands with border vegetation frequently act as dispersal
routes between major habitats. Both of the above circumstances would
promote greater species diversity than that found in the surrounding
major cover types, as was found in this study. However, more frequent
and long term trapping would have been necessary to determine the
45
real extent to which any such dispersing non-residents may have con-
tributed to the net catch here.
The predominance of grass cover over shrubs in these units
still favors the prairie deermouse. The capture rate for the prairie
deermouse was 1.43 individuals per trapline and for the white-footed
mouse was 0.31 per line. This di5parity existed whether in semi-open
oldfields, (1.41 and 0.08 mice, respectively) or in sod strips border-
ing croplands (1.75 and 0.43).
The mixed perennial and shrub association was the only upland
cover type from which the masked shrew was secured in the forties.
Only three individuals were captured in regular trapping. However,
six other of these shrews were trapped in November and December and
two additional ones in March during an eight-month study on the
homing ability of prairie deermice in oldfields over the winter of
1942-43. The short-tailed shrew was also more abundant in bluegrass
sod borders than in the more open grasslands or croplands. The over-
all distribution of the short-tailed shrew was found by both Linduska
(1950) and Dambach (1944) to parallel the location of thick ground
litter and loose soil. Populations were much higher in ungrazed
woodlands and in field border situation than they were in similar
unites where grazing occurred. In explanation of these population
differences Dambach stated that invertebrates in an ungrazed tract
were two and one-halftimesas plentiful as in a grazed area and
that freezing of the soil is much less severe in ungrazed woodlands.
With reference to this point, a comparison of short-tailed shrew
46
abundance in perennial grass and weed associations, in perennial
grasslands, and in intolerant tree, shrub and grass patch regions
upholds this conclusion.
Perennial grass and weed fields of the forties were young
hayfields where the soil had been tilled in the last three to four
years. Trapping here averaged 0.25 shrews per line compared to 4.8
in grasslands that had been fallow for up to ten years.
Perennial grasslands in the forties were grazed or recently
grazed pasturelands. Only 0.16 shrews were captured per trapline
compared to 1.10 obtained from grasslands retired from grazing for
nearly 15 years.
In the brushy roadside and fencerow borders supporting vege-
tation in the intolerant tree and shrub stage, the vegetation had
closed in to such a degree that little or no herbaceous undergrowth
was present. However, most of the border vegetation from this cate—
gory examined in the seventies supported a light growth of grasses
and herbs amidst a thick accumulation of litter. Trapping in these
two situations yielded 0.43 shrews per line in the forties compared
with 1.58 in the present investigation.
In contrast, although fields supporting mixed perennials and
shrubs were of somewhat different seral stages in the two time per-
iods, both were undisturbed areas with a substantial accumulation of
litter. Here the relative catch was more nearly equal, with 0.76
shrews per trapline in the forties and 0.87 in the seventies.
The differences in number per trapline may not seem that
great compared to differences seen for other species. However,
47
considering that captures of shrews are relatively rare events and
that individuals are rarely recaptured in subsequent efforts due
to high mortality when confined in a trap, the numbers are rather
convincing.
In Linduska's survey, the southern bog lemming was most often
captured in early-stage transition habitats. He obtained an average
of 0.89 lemmings per trapline. As was the case with other grassland
habitats, there were seasonal differences in residency. Lemmings
and voles avoided these areas in the hot summer months, preferring
the wetland habitats instead.
Bluegrass sod hedgerows and border strips were the first to
contain bog lemmings at the onset of the fall upland migration. From
there they appeared to move out into shrubby oldfields (0.25 per
line, 24 lines), stream borders (observed 18 on a winter day at noon),
and isolated grass and weed patches having shrubby borders (7.5 per
line, 0.4 lines). However, the hedgerows still maintained relatively
high, (0.78 per line, 16 lines) and widespread (12 out of 16 trap-
lines caught lemmings) populations.
Linduska's survey of transition habitat concentrated on areas
with young shrub and conifer plantings from two to four years old
that were recently planted for wildlife, and on borderlands with
young shrubs or vines. The recent survey was not to replicate the
earlier study, but to examine how the maturation of these same lands
has influenced small mammal species diversity and relative abundance.
Consequently, trapping efforts on lands supporting mixed perennials
48
and shrubs were kept to a minimum, both by design and by scarcity of
qualifying habitats (less than 1 percent).
Seventies
The hedgerows surveyed in the recent investigation were not
very comparable to those just discussed above. They contained rela-
tively fewer seed- and fruit-bearing species and the shrubs were more
mature (8 to 10 years old). Red cedar (Juniperus virginiana), white
cedar (Thuja occidentalis), apple (Pyrus Malus), staghorn sumac
(Rhustyphina) and numerous oak saplings (Quercus 5pp.) were among
the common woody plants and either brome grass or bluegrass was the
principle ground cover. Hence, the white-footed mouse was more
abundant than the prairie deermouse, with relative densities per
trapline of 2.25 and 0.6, respectively. When this trapping occurred
in the Spring of1980, the prairie deermouse was at a low in its
population fluctuation, as well.
The southern bog lemming population was also at a low in the
spring of 1980 (see Table 8). There was abundant sign in the form of
characteristic droppings and runways from the previous fall. However,
prebaiting for one week and trapping for another in two separate
locations where they occurred before failed to catch any lemmings.
Even so, it appears that these hedgerows do sustain lemmings in years
when their populations are high enough to fill most appropriate habi-
tats.
49
Intolerant Trees,,Shrubs, and Grass Patches
This stage is composed of trees that are relatively intoler-
ant, that is, they require considerable amounts of light, they are able
to tolerate only moderate root competition, and their seedlings are
unable to grow under their own shade.
Forties
Vegetative cover composed of tolerant trees, shrubs, and
grass patches occurred in two different forms, isolated shrub or
tree patches (wasteland or plantings) and hedgerows, and comprised
only 2.9 percent of all cover types.
Uncommon were dry upland areas with scatterings of small
intolerant trees (average dbh 5 cm) including American elm (Ulppp
americana), black cherry (Prunus serotina), and black locust
(Robinia Psuedoacacia). The ground cover consisted of a thick leaf
litter, sparse grasses, and several species of bramble (Rpppg 5pp.)
including dewberry, blackberry, and raspberry.
The only small mammal species associated with these pre—
dominantly woody cover types was the short-tailed shrew (0.87 per
line). The significance of thick leaf litter to the presence of
short-tailed shrews was discussed in the previous section on mixed
perennials and shrubs.
In a comparative study Linduska (1950) examined fencerows to
determine the potential of hedgerow vegetation to form reservoirs
of crapland pests that could invade cultivated tracts at opportune
times. The wide variety of species found in the common bluegrass sod
50
borders was discussed in the previous section. Less common, and
only occasionally continuous with the bluegrass-shrub fencerows, were
the brush roadside fencerow representing the other extreme. In some
of these, woody vegetation had closed in to such a degree that little
or no herbaceous undergrowth was present. The principle trees and
shrubs in these situations included white and black oak (Quercus alba
and Q. velutina), shagbark and pignut hickory (Carya ovata and C,
glabra), choke cherry (Prunus virginiana) and black cherry, red maple
(Acer rubrum), hawthorn (Crataegus), staghorn sumac (Sambucus
canadensis), wild grape (Vitis), and others.
Hedgerows with primarily woody vegetation attract relatively
few small mammals. In early August of 1942, trapping in four wooded
borders secured only five individuals; four were prairie deermice and
one a white-footed mouse (Linduska, 1950; not included in Table 4).
In April 1946, two traplines in wooded borders caught only one white-
footed mouse. An analysis of Linduska's raw data (see Table 4) shows
that the only two small mammal species associated with these woody
fencerows were the white-footed mouse (0.75 individuals per trapping,
4 lines) and the short-tailed shrew (0.23 per line). At this stage
of woody plant succession the white-footed mouse is now obviously the
predominant resident deermouse. The scarcity of leaf litter in these
hedgerows, in conjunction with a low shrew population may corroborate
earlier statements about what are acceptable burrowing conditions.
51
Seventies ‘
From what can be determined, these woody hedgerows have not .
changed much from photos taken of the area in 1940. Sumac and the
other woody plants have increased in diameter and height. The larger
trees have also grown and spread into areas previously occupied by
the sumac. Thickness of the leaf litter has increased to the extent
that most of the grasses have been smothered out. Oak and hickory
seedlings are sprouting through the leaf litter in places where sig-
nificant seed pools exist. In addition to these border strips, sev-
eral of the wildlife plantings may now be categorized with the
intolerant trees and shrubs.
