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This is to certify that the

thesis entitled

Roost-Site and Habitat Selection of the Long-
Legged Myotis in a Managed Landscape on the East
Slopes of the Cascade Range

presented by

Jeffrey A. Taylor

has been accepted towards fulfillment
of the requirements for

MS degree in _Zleg¥_

 

Richard W! Hill

Major professor

Date December , 1999

 

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TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 chlRC/DateDuepes-ms

ROOST-SITE AND HABITAT SELECTION OF THE LONG-LEGGED MYOTIS
(Myotis volans) IN A MANAGED LANDSCAPE ON THE EAST SLOPES OF THE

CASCADE RANGE

By

Jeffrey A. Taylor

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Zoology

1999

ABSTRACT

ROOST-SITE AND HABITAT SELECTION OF THE LONG-LEGGED MYOTIS IN A
MANAGED LANDSCAPE ON THE EAST SLOPES OF THE CASCADE RANGE

By

Jeffrey A. Taylor

Habitat fragmentation is often considered one of the biggest threats to bats in the Pacific
Northwest. Yet, few studies have focused on how bats use habitat in heavily fragmented
areas. The Northwest Forest Plan was created because of concerns about how the loss of
late-successional forests affected wildlife. This study focused on how Myotis volans uses
habitat in the managed forests on the east slopes of the Cascade Range, including whether
they will use retention such as live trees or snags left in harvest areas. During this study,
male long-legged myotis were radio-tracked to their day-roost locations, which were
primarily grand fir snags. Actual roosts were compared to random snags to see what
features are driving selection. The results of this study found that Myotis volans prefers
late-successional forests. They avoids harvest units, even when potential roost structures
are available, but will use retention that provides large structures such as aggregate
retention and shelterwoods. There is a high dichotomy in the types of roosts being used
between the two study sites that appears to be based primarily on whether it is high or low

canopy cover, which likely affects the microclimate of the roost.

ACKNOWLEDGEMENTS

Funding and logistical support for this project was provided by the USDA.
Forest Service and Champion Pacific Timberlands, Inc. Additional funding was provided
by Bat Conservation International and the Washington Department of Fish and Wildlife.
I am especially thankful to Jessica Eskow of Champion Pacific Timberlands, Inc. and
Rolando Mendez-Trenaman of the Gifford Pinchot National Forest for all of their time
and effort. Without their unwavering support this project would not have been possible.
In addition, I sincerely appreciate the hard work and dedication of my field assistants
Linda Lenz, Greta Turschak, and Sam Latra. I would like to thank my advisor Richard
W. Hill for all of his guidance, patience, and support. In addition, I am grateful to my
committee members Henry Campa and Donald 0. Straney as well as the Department of
Zoology and the Ecology, Evolution, and Behavioral Biology Program (EEBB) at
Michigan State University for their support. Finally, I would like to thank Patrick Allen
(CPU) for his help on the GIS work and the Washington Department of Natural

Resources for allowing me to use their lands for this study.

iii

TABLE OF CONTENTS

LIST OF FIGURES
LIST OF TABLES
INTRODUCTION
Study Area
METHODS
Available Habitat Areas
Stand Type Classification
RESULTS
DISCUSSION
MANAGEMENT IMPLICATIONS

LITERAURE CITED

iv

11

16

18

21

36

42

46

FIGURE 1:

FIGURE 2:

TABLE 1:

TABLE 2:

TABLE 3:

TABLE 4:

TABLE 5:

TABLE 6:

TABLE 7:

TABLE 8:

TABLE 9:

TABLE 10:

TABLE 11:

LIST OF FIGURES

Study Area Map

Drawings of Retention Types

LIST OF TABLES

Bat Species Captures in Study Area

West site Roost Attributes

East site Roost Attributes

Roost Height to Canopy Height Comparisons
Comparison of Roost Attributes: West to East
West site Snag Species Selection

East site Snag Species Selection

West site Snag Class Selection

East site Snag Class Selection

West site Habitat Selection

East site Habitat Selection

10

25

26

27

28

29

3O

31

32

33

34

35

INTRODUCTION

Ecosystem management of Pacific Northwest forests has experienced many
changes in recent years. An expansion of our understanding of forest ecosystem
processes, a shift in values among the American public, and new laws and regulations
regarding forestry practices have changed the ways that forest managers do business. The
controversy over the northern spotted owl (Strix occidentalis caurina) and other late-
successional species led ecologists, forest managers, and politicians to develop a
comprehensive management plan for the conservation of wildlife, fisheries, and
watersheds, while still meeting the mandate for continued timber harvests. In 1994, the
Forest Ecosystem Management Assessment Team (FEMAT) developed the Northwest
Forest Plan in an attempt to find an acceptable middle ground between these two
objectives (FEMAT 1993).