Transition to a game area program called for extensive wild-
life plantings in the form of food patches and cover plants. Woody
plants were placed in hedgerows and plantations crisscrossing the
study area, connecting many of the previously separated habitat types
with a common transition zone providing a network of dispersal routes
for small mammals. The many species planted include red and scotch
pine (Pinus resinosa and P. sylvestris), black locust, silver buffalo
berry (Sheperdia argentea), autumn olive (Elaeagnus umbellata), honey-
suckles (Lonicera spp.), multiflora rose (Rosa multiflora), hawthorn,
apple, and others. Woody plants associated with these plantings, but
not restricted to them, were staghorn sumac, grey-stemmed dogwood
(Cornus racemosa), the blackberry and the raspberry. Maturation of
these plantings by the late seventies has placed a considerable por-
tion of the land into the intolerant tree and shrub stage with brome
grass sod frequently beneath in patches.
52
Since a variety of different aged plantings are included in
this category, their combined capture results reflect a much more
diverse small mammal assemblage than what occurred in the more mature
woody hedgerows that Linduska examined (see Tables 4 and 5). His
objective was to obtain a clear contrast between sod fencerows and
those with woody vegetation and little ground cover. However, my
objective was to find the southern bog lemming. Since some of the
most productive cover types for lemmings in the forties were fence-
rows with grass sod and shrubs, this recent survey concentrated on
these trasition-stage border strips from the available range in
maturity of the wildlife plantings.
Only 0.09 prairie deermice and no house mice were captured
in these moderately-woody hedgerows, which are probably too woody for
these species (see earlier sections of more thorough discussions of
habitat use by these species). On the other hand, most of the other
local small mammal species were moderately abundant relative to their
other more preferred habitats.
Mark and recapture analysis indicated that three of the
species had individuals that were predominantly residents in their
habitat. These were the white-footed mouse, short-tailed shrew, and
masked shrew, whereas individuals of the other three species, the
meadow vole, bog lemming, and meadow jumping mouse, were largely
transients passing along these borders.
53
Mid-Tolerant Woodlands
In this stage an assortment of mid-tolerant trees, princi-
pally oaks and hickories, predominate. It is generally believed
that a mixture of beech, basswood, and sugar maple is the most toler-
ant, and therefore climax, vegetative type in Clinton County under
present conditions. The beech-maple-basswood stage will thus slowly
replace the intermediately tolerant oak-hickory type, although the
rate of succession will be extremely slow.
Forties
0f the central 225-hectare study area, 22 hectares were in the
woodland condition in the 19405. The great diversity in soil, litter,
vegetation structure, and plant species diversity among the area
woodlots (see Table 16) allowed for a broad examination of how wood-
land type might affect small mammal abundance and species diversity.
Seven woodlots, 4 to 10 hectares in size, were present in
this unit. Six were of the typical upland oak-hickory type, the
principle species being black oak, jack-oak (Quercus ellipsoidalis),
white oak, pignut and shagbark hickory, with an average dbh of 15
to 25 cm. Most had little or no middle story. The sparse under-
stories contained seedlings of the principle tree species along with
black cherry, sassafras (Sassafras albidum), ground juniper (Juni-
peris communis depressa), various brambles (Rubus spp.) and occa-
sionally other woody plants.
One woodlot was a lowland type in which maple dominated.
The principle species here was red maple, mixed with white, red, and
54
black oaks, pignut hickory, large-toothed aspen (Populus grandi-
dentata) and American elm. This woodlot has a very dense understory
of red maple seedlings and a tangle of grape (Vitis 5pp.), dogwood
(Cornus spp.), hazel-nut (Corylus sp.), witch hazel (Hamamelis
virginiana) and service-berry (Amelanchier sp.). No sod areas were
present in this woodlot.
Their past history showed that all were cut over for large
timber sometime within the 50 years prior to 1940.
In the recently grazed upland woodlots the soil tended to
be compacted and bluegrass sod was a predominant ground cover. This
provided a contrast to the more typical woodland conditions present
in those lots which had nearly recovered from light grazing. Even
then, most of the woodlots were young enough in 1940 that breaks in
the canopy allowed substantial patches of sad to develop.
The diversity of small mammal species captured in the mid-
tolerant tree and shrub stage for woodlands probably reflects the
great abundance of ground-layer vegetation and sad patches. Not only
were the white-footed mouse and short-tailed shrew captured, but also
the southern bog lemming, house mouse, and the woodland vole (see
Table 4). Previous investigations have stressed how important soil
and ground cover properties appear to be for the short-tailed shrew
(Linduska, 1950) and the woodland vole (Hamilton, 1938; Jameson,
1949; Benton, 1955). The latter usually requires loose, sandy soils
and deep humus suitable for burrowing, as well as an abundance of
root plants (grasses, shrubs, etc.) and tubers (woodland herbs) for
food. Young, open woodlots of the uplands provided these conditions.
55
The more mature lowland woodlots supporting tolerant tree
species still had open canopies and lush understories, but there were
no sod patches and few woodland herbs. Consequently, even these
woodlots should be considered in the mid-tolerant stage with respect
to small mammal habitat.
The heavy accumulation of litter over the entirety of the
lowland woodlots still attracted short-tailed shrews, but there were
no bog lemmings or woodland voles captured in these woodlands during
Linduska's survey.
Seventies
Since the early l940s, additional cutting has occurred in
only one of the central-area woodlots and all have been protected
from grazing by domestic animals. with the cessation of these
activities the woodlots have matured following the pattern of suc-
cession typical of most upland deciduous woodlots.
The canOpy has closed in above with the aid of maturing
second-story trees. This closure has reduced the amount of available
light for understory herbs and shrubs, allowing only spring woodland
perennials and shade-tolerant shrubs and saplings to persist. Sod
patches no longer prevail in the ground story except at the margins
of the woodlands where light penetrates from the side. Woodlots with
these characteristics were placed in the mid-tolerant tree category
in the present investigation because the ground story still supports
more vegetation than one would expect in a tolerant woodland.
56
The small mammal communities for woodlands now in the mid-
tolerant seral stage are more diverse than those present in the forties
(see Table 5). Although more diverse, the substantial reduction in
the density of understory shrubs and saplings may have caused a two-
fold reduction in the population of white-footed mice, from 3.22 to
1.44 individuals per trapline. Considering the relative abundance
of white-footed mice in all the sampled habitats in the 19405 versus
the 19705, the above conclusion is preferred over the alternatives
of (l) an overall low in p0pulation levels on the area; or (2) it
having been an artifact of more limited sampling in this seral stage.
For example, ample increases occurred in cropland (0 to 0.1), grass
and weed associations (0 to 0.4), grasslands (0 to 0.4), grass and
shrub areas (0.3 to 2.3), and in intolerant tree and shrub stands
(0.8 to 1.8).
The amount of land supporting woodland vegetation has more
than doubled since the 19405 and now totals 81 hectares (200 acres).
The majority of this land is in the mid-tolerant tree and shrub
category.
Some of these areas result from the maturation of oldfields
and very young woodlands; the rest is from tree and shrub plantings.
Several younger stands are open enough to support brome grass sod.
The greater diversity of small mammal species associated with
this seral stage in the seventies can mostly be attributed to the
fact that, in addition to trapping Linduska's lines, some trapping
was conducted nearer the woodland borders in search for the woodland
vole and the bog lemming.
57
Included here are the pine plantations that have reached a
stage of maturity where the litter layer, sod patches, and sparse
shrub associates resemble that present in the mid-tolerant deciduous
woodlands. Small, relatively stable bog lemming colonies were found
in these upland pine plantations throughout the summer of 1979. Their
only small mammal associates within these groves were white-footed
mice and short-tailed shrews. In the shrub hedgerows bordering one
such grove, these three species were joined by meadow voles, jumping
mice, and masked shrews. In another, more Open, grove individuals of
all five species were captured in neighboring traps.
Wetlands
Linduska Operated a few traplines in wetland habitats in con-
junction with his farmland study. Since no vegetation descriptions
were made of these sites, photographs taken during the study period
were relied upon for some basic information.
Areas on or bordering wet lowlands were primarily covered
with sedges. Reed canary grass (Philaria arundinacea) occupied
stream banks and formed patches around shallow ponds and lakes.
The few photographs available to characterize the willow-
maple-dogwood association showed shrubs approximately 1 to 2 meters
tall with a ground cover of sedges and mixed herbaceous plants.
Shrubs were fairly thick within a few feet of the water's edge and
thinned out farther from the edge. The principle shrub species were
red osier and grey—stemmed dogwood (Cornus stolonifera and Q,
racemosa), black willow (Salix nigra) and a variety of shrubby willows.
58
Also present were posion ivy (Rhus radicans), poison-sumac (Rhus
Vernix), water-hemlock (Cicuta maculata), marsh ash (Fraxinus
pennsylvanica), and some small red maples. In the very wet areas,
most sedges and reeds grew on hummocks Of soil and organic matter
emergent from the surface of the water.
Linduska captured only three masked shrews and four meadow
voles on three lines operated each for one three-day period. In such
moist situations the masked shrew predominates over the short-tailed
shrew; the latter rarely ever is captured in wetlands.
Although the only bog lemmings Linduska ever actually captured
in the vicinity of wetlands were taken from an adjacent lowland wood-
let, he makes several references to their association with wetlands.
Linduska (1950) observed an upland migration from the bogs and marshes
by Synaptomys in the fall. These movements coincided with the invasion
Of meadow voles into upland sod areas that neither species of mouse
occupied during the summer months. He speculated that both microtines
were moving into the grasslands, which in summer were dry and inhos-
pitable, but by fall were moist and suitable refuge from the season-
ally colder and eventually frozen wetlands. He also observed several
lemmings in a grass-weed Opening beside a stream bank in winter.
By the 19705, lowland areas have acquired a new growth Of mid-
tolerant trees. Box elder (Acer Negundo), black willow and black
locust have grown to an average dbh of 5 cm. multiflora rose, honey-
suckle, willow and dogwoods have matured, with stems approximately
3 cm in diameter. Vegetation is very thick around water edges and
59
new sprouts, 10 to 15 cm tall, appear further out from the shore in
the sedge, canary grass, and brome patches.
Much more extensive trapping was conducted in wetlands for
the present survey. This was primarily to assess whether upland
populations Of the bog lemming were higher or lower than those that
occurred simultaneously in the wetlands, or whether there were sea-
sonal migrations between the two regions.
0n the solid boggy borders Of lakes an equal mix of short-
tailed shrews, meadow voles, and meadow jumping mice was Obtained.
At both Burke Lake and Moon Lake these species each averaged 3 indi-
viduals per trapline.
Tamarack stands yielded no captures Of small mammals on any
of three occasions.
0f greatest significance to this study was the total absence
of bog lemming captures in wetland habitats even though a variety of
trap types were used, including Museum Special snaps, pitfall-can
traps, and livetraps. Microtine sign was abundant in many of these
locations. It had qualities similar to that described for bog lem-
mings by numerous authors, namely a light green color and blunt-ended
fecal pellets. But these qualities may be just as dependent on the
nature of the vegetation eaten as on the microtine's intestinal tract.
Evidence supporting this possibility was Observed in the upland pine
plantations. Here, fecal pellets that could unquestionably be attribu-
ted to the bog lemming appeared very dark green and blunt when formed
from brome grass and yet were small and tapered, much like that of
60
deermice, when taken from a trap from which the animal had eaten
oats. Hence, it is conceivable that a blunt, light green pellet
could just as likely be formed by meadow voles feeding on light green
sedges as by bog lemmings. If this is the case, then much of this
sign may be attributed to meadow voles. This is indeed a ripe area
for further investigation.
SPECIES ACCOUNTS
Cryptotis parva
In the northeastern United States, the least shrew is found
predominantly in Open grasslands (Blossum, 1931; Burt, 1946; and
Barbour and Davis, 1974) and abandoned Oldfields (Getz, 1962; Gotts-
chang, 1965; and Choate and Fleharty, 1973). Although this species
has occasionally been found in forest- or marsh-edge situations in the
northeast (Hoffmeister and Mohr, 1957), it is more often reported from
grassy or weedy fields in close proximity to wetlands.
What these weedy fields may provide is a diversity of broad-
leaved herbaceous plant species necessary to support a varied enough
insect diet for the least shrew. In a survey by Whitaker and Mumford
(1972) the five commonest foods of Cryptotis parva were found to be
lepodopterous larvae (18 percent), earthworms (11 percent), spiders
(7 percent), orthopteran internal organs (7 percent), and aphids
(4 percent). They also derived significant portions Of their diet
from centipedes, crickets, and mast. Such a variety of prey items
might only be supported by a large variety Of leafy herbaceous plants.
Howell (1954) saw evidence of habitat selection highly correlated
with cover vegetation within Old-fields duringa.live-trapping study
where he captured Cryptotis in only three Of seven cover types exam-
ined. He caught four individuals in Open growths Of bush—clover
(Lespedeza), 17 in goldenrod (Solidago) and sassafras, and three in
61
62
honeysuckle (Lonicera). None were caught in dense bluegrass stands
(Poa pratensis) with sparse goldenrod, in Johnson grass (Sorgygi
halepense), left fallow or in dewberry or blackberry stands.
Oldfield habitat supposedly suitable for the shrew was avail-
able in great abundance on the Rose Lake Area as both annual and
perennial grass and weed associations in the forties. This cover
type constituted 34 percent Of all major habitat types present on
the area. Even though 15 percent of the land supported this same
cover type in the seventies, trapping efforts in excess of 2000
trap nights for each study period captured so few animals as to sug-
gest that this species was, and still is, very rare on the Research
Area.
Many of the oldfields on land more recently acquired by the
State were never planted to hay, and were retired from cultivation
before the introduction Of brome grass. They, therefore, support a
greater diversity of weed species, and they support the native blue-
grasses. It is more likely that the least shrew will be found in
these Oldfields, since there is a great diversity of braOd-leaved
herbaceous plants and enough stability Of the plant community to
support a varied insect diet for the least shrew. There would also
be a greater amount of debris in these Older fields that might provide
suitable nest sites for the shrew (Whitaker, 1974).
Whether these factors are sufficient to attract the least
shrew if it were presently on the area is unknown. The inferences
drawn here about potential habitat selection, foraging sites, and
trappability mostly derive from publications of minor observations
63
made while the investigators were engaged in research on other spe-
cies, and some come from incidental encounters with the shrew. This
wide range of Observations is summarized by Whitaker (1974), but
even this large body Of literature does not give us a very clear
picture Of the ecology Of this species. Consequently, to say that
the least shrew is probably absent from the central study area, but
potentially present on the out-lying Oldfields more typical of
southern Michigan, is a "best guess" based on an overall considera-
tion Of literature published on the shrew.
Linduska (1950) reports of snap-trapping only two individuals
on the study area during the six-year period. A third individual
was found on 2 October 1941, apparently left by a predator beneath
an oak tree at an Oldfield-bog margin. In addition, one was col-
lected during the examination of field-shocked corn in January, 1941
(Linduska, 1942a; and Aldrich, 1978).
Four additional specimens were obtained from activities on
the Area over the years since Linduska's work. One was reported
killed by'a fox in 1946 (Gordinier, 1946), one was trapped in 1957
and two in 1960 (Aldrich, 1978).
In my own trapping in all seasons and with various trap
types (pitfall, snap, live) not a single least shrew was taken.
There is independent verification of this scarcity Of least
shrews if one looks at the owl pellets collected on the Area during
both periods. In 681 items taken in all seasons from five species
of hawks and three species of owls, Linduska (1950) found no least
shrews. I also found no least shrews in the 90 pellets I identified
64
from three species Of owls (see Table 7). These items were all from
winter collections. Should the species be extinct from the Rose
Lake Area at the present time (it probably is not), there is abun-
dant habitat to support viable populations should a re-invasion or ‘
population increase occur.
Despite the fact that this species readily builds nests just
below ground in Open fields (Hamilton, 1944; and Davis and Joeris,
1945), it has been most frequently collected during incidental dis-
coveries from above-ground nests beneath logs, rocks, sheet metal,
and boards (see Table 8). Davis and Joeris (1945) state that this
shrew is difficult to catch from March to November, which happens
to coincide with its reproductive season in the northern parts of
its range (Hamilton, 1944). Consequently, it is the information
gleaned from incidental discoveries, along with several captive
studies (Hamilton, 1944; Conaway, 1958; and Pheiffer and Gass, 1963),
which comprises the bulk of our knowledge about the least shrew. The
examination Of debris occasionally used for nesting by the shrew
may be a useful way to locate and capture these animals (Barbour and
Davis, 1974). However, one should not consider these Objects to be
a necessary component Of the least shrew's habitat.