In the five years since FEMAT developed the Northwest Forest Plan, the US.
Forest Service has implemented a series of management prescriptions designed to provide
more connectivity to the landscape and to “soften” the effects of timber harvesting on
wildlife. These management prescriptions include leaving large structures in harvest
areas such as live trees, standing dead trees (snags), and down woody debris. Collectively
these structures are called retention. There are several major types of retention that are
used as management prescriptions including dispersed and aggregate retention,
shelterwoods, and riparian buffers (see Figure 2). Development and implementation of
these management prescriptions requires adaptive management decisions (McIver and

Bull 1998). That is because most people demand changes to occur within a political time

frame. But, this time frame is far too short to monitor and study ecological responses to
these prescriptions. Because these prescriptions are based on adaptive management
decisions, many of these prescriptions have been implemented without strong evidence to
show that they actually work in mitigating the effects of timber harvests on various
wildlife species (McIver and Bull 1998, R. Mendez pers. comm.) Therefore, there is a
need for research to determine whether these management prescriptions actually work for
the wildlife species for which they were intended, so that these mitigation measures can
be modified in the future to better suit the needs of wildlife.

One group of species for which management prescriptions have been intended is
bats. In recent years, bat conservation has become a major issue for forest managers
because of suspected population declines and the lack of basic knowledge about bat
ecology. Bats rely on the habitat in which they live for roosting and foraging, and a loss
of critical habitat features could result in the local extirpation of these organisms
(Humphrey 1975, Thomas and West 1989). Habitat fragmentation is often considered
one of the biggest threats to bat populations. However, few studies have studied bat
ecology in heavily fragmented areas (Campbell 1996, Fenton 1997). Many of the studies
on bats in the Pacific Northwest have focused on bat associations in old-growth forests
(Thomas 1988, Thomas and West 1991, Christy 1993). In recent years, the conservation
of bats has attracted the interest of timber companies and agricultural interests because of
bats’ high levels of insect consumption (Whitaker et a1. 1977, Kunz 1982, Reis 1982,
Whitaker 1993). In addition, many timber companies developing Habitat Conservation
Plans (HCPs) with the US. Fish and Wildlife Service are now being required to include

bats in their management plans (Hansen 1995). Landscape ecologists are also interested

in bats because they are considered well suited as indicators of general environmental
conditions because of their small size, mobility, and longevity (Fenton 1997).

Twelve species of bats occupy the forests of the Pacific Northwest. All are
insectivorous and are in the family Vespertilionidae, order Chiroptera. Historically, little
information has been available on bat ecology because they are nocturnal, volant
creatures, which makes the study of them somewhat difficult. Until recently, information
on habitat utilization for the small bat species of the genus Myotis has been primarily
anecdotal. Information regarding roost—site selection and habitat use for Myotis species
was nearly impossible to gather. Until the mid-1990’s, the smallest radio-transmitters
weighed greater than 0.8 grams. This was too large to attach to bats of this genus,
because all Myotis species in the Pacific Northwest generally weigh less than 8.0 grams
and these transmitters would weigh greater than 10% of a bat’s weight (van Zyll de J ong
1985, Aldridge and Brigham 1988). However, recent advances in technology have
reduced transmitter size to less than 0.5 grams, now allowing for telemetry to be
conducted on bats as small as 6.0 grams, while keeping extra weight to less than 10% of
body weight.

The long-legged myotis (Myotis volans) is one of the 12 species of bats that
occupy the forests of the Pacific Northwest. It is the largest Myotis species in the Pacific
Northwest (Nagorsen and Brigham 1993). This species occupies montane forests and
semi-arid rangelands across much of the western United States and western Canada
(Nagorsen and Brigham 1993). The US. Fish and Wildlife Service listed this species in
1994 as a category two species (USDI 1994). It was also identified by FEMAT as being

associated with old growth forests, a species of concern due to reduced old-growth

habitat, and in need of further study because little information is currently available on
this species (FEMAT 1993).