Careful examination of the literature published on this
species suggests that there is a strong seasonal aspect to their
activity. It is interesting to note that in 90 percent of the
reported instances where this animal has been taken by trapping,
the captures have been made during the winter months from November
65
TABLE 7.--Prey items identified from owl pellets collected on the
Rose Lake Wildlife Research Area from February 24 to
April 1, 1980
a s
c: .0 g
"a? E =
(U f6 0‘6
x 1: > W '0
LIJ 3 r— 3 'F"
I6 >1 0 U S-
m m o m o. -v- 0
4.! 3 0:- : Q- '-
cu m > s: to 8f '4- '
.— s. Q) m z 31
r— d) S- Q. m (n
a) C .D 3 O 3 U) «A
Q. Ol- U, U C m U
U 06 :3 m I'd m S—
M- c 44 >1 m '- 3 "-
O X °I- O E 3 'l" L .0
d.) S- S- O +1 > 3 U,
. s. to u s. u v— -r- C
O O I— ‘I- 0) '0 >1 0 0
Z V) a: 2 O. a: (I) V) U)
Screech Owl 6
(Otus 6510) 3
Long-eared Owl 12 2 4 5 1 -- -- -- --
(Asio otus)
Great Horned Owl 23 __ __ 7 3 3 1 1 9
(Bubo virginianus)
66
pomp .cOmxuaa m~o_ _.La< m mopcmuca mN ..=.me_>
mma. .»a_tauux mam. scaacaa a mop u_o mu c_o_cu_o maxop
pmop .ucax xgaaunmu mm wowzm c_u Love: a» v .uo N Lw>vc com: xcoa Ammucu moxo»
consoouo o ocaogmcovca ~—
momp .m_cooa a mv>mo cansounmm ow ucaogmgouca .o» m assumoa mmmsu mmxw»
Nmm— .mxoocnuaocm Aguagnum or pages uomsm Love: a» m .vo ~ gouge an «cannon moxw»
mwm. .Lou»=m ama. ».=a-o==a coozuc.to a guaon no u=.p ua_to oregano
emwp .xmpomoz onmp ..uuo a, mo. Love: N «cabana u_o aegc
nwo. .ampe_cm .uaom .a.: .30“ m a:..oc.u .z
omm. .comgauua .naa n - .>oz e “sopca> e »u_=_o_> we. mm=.u_,=m see» :62
«ea. .coup_saz «mo_ .soz N a» m .ua . one: cauootaa Goa .Lo> so:
mam. _.ca< m acaocazovca _ u_o_cu_o
â€mm, sue»: a. veaocaamuca m u.~_cu_o
«no. .eo»,.2a: Luneo>az on xuoc Luvs: m ego» zaz
«No, .coS__soz awe. Logsosoz p _ u_m_c eucnupu-c.a= xtO» :uz
mmo. .Loccou .mop »_=a --m mucaoa Lace: 4 axouaue _av.h xomcua so:
amm. .Lmotan_.om a emu—o: mma. ._La< c. coo; rayon a» o .ua . mtsumoa--u.o_cupo xxuaucux
neg. .mmoa a Luce.uca .om. coco: a» e .u. . m.o=,ppu
«ea. .coa..sa: NNa. um=a=< om F ass)» uoxoc_coxo awmzouu
eem_ .eou__eaz Dem. gut»: m~ N new»: atom «uptopa
“no. .Lmocpcam mma. .uao .m «Fen emaca Laue: _ o__a saute .ooaeao xco outcopa
Louum_umo>c_ mama cowuwmmu .oz uuu_nm: wuoum
mczuogmupp mg» soc» cmxmu ago mm_cucw
.o>com mwuoumxcu mo new: An cowuump—ou mo moans..-.m ubm<h
67
to March (see Table 9). Davis and Joeris (1945) noticed this as far
south as Texas: "We observed that shrews rarely entered our live
traps as long as the weather was mild and natural food was present
in great quantity in the area, but after the first cold spell or the
fall, which came in early November in 1941, seldom did we fail to
catch at least one shrew each time our traps were set." Jackson
(1961) also mentions that in Pontiac, Michigan, several least shrews
were captured in window wells in successive evenings "just as the
first cold weather set in that fall." There is an indication that
winter may also be when predatory birds and mammals have their best
luck catching this species (see Table 10). Nearly all the reports
Of the least shrew in owl pellets are from collections made at winter
roosts. Although the ease of collection at these roosts may bias
such reports in favor of the winter months, there are also reports
of abundant captures in winter by hawks (COpe, 1949) and red fox
(Jackson, 1961). Incidental captures of least shrews from beneath
nesting materials, although reported throughout the year (see Table
8), are also slightly more frequent from the winter season. How-
ever, these captures cannot be thought Of as voluntary above-ground
activity on the part Of the shrews. This evidence lends support to
the notion that winter may be the best time to look for these shrews.
Davis and Joeris (1945) suggest that their increased capture
Of least shrews in winter may be the result of concentration by
these animals into areas of lodged grass favored in winter. These
same animals would then undergo wide dispersal in spring and summer.
TABLE 9.--Dates of trap capture of Cryptotis parva.
68
Entries are taken from the literature
State Habitat NO. Trap Type Date Investigator
Florida mesic (Old dune) 16 Sherman live Jan. 1969 Kale, 1972
Costal hammock 180 Museum sp.; Feb. 1969
mouse snap
same (none caught 1966-68)
Illinois Sparse grass field 1 Dec. 1934 Mohr, 1935
Indiana Oldfields 108 "Trap" Winter 1971 Whitaker, 1972
Kansas Shrubby Oldfield 1 Snap 8 Apr. 1923 Linsdale, 1928
Needy Oldfield 1 same 28 Nov. 1923
Michigan Open grassy hill near marsh 1 16 Nov. 1929 Blossum, 1931
Michigan Country fannhouse many Window Well 10 Nov. 1937 Matt, 1938
Michigan Oldfield 19 Multiplecatch 2-6 Dec., 1957 Getz, 1962
Same 4 Live-trap 31 Dec. - (None caught September to
Jan. 1958 November 1957
Michigan E. S. George Reserve 1 Sept. 1960 Master, 1978
Missouri Pitfall Sept. 1956 Conaway, 1958
New Jersey Grassy edge of pine woods 1 Snap July 1951 Conaway, 1953
Tidal meadow l Snap July 1951
New York Open field 1 "Trap" 18 March Hamilton, 1934
Ohio 01d 39 Mouse snap gohgzéc; Gottschang, 1965
Tennessee Hayfield 24 Live traps 28 July -
25 August 1951 Howell, 1954
Texas Grass pasture 2 Live trap 20-24 Oct. 1941 Davis a Joeris, 1945
Same 3 Live trap 12 Dec. 1941
Virginia Salt marsh 4 Live trap Sept. 1940 Hamiton, 1944
Same 1 Live Trap July 1941
TABLE'le-Dates Of collection of pellets containing Cryptotis parva.
Period of accumulation is provided instead when available.
Entries are taken from the literature.
Indiana
Kansas
Michigan
Michigan
Michigan
New York
Ohio
Oklahoma
Texas
Wisconsin
Wisconsin
Rough-legged Hawk
Short-eared Owl
Barn Owl
Long-eared Owl
Long-eared Owl
Screech Owl
Barred Owl
Barred Owl
Great Horned Owl
Great Horned Owl 3
Barred Owl 7
Barn Owl 27
Barn Owl 17
Feral house cat 3
Long-eared Owl 171
Barn Owl 102
Great Horned Owl 1
1
Red Fox 1
12 Winter 1954
27 13 Jan. Cope, 1949
99 Linsdale, 1928
1 Oct. Wallace, 1950
1 Dec. (all seasons
sampled)
Master, 1978
2 Sept. 1932-
May, 1933 Wilson, 1936
\JmU‘I
1 6 April 1935
18 April, 1939
Jones, 1937
Price, 1942
30 March, 1939
14 May, 1939
28 May, 1939
10 Jan., 1943 McMurry, 1945
Old--undated Davis, 1938
Undated--befOre
11 May
31 Jan., 1932
21 Feb., 1932
15 Dec., 1942
Davis, 1940
Nelson, 1934
Jackson, 1961
70
This behavior may be a significant aspect of their history since many
authors report Of sudden large concentrations Of least shrews in areas
where there were none previously (Peterson, 1936; Getz, 1962; and
Kale, 1972).
Microtus pinetorum
The woodland vole is most Often associated with mature hard-
wood forests where there are loose, sandy soils and deep humus
suitable for burrowing (Hamilton, 1938; Jameson, 1949; Benton, 1955).
Other habitats with similar soil and ground cover properties occa-
sionally support populations of this vole. Fitch (1958) collected
several voles from runway systems that were situated along the line
of contact between woodland and pasture within a BOO-meter strip of
woodland edge in Kansas. Paul (1970) frequently found woodland voles
in similar border situations in North Carolina, but these usually
bordered woodlands that supported larger populations within the
forest. Of the 90 specimens recorded for Michigan, most were taken
in deciduous woodlands with a well-developed ground cover of thick
litter or woodland herbs (Dice, 1920; Burt, 1940; and Linduska,
1950).
Linduska (1950) conducted fall trapping in seven woodlots
(6 upland, l lowland) at various intensities during his survey of
small mammals. This set Of woodlands encompassed a great diverstiy
Of soil and litter types, vegetation structure, and plant species
diversity. In preliminary trapping in one of the ungrazed woodlots
(Woodlot l) he collected four woodland voles in only 240 trapnights
71
from 9 to 11 August 1940. These were simply caught in livetraps
set atOp the litter using raw peanuts as bait; they were released
after examination. Three of these were captured in adjacent traps
(two within the same trap) and the fourth was taken an unknown dis-
tance away. Where these voles were localized within the woodlot
could not be determined from his earlier records. A total of 240
trapnights in one other woodlot that fall yielded no woodland voles.
Additional trapping in all woodland types included 2,503 trap nights
in the fall Of 1942 and 1946 and 150 trapnights in the early summer
of 1946. More than half of these trapnights were logged for the same
woodlot that had contained woodland voles in 1940. This sampling
effort involved a 204-trap grid run for seven days in October of 1942.
Despite this extensive effort, no additional woodland voles were taken
by trapping in his investigation. Woodland voles were reported to
be "abundant" (7 individuals) in field-shocked corn adjacent to wood-
lot 1 where the August captures were made in the winter of 1940-1941
(Rose Lake Wildlife Experiment Station, 1941), although none were
taken from shocks in any subsequent years.
In the intervening years between Linduska's study and this
late 19705 survey, four additional woodland voles were captured on
the Area. One each year in 1953, 1955, 1956, and 1966 was obtained
from the same woodlot as before (Aldrich, 1978).
These observations attest to the fact that populations Of
the woodland vole may be local and highly variable showing marked
fluctuations over time (Benton, 1955).
72
In the present investigation, I logged a total of 4,800 trap-
nights in and bordering woodland situations from 1978 to 1980. Nearly
half of this effort was devoted to surveying Woodlot l and adjacent
habitats. In trapping directed at capturing the woodland vole, sev-
eral procedures were utilized including livetraps, snap traps placed
both above and below ground level, and pitfalls with drift fences.
These were Operated mostly in late summer and fall Of 1978 and 1979.
In spite Of these pointed efforts, no woodland voles were taken by any
method in any season on the Rose Lake Area. I cannot at this time
Offer conclusive evidence for or against the existence of this spe- I
cies on the Area. Some woodland habitat appears favorable for this
vole. Many of the woodlots are continuous with grasslands, providing
an ecotonal margin supporting grasses mixed with woodland perennials.
Both Fitch (1958) and Paul (1970) found populations that were local-
ized within similar situations. The lowland maple woodlot (W-No. 7)
shows great potential for this species. There are extensive small
mammal burrow systems covering most of the woodlot, no doubt due to
the thick ground vegetation and deep humus layer. Limited trapping
in 1978 revealed only the white-footed mouse (Peromyscus leucopus)
and the short-tailed shrew. Unfortunately, no trapping was conducted
in this woodlot in 1979 when populations of the meadow vole and the
southern bog lemming were at a high level. Hamilton (1934), Burt
(1940) and Linduska (1950) found woodland voles to be syncronous in
their population fluctuations with the other local microtines. This
would probably have been the best time to find woodland voles active
in the woodlots, were there any to be found. With more land slowly
73
reverting to the mature woodland condition in association with grass-
land border, the potential for the woodland vole to establish more
stable, viable populations will increase with time.
Review of the literature on the woodland vole gives several
indications thow future investigators might implement censusing
efforts with the best timing and effectiveness:
1. Voles tended to be confined along the line of contact
between woodland and pasture (Fitch, 1958) and along edges and
Openings within the forest proper (Paul, 1960), usually in association
with a deep humus layer, heavy litter, or a thick covering Of ground-
layer perennials (Paul, 1970; and Goertz, 1971).
2. Most Of the evidence suggested a loose colonial associa-
tion. Even though habitat may be extensive and fairly uniform, wood-
land voles appeared to be clustered in scattered local colonies
(Hamilton, 1938; Benton, 1955; Fitch, 1958; Miller and Getz, 1969;
and Paul, 1970).
3. Since marked animals have been observed to be restricted
to localized runway systems, one should concentrate on burrow systems
when trapping (Fitch, 1958). These should include active or abandoned
burrows of moles because these are Often taken over and incorporated
into a runway system of the voles (Eadie, 1936; Jameson, 1949; Fitch,
1958; and Miller, 1964).
4. In woodlands where the same burrows are used by various
species Of small mammals, the only sure way Of establishing the
presence of woodland voles is by trapping them. This can be accom-
plished using snaptraps or livetraps set to one side Of a runway, or
74
pitfalls set across a runway, but all should be set below ground level
within the burrow system to maximize trapping success.
5. Equal captures of voles during daytime and nightime
periods may be Obtained during cooler months of the year. During
warm periods, these voles may restrict their activities to the lower
portions of their burrow system (Benton, 1955; Miller and Getz, 1969;
Paul, 1970; and Gettle, 1975).
6. Study periods could be selected short-term to coincide
with high population levels Of the other local microtines, with which
the woodland voles are Often syncronous (Hamilton, 1934; Burt, 1940;
and Linduska, 1950).
Synaptomys cooperi
Throughout its range the southern bog lemming is most Often
caught in spagnum-sedge-heath bogs devoid of standing water and in
abandoned upland fields, but are not restricted to those habitats
(see summaries by Connor, 1959, and Master, 1978). It is frequently
described as "uncommon." Lemmings may be locally abundant one year
and absent the next.
Linduska (1950) captured a total Of 41 Synaptomys over a
period of six years at Rose Lake. These were taken in various habi-
tats including sod hedgerows, brushy Old fields, winter corn shocks,
and Open grassy woodlots.
Presently, the bog lemming is as uncommon on the Rose Lake
Area as it was in the 19405. In both live- and snap-trapping only
20 Synaptomys were captured a total Of 45 times over a two-year period.
75
These were taken exclusively from pine hedgerows or plantations still
Open enough to sustain a modest grassy understory (see Tables 11-15).
Under such conditions, the lower branches contact the ground and
create a thick litter layer around the base Of each tree; a condition
which favors the presence of Synaptomys. Within the pine areas the
bog lemming feeds almost exclusively on brome grass. The content
Of fecal pellets from latrines, and of from stomachs removed from
those lemmings that were captured by snap-trapping in these groves,
consisted of a uniform dark green mash with few insects and no
conifer needles. Yet, a total of 425 traplines Operated for 31,876
trapnights in perennial grasslands (where the dominant plant species
also was brome grass, see Table 6) yielded no captures of Synaptomys.
Also canopy closure in the maturing woodlots has eliminated what sod
cover once supported lemmings.
The introduction of brome grass to the Rose Lake Area may
have reduced the cover available at ground level, since brome grass
occurs at a lower stem density and appears to lodge less than the
native bluegrasses. In the pine groves and hedgerows lemming surface
runways had been constructed in areas where the lodged grasses com-
bined with a thick needle litter to form a dense mat from 2 to 4 cm
deep in Open areas, and up to 10 to 12 cm deep around the bases of
trees. Subterranean burrows had been constructed 3 cm below the
soil surface beneath areas where only a sparse litter had accumulated.
These subsurface burrows existed as singular routes traversing the
bare regions between grass patches.
76
Subsistence on brome grass does not appear to have influenced
the reproductive capacity Of Synaptomys. All females captured during
this study period were reproductively active, either pregnant or
lactating. Two juvenals (8 and 9 grams) were also captured (see
Tables 11-15).
Connor (1959) correctly stated that the "chief requirement Of
Synaptomys seems to be the presence of green, succulent, monocoty-
ledonous plants, primarily sedges and grasses, which are its primary
source of food." However, the presence Of proper vegetation for food
may only be a necessary criterium for habitat selection, and not a
sufficient one. This factor may explain why “large areas Of appar-
ently suitable habitat Often contain only a single, small local colony
of lemmings" (Barbour and Davis, 1974). Careful scrutiny of their
distribution within those habitats occupied at Rose Lake and of the
many reports in the literature on lemmings in both upland and wet-
land habitats, shows that, within areas having favorable types of
food, physical factors greatly influence distribution. In most
studies moisture was the physical factor that exerted noticeable
influence on lemming distribution. The apparently necessary high
moisture level was most Often mediated by the presence of overhead
cover in the form of a highly structured ground litter or flora
(Hill and Hibbard, 1943; Miller, 1955; Mumford and Handley, 1956;
Lindsay, 1960; and Gottschang, 1965). In Open grasslands lemmings
Often localize where depressions or ravines expose a shallow water
table (Linsdale, 1927; Stegeman, 1930; Walter and Sollberger, 1939;
and Barbour, 1951). Of several bog habitats examined in Michigan,
77
TABLE ll.--S na tom 5 coo eri captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, fOr the years
1979 to 1980--Planted Conifer Stand-A
Date Status--First Capture Captures Comments
Females
7-11-79 Lact.; 19.59 1-snaptrap 106-14-16-10
MSU 28905
7-11-79 Juvenal; 89 l-snaptrap 81-15-15-7
MSU 28607
7-12-79 Pregnant; 249 l-snaptrap 117-17-18-11
MSU 28608
7-20-79 Juvenal;_ 13.59 l-livetrap
8- 7-79 Subadult; 16-319 7-snaptrap Pregnant 10-17-79
8-23-79 Adult, nonreprod,; 20-239 4-snaptrap Pregnant 8-29-79
8-21-79 Adult, nonreprod.; 20-239 9-snaptrap Pregnant 8-28-79
10-17-79 Juvenal; 99 l-snaptrap
7-21-79 Adult, early pre9.; 229 1-snaptrap Medium nipples,
imperforate vagina
Males
7-20-79 Adult; 209 abdominal l-snaptrap Hypothermic--died
MSU 28606 later that night
7-31-79 Adult; l7-26.59 abdominal 7-snaptrap Scrotal later
8- 5-79 Adult; 259 scrotal l-snaptrap
11-31-79 Adult; ca, 259 l-snaptrap Dehydrated--trap
had been set by
someone while trap-
line was closed
down
Associates
Sorex cinereus; Blarina brevicauda; Peromyscus leucopus; Tamias
striatus; Tamiasciurus hudsonicus
NOTE:
sparse and patchy (40-500 stems/m
Planted Conifer Stand--4-5 meters in height, 15 x 350
meters planted, with hedgerows ragiating from it; Bromus beneath,
) vegetation; Pinus sylvestris
is the predominant tree; Trapped 6/28/77-10/17-79; 4/30/80-5/9/80.
TSN, RlW, Sec. 23, NW}, SE}, NE}; T5N, RlW, Sec. 23, NEI, SW3, SW5.
78
TABLE 12.--§ynaptomys cooperi captured on the Rose Lake Wildlife
Research Area,’Clinton County, Michigan, for the years
1979 to l980--Planted Conifer Stand-B
Date Status--First Capture Captures Comments
Female
10-18-79 Lactating; 259 l-livetrap In 4 days trapping
Associates
Peromyscus leucopus; Blarina brevicauda; Tamiasciurus hudsonicus;
Microtus pennsylvanicus; Tamias striatus
NOTE: Planted Conifer Stand--4-5 meters in height, 100 x 350
meters planted; mixed forbs and grasses beneath, patchy; bordered
by old-field; Jack Pine (Pinus banksiai), Scotch Pine (Pinus
sylvestris), and Red Pine; Trapped 10/17/79 - 11/8/79, 577780 -
5-9-80*; TSN, RlW, Sec. 14, SE}, NW}, SEI, S}.
(*Disturbance by raccoons prevented any small mammal captures here
in 1980.
79
TABLE l3.--S a tom 5 coo eri captured on the Rose Lake Wildlife
esearc rea, Clinton County, Michigan, for the years
1979 to l980--Planted Conifer Stand-C
Date Status--First Capture Captures
Female
4/29/80 Pregnant; 259 2-livetrap
Male
5/7/80 Subadult; 199 2-livetrap
Associates
Sorex cinereus; Blarina brevicauda; Peromyscus maniculatus bairdi;
Tamiasciurus hudsonicus
NOTE: Planted Conifer Stand--4-5 meters in height, 70 x 130
meters planted; Bromus beneath in only two 10 x 20 meter portions
on the perimeter, sparse (50-500 stems/m2); bordered by shrubby Old-
field and coniferous hedgerows; Red Pine is the planted tree;
Trapped 4/16/80-5/9/80; T5N, RlW, Sec. 23, NW}, NW}, NE;
80
TABLE 14.-1§ynaptomys cooperi captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, fOr the years
1979 to l980--Conifer Hedgerow A
Date Status-~First Capture Captures Comments
Female
9—14-78 Lactating; 23.59 l~snaptrap Emb. 1L)(1R
28438 MSU - RC = 3mm
Male
1- 5-79 Subadult; 209 l-livetrap
Associates
Peromyscus leucopus; Blarina brevicauda; Tamiasciurus hudsonicus;
Microtus pennsylvanicus;’Tamias striatus
NOTE: None have been captured in this hedgerow since, even
with intensive trapping occurring during all of 1979.
Conifer Hedgerow A- 3-4 meters in height, 5 x 100 meters planted;
Bromus beneath, thick (500-1000 stems/m2); bordered by olive (Olea)
and devoid Of ground vegetation in this area; Red Pine is the planted
tree; Trapped 8/1/78—10/15/79; T5N, RlW, Sec. 23, SW}, SE}, SW5, E4.
81
TABLE 15.--S na tom 5 coo eri captured on the Rose Lake Wildlife
Research Area, Clinton County, Michigan, for the
years 1979 to 1980--Conifer Hedgerow B
Date Status--First Capture Captures Comments
_ Female
7-4-79 Lactating; 23 g l-snaptrap 97-15-17-12
MSU 28439
Associates
Peromyscus leucopus; Blarina brevicauda; Tamiasciurus hudsonicus;
Microtus pennsylvanicus; Tamias striatus
NOTE: Conifer Hedgerow--3-4 meters in height, 5 x 100 meters
planted; Bromus beneath, thick (500-1000 stems/m2); bordered by
Olive (Olea) and devoid Of ground vegetation in this area; Red
Pine is the planted tree; Trapped 6/25-8/29/79; TSN, RlW, Sec. 23,
NW5, SE5, NW5, SE5.
82
Synaptomys were most commonly found in wet bogs characterized by
numerous hummocks (Wilkinson, 1980) or low-growing shrubs (Getz,
1961) and on absence of standing water. Further substantiation for
this information can be found in additional references too lengthy
to list here.
In his 19405 survey, Linduska (1950) Observed an upland migra-
tion from the bogs and marshes by Synaptomys in the fall. These
movements coincided with the invasion of Microtus pennsylvanicus
into upland sod areas that neither species of mouse occupied during
the summer months. He speculated that both microtines were moving
into grasslands which in summer were dry and inhospitable, but by
fall were moist and suitable refuge from the seasonally colder and
eventually frozen wetlands. These seasonal movements were also docu-
mented by Connor (1959) for Synaptomys within the New Jersey Pine
Barrens. It is possible that both species have a high evaporative
loss Of moisture so that water loss becomes too great in the drier
situations to maintain a proper water balance (Lindeborg, 1952). In
Linduska's study, Synaptomys appeared first in upland sod borders
and hedgerows between cultivated fields. Later in the winter from
December to February, concentrations of the lemming were located in
numerous situations. One colony located in an aspen stand undergrown
by perennial weeds and bluegrass. A second one appeared in a sparsely
vegetated area on Coloma sand which supported oak saplings whose
lower branches were in contact with the ground and covered with lodged
grasses. A third was found in a shrubby wildlife planting on a
83
grassy hillside. Several lemmings also moved into corn shocks assem-
bled in the fields each fall. In all cases, there was abundant
vegetative cover at ground level. This cover was there in addition
to what the local grasses provided.
During the present study, Synaptomys also underwent dispersal
movements with the approach of winter. However, one need not assume
that these animals originated from the wetlands, since the upland
pine plantations supported lemmings throughout the summer. One of
the three pine plantations in which Synaptomus was found was moni-
tored during the summer of 1979 (see Table 11). The 13 resident
lemmings captured there were localized in three places within the
woodland where Openings in the canopy made possible a moderate
growth of brome grass and retention of lower branches on the trees.
Beneath where the grass had lodged over these branches, Snyaptomys
built nests and established feeding places and latrines. The major-
ity Of movement by the lemmings was most probably confined to an
underground burrow system which ran within and between grass
patches.
Apparently only those animals which were dispersing at the
time of capture were taken by trapping in pine hedgerows (see Tables
14 and 15). These animals were collected during periods Of high
movement by all the local small mammals (September, January, and
May) which was in evidence by the high turnover in the meadow vole
populations in adjacent grasslands. NO additional lemmings were
captured in these two hedgerows despite continuous trapping during
84
summers Of 1978 and 1979 and frequently in other seasons. These
lemmings may undergo short excursions down a hedgerow system and back.
These movements were revealed by a mark-recapture study. Marked
animals from Hwepine grove were captured in traplines set along these
rows, while no lemmings were captured out in the adjacent grasslands.
These Observations further support the notion that a moderate amount
of vegetative structure overhead is important to this species.
Synaptomys in upland habitats behaves as a typical microtine,
having multi-annual population fluctuations. Although Linduska (1950)
Observed annual fall irruptions of this species into the uplands, a
longer cycle was apparent. Over the duration of his study, he
Observed an upward trend in lemming population density that paralled
that Of the meadow vole, both peaking at the same time. The crash
was not monitored, but it was apparent that it would occur. One
complete cycle of the microtine population changes occurred over the
3 year duration of the recent investigation (see Table 16). Here,
again, the meadow vole and the bog lemming were syncronized in
their cycle. Other investigations in Michigan (see Table 17) verify
that cycling is a frequent occurrence and major aspect of Synaptomys
populations in this state. Likewise, Synaptomys cycles in unison
with the local microtines in other parts of its range (Beaseley,
1978; and Gaines gt_al,, 1977). This suggests that any significant
competitive interactions between Synaptomys and Microtus are probably
worked out in the area of habitat segregation. If there was any
direct interference competition occurring, then any numerical effect
85
TABLE 16.--Population changes for resident microtines over three years
1978 1979 1980
Summer Summer Spring Summer
Microtus pennsylvanicus in perennial grasslands
Qzï¬gg$glgï¬gd°f 32 (15-45) 108 (72-140) 31 3
No. Of grids 4 (100) 3 (100) l (100) 1 (100)
(trap/grid)
Trapnights/grid 800 800 600 600
1978 1979 1980
.F511 Summer Spring Summer
Synaptomys cooperi in planted pine stands
Average no. Of _ _ -
animals/line 0'3 (0 l) 3.3 (0 15) 0.3 (0 2)
NO. of lines 3 (25) 7 (25) 7 (25)
(traps/line)
Trapnights/line 150 550 70
86
mewsam cw coxmu N Azopv ommï¬
macaw m
cm :mxmp mp Apcavcanmv mnmp
.uoo cw Pmewcm F Azon mump
Acmacnmm
=_ :mxm» «F Apcmuczamv camp
xcmzcnmm cw vow
«cum m cw m— Acossoov memp
coucwz
cw coesou.uom ucmpa: cw
cmsssm cw meow Acossouv :mxmp m Acossouv Namp
cwsesm cw mcoc
xcmzcmq cw meow Azopv cmxmu mco: Azopv FemF
umczpamu mcoc Azopv :mxmu «so: Azopv camp
:mxmp mco xpco Azopv mmmr
papa meow o.m c?
:mxmu m Apcmucznmv mmmp
meowmn scam
pcmucznm cmwm mews: cw>m
umcsuamu mcoz Azopv ummp
mumpwnm; campa:
ages at Aacaucznav 8mm,
ommp cw cmwzm omm— .mxmzucwg memp .gwmpm camp .aszm me>
xuczou copcwpu zucaou copmmcw>m4
mOFucaou cmmwzomz ozu cw wcmaoou wxsoummcaw c? mpm>mp cowumpzaoa.irmpm4m<h
87
on either species' populations caused by the other would probably be
swamped out by the "overriding" effect Of the cycles.
Other evidence for or against competition between the twO
local microtine species is weak. Getz (1961) observed a strong avoid-
ance by Microtus pennsylvanicus for a shrubby section of the marsh
that Synaptomys preferred. In contrast, the lemming would readily
enter the habitat preferred by Microtus. Alicia Linzey at Virginia
Polytech is presently investigating this interaction to determine the
nature of their cohabitation Of grassland habitats.
Just as with Master (1978), the data from owl pellets at Rose
Lake may suggest a real decline in Synaptomys populations since the
19405. Linduska (1950) found 44 bog lemmings in a collection of 681
prey items in the pellets of several hawks and owls, 284 were
Microtus. In the collection Of pellets from the Area in winter and
spring Of 1979, no Synaptomys were found among 98 prey items taken
from three species of owls, of which 41 were Microtus. Likewise, in a
collection Of pellets that C. 1. Black Obtained from a Great Horned
Owl roost in Meridian Township, Ingham County, only one bog lemming
was found in 43 prey items, of which 23 were Microtus pennsylvanicus.
SUMMARY
The Rose Lake Wildlife Experiment Station was established in
1938 to provide information for the management of small game on
farmlands. One of the main functions Of the Station has been to
determine the response of farm wildlife to the new conditions estab-
lished in converting from exploitive to conservative farming. This
systematic appraisal of small mammals on the Rose Lake Area, the first
since the mid-forties, was in line with the long-term apsects Of
research at the Station and the broad scope of their Objectives.
In the early 19405 a farming program was set up under the
guidance of the U.S. Soil Conservation Service and Michigan State
College (now Michigan State University). A 700-acre livestock farm
employing new land-use practices was put into Operation. Crop rota-
tion, contour farming, level ditching, flooding, fence row develop-
ment, and woodlot management were practiced to enhance productivity
of both crops and wildlife.
The economic importance of farm rodents and their signifi-
cance as key organisms in the wildlife complex justified their inclu-
sion in the program. Hence, a major ecological study was performed
over several years, from 1941 to 1946, to investigate the status of
small mammals on this representative unit of Michigan farmland. The
study sought to determine (1) the comparative population levels Of
88
89
assOciated species in the various cropland, field, and woodland
habitats; (2) the effects of various land-use and farming practices
on population densities; (3) the interrelationships within the group
of small mammals and with other wildlife species; and (4) the bio-
logical information which might contribute tO a better understanding
of farm wildlife in general.
Management activities on the Area provided a great diversity
Of habitats for small mammals. Of the 1,172 acres in ownership by
1940, crOpland and pasture constituted 64 percent of the total area;
wetlands comprised 24 percent; and woodlots made up 12 percent
(Table 3). In the BOO-acre portion of most intensive study about
71 percent of the land was in pasture and crops; 16 percent in wet-
lands; and 13 percent was in woodlots. These land use percentages
were typical of the private farms in the immediate area.
Farming Of the area was diversified, with fields supporting
two crops having different maturation times. Crop rotation occurred
on all but the few muck lands. Strip-cropping was also used on the
largest fields. Corn, oats, and wheat were the principle cash crops
grown, and alfalfa and red clover were grown for hay production. The
prairie deermouse inhabited cultivated areas early on when there was
little to no herbaceous ground cover. The introduced house mouse
later joined the deermouse when adequate ground cover in the form of
mature crop plants and weeds became available. In 1950 the European
smooth brome grass was added to the hayfields.
Pasturelands, grown up principally with bluegrass and various
weed species, were maintained for livestock. Meadow voles occupied
90
the pasturelands, accompanied by prairie deermice at one-half the
density found in croplands.
The transition from livestock farm to a game area program
was initiated in 1962. Grain farming was continued on a share crOp
basis. This program provided for 25 percent of the crop to be left
standing for wildlife. Today, corn is the only crop which continues
to be planted by sharecroppers and Area personnel. Even this limited
sharecropping is in jeopardy of ceasing for lack of interest by area
farmers.
All the grasslands retired from cultivation since the intro-
duction Of brome grass onto the Rose Lake Area eventually became
occupied by this grass species. Today, these fields are essentially
monotypic, and very stable in this state. Their lack Of plant divers-
ity discourages seed-eating birds and mammals from inhabiting these
fields, and consequently the introduction of propagules from other
plant species is slow. The transition of these fields to a woody
condition is further curtailed by the apparent resistence the growth
form Of this grass has to the germination of other species. This
general cover type occupies 43 percent of the study area, and its
success has significantly altered the patterns of seasonal distribu-
tion and abundance in the grassland small mammal assemblage of meadow
voles and short-tailed shrews.
In the forties, meadow voles occupied upland bluegrass-weed
fields only during the fall and winter when moisture levels were high.
91
Populations averaged 0.85 per line and showed fluctuations Of an
annual nature.
In contrast, brome fields in the seventies usually retained
sufficient moisture to support meadow voles year-round. Population
levels are much higher, averaging 6.8 voles per trapline and fluc-
tuating from 1.5 to 15.1 per line Of twenty-five traps over a two-
year period. The absence of weedy plant species from these fields
excluded the prairie deermouse from this seral stage that it had
inhabited in the forties. Although the least shrew was taken in small
numbers from this seral stage in the past, its presence on the central
study area at this time is questionable.
The transition to a game area program called for extensive
wildlife plantings in the form Of food patches and cover plants.
Woody plants Of all types were planted in hedgerows and plantations
crisscrossing the study area; connecting many of the previously
separated habitat types. The maturation Of these plantings by 1980
has placed a considerable portion Of the land into the intolerant
tree and shrub stage with brome grass sod beneath. The earliest
plantings and retired Oldfields have now advanced to the mid-tolerant
tree stage, with grass patches interspersed throughout the woodland.
This range of woody cover types with grass patches beneath is favored
by the southern bog lemming (now considered a threatened species in
Michigan). White-footed mice, and an occasional short-tailed shrew,
occupy these sites. However, there is a distinct absence Of meadow
voles from these shrub-grass-tree areas. Maturation of these tracts
92
since the 19405 has more than doubled the amount of land supporting
woody vegetation. It now totals 200 acres (81 hectares). Hedgerows
continue to be planted along roadways surrounding the prOperty.
The upland oak-hickory and lowland maple woodlots were all
cut over for large timber sometime within the 50 years prior to 1938,
creating substantial breaks in their canopies. Grazing also occurred
in many of the woodlots on the herbaceous ground cover and under-
story shrubs prior tO the Linduska study. Together, these activities
had allowed substantial patches of sod to develop on many of the
woodland floors. One woodlot supported a population of the woodland
vole, and an occasional bog lemming was captured in several of these
timber stands. Since the early 19405, additional cutting has occurred
in only one Of the central area woodlots and all have been protected
from pasturing. With cessation Of these activities, the woodlots have
been allowed to mature, following a pattern Of succession typical of
most upland woodlots. The canopy has closed in above, aided by
maturation of the second story trees. Hence, only spring woodland
perennials and shade tolerant shrubs and saplings persist in the
interior, and sod patches have been eliminated from all but the
margins.
The effect of canopy closure and concomitant thinning Of the
ground story vegetation has been the reduction of white-footed mouse
populations to half of what they were in mid-tolerant woodlands in
the forties, from 3.2 to 1.4 individuals per trapline. For this
same reason the woodlots are no longer appropriate for either the
93
southern bog lemming or the woodland vole. However, much of the 81
hectares now in woodland condition is in an early mid-tolerant tree
and shrub category that, at this point along with intolerant wooded
areas, seems favorable to both species.
Wetlands on the central study area, which in the forties were
surrounded by grasses, sedges, reeds, and a few woody associates in
an early seral stage, are now surrounded by thick zones of more mature
trees and shrubs. In addition to masked shrews and meadow voles,
which were caught in limited trapping in the forties, white-footed
and meadow jumping mice were captured within these habitats in the
seventies.
RECOMMENDATIONS
It is apparent from this study that major modifications in
both censusing methodology and habitat preservation be made for three
of our threatened or rare small mammal species, the least shrew
(Cryptotis parva), the southern bog lemming (Synaptomys cooperi),
and the woodland vole (Microtus pinetorum).
The suggested changes in our routine search for these species
are carefully outlined in the Methods and in the Species Accounts
sections Of this text.
It is highly recommended that several diverse mid-successional
upland habitats ranging from Oldfields supporting native grass and
weed associations to early mid-tolerant woodlands be maintained in
patchy interspersion. Such arrangements are similar to what commonly
occurred in Lower Michigan when natural disasters, such as fire and
flood, went unaverted.
All three small mammal species are widely reported to have
scattered, loosely colonial associations during most of the year,
even though habitat may be extensive and fairly uniform. This behav-
ior is considered by this investigator to be reflective Of their
association with rapidly changing transition habitats. For example,
the least shrew is Often found in a nesting situation with several
other individuals, and often inhabits grassy or weedy fields in close
94
95
proximity to wetlands (see summary by Whitaker, 1974). The woodland
vole is frequently found in colonies within ecotonal margins supporting
grasses mixed with woodland perennials (Dice, 1920; Linduska, 1950;
Fitch, 1958; and Paul, 1970). The most versatile in its association
with transition habitats is the southern bog lemming. This species
can be found in a wide range of both wetland and upland habitats
wherever there is monocotyledonous vegetation contiguous with
overhead cover in the form Of highly structured ground litter or
flora (Hill and Hibbard, 1943; Linduska, 1950; Miller, 1955; Mumford
and Handley, 1956; Lindsay, 1960; Getz, 1961, Gottschang, 1965; and
Wilkinson, 1980). Its reported scarcity probably stems from both its
colonial nature and from what are apparently frequent relocations by
these colonies. Hence, an interspersion of smaller patches in
various stages Of succession 'hs seen as more desirable than exten-
sive tracts of uniform cover type.
In the past, it was considered good management practice to
conceal fragile wetland habitats within thick zones of woody vegeta-
tion that might reduce human traffic. It is advisable that, at
least for the less fragile wetlands, a portion of wetland margins be
maintained in early seral stages having native grasses, sedges,
spagnums, or reeds, mixed lightly with woody vegetation for the least
shrew, and the winter needs Of the southern bog lemming.
APPENDIX
96
MICHIGAN STATE UNIVERSITY
THE HUSEUM EAST LANSING - IIICRIGAN ° 40624
To: Field biologists
Re: Local population status of Synaptomys cooperi
There is a lack Of published infonmation regarding the population status and
habitats Of several of the less conspicuous small mammal species. Although these
species occur in such low numbers as to be unlikely research subjects, valuable
information on their habitat selection, life history, and population dynamics
may be collected incidental to investigations of the more common species. In light
of this, we are conducting a survey of the current populational status of the
southern bog lemming (§ynaptomys cooperi) in various parts Of its range.
Past records from Michigan document marked fluctuations in the bog lenming
populations, and presently we are both finding these rodents on the increase in
our study areas, Clinton county in southern M chigan and Gogebic and Iron counties
in the Upper Peninsula. This questionnarie is being submitted to mammalogists
with the distributional range of this species to inquire specifically about
1) present numbers of the southern bog lemming in their areas, and 2) if increasing,
what habitats are being used, and 3) if meadow voles (or prairie voles as the case
may be) and other small mammals are being influenced by this density buildup. Also
it would be useful if the person could determine the timing of probable subsequent
population declines in their areas. Information derived from your mammalogy class'
field studies is welcomed.
We are mainly trying to establish:
1) whether the population buildup in Michigan is strictly a local phenomenon,
or whether it has some common basis for occurance over the entire range
of the species;
2) whether any interactions between S na t s and associated species, par-
ticularly with Microtus spp., are responsihle for the population changes
observed;
3) what the refuge habitats for S na t s are in periods of low numbers, and
which ones they expand into in peah periods
Attached is the questionnaire and return envelope. Feel free to contribute
any additional observations you think may be useful regarding other aspects
of this species' biology.
Jac elyn L. Shier
Graduat Research Assistant Graduate Research Assistant
Phchigan Technological University Michigan State University
97
98
QUESTIONNAIRE ON THE POPULATION STATUS OF Synaptomys cooperi
In the course Of your recent field studies, have you located any
southern bog lemmings?
Yes No If no, and you have recently performed a field
study Of small mammals, please briefly describe
the study area and Observational methods in the
appropriate sections. If yes, please complete
all sections.
HABITAT: Describe in detail.*
Well drained _______ Describe:
Poorly Drained
Successional stage:
Vegetation description:
Small mammal associates:
LOCAL STATUS: Indicate whether high, low, scarce or absent.
Synaptomys cooperi Microtus spp.
Summer 1978
Winter 1978-79
Summer 1979
Winter 1979-80
Did you Observe any interspecific interactions which would indicate
that the species are directly affecting each others' population levels
or local distributions?
OBSERVATION METHODS: Indicate trap type, duration, and season, etc.
(or whether specimens were brought in without data).
COMMENTS: Comments on any of the above questions or additional
information on other aspects of Synaptomys biology in your area
(attach additional sheet if necessary).
*If you have information regarding more than one local population of
S na tom 5, please photocopy the questionnaire and record the
information separately.
BIBLIOGRAPHY
99
BIBLIOGRAPHY
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