It is now well known that many bat species in the western United States use snags
in forests for day-roosting (Brigham 1991, Campbell et a1. 1993, Betts 1996, Vanhof and
Barclay 1996, Kalcounis and Brigham 1998, etc.). This is true of the long-legged myotis
(Rabe et a1. 1998, Ormsbee 1997, Frazier 1997). However, there is little information on
how bats, including Myotis volans, select habitat for roosting, especially as compared to
what is available in a landscape. Currently, only two studies have been published about
the ecology of the long-legged myotis in the Pacific Northwest, and both were conducted
primarily on females (Ormsbee 1997, Frazier 1997). Ormsbee (1997) studied exclusively
female long-legged myotis in Oregon on the west slopes of the Cascades and found that
they primarily roosted in Douglas firs (Psdeuotsuga menziezii) and partially alive, hollow
western red cedars (Thuja plicata). Frazier (1997) worked mostly on females on the east
slopes of the Cascades. He found that they roosted primarily in grand fir (Abies grandis)
and ponderosa pine (Pinus ponderosa) snags. In addition to these studies, Rabe et al.
(1998) studied exclusively female long-legged myotis in northern Arizona and found
them to use only ponderosa pine snags. Information on male roosting behavior is
apparently lacking in the literature. This is a relevant point because it is known that there
are differences in roost structure selection and habitat use between males and females in
many vespertilionid bat species due to differences in social behavior (Kunz 1982). The
three previous studies on this species also focused on describing roosting habitat without

adequately testing how his species chooses roost habitat as compared to availability.

One of the primary limitations in determining habitat use versus availability is
determining what is “available habitat”. If one could determine approximately how far
away from a central point a bat will fly during any given night, then that distance can be
used to determine the area available for selection. A home range estimate can also give
researchers an idea of what distance bats will travel. However, determining the home
range of a bat or even the distance a bat will travel in a night is nearly impossible using
radio-telemetry because bats have high flight speeds and change direction frequently.

Previous studies of the long-legged myotis have compared habitat use to
availability across an entire watershed (Frazier 1997, Ormsbee 1997). However, there is
no ecological reason for selecting that scale of analysis because these units are based not
on bat behavior but, rather, on hydrology. Watersheds can vary greatly in size, but in the
western United States these areas can be quite large, often exceeding 50,000 ha. An area
as large as a watershed is likely to be well beyond the normal home range of any
individual bat. In order to scale down the area being used for analysis, one would need to
find some way of identifying the area that is available to a bat on any given night.

One factor that may limit bat movement is their ecological tie to water. Several
studies have shown that bats are ecologically tied to water sources and that limited water
sources can limit the movements of individual bats (Tidemann and Flavel 1987, McNab
1982, Christy 1993, Marcot 1996, Ormsbee 1997). If a limited water source keeps
individual bats in the same area night after night, then the distance that the bats travel
from that water source to the furthest roost-site can be used to determine what the
available habitat is for selection. Since the study area I used has limited and widely

spaced water sources, it presents an opportunity to limit the distance a bat will travel

during the study. The goal of this study was to learn about the ecology of Myotis volans
in a managed landscape at three spatial scales. These spatial scales include:

0 Fine scale: The actual roost structures being used at the two study sites.

0 Habitat scale: Habitat use compared to availability within each site.

0 Landscape scale: Does roost structure selection and habitat use shift across a
landscape as habitat structure changes?

Male long-legged myotis were the ideal sex for this study because they are solitary
and non-territorial. Females of this species roost in maternity colonies of a dozen to over
two hundred, and therefore it would be expected that many of the females captured at a
particular site would return to the same roost (U.S.F.S. unpubl. data). This would not
allow much power in determining habitat use for this species. As males are solitary and
were expected to be spread out across the landscape, each male would be an independent
point for habitat analysis. This study used radio-telemetry of male long-legged myotis to
determine the day-roost locations of this species at two sites, located approximately
sixteen kilometers (10 mi.) apart. The primary null hypothesis for this study is: male
long-legged myotis do not have particular habitat and roost structure preferences in this
region. Thus, habitat use and roost-site selection are the same as randomly available. In

addition, habitat use and roost-site selection do not change across the landscape.

Study Area

The study area for this project was located on the east slopes of the Cascade
Range near the town of Trout Lake, Washington (Fig 1). Both study sites were located in
the upper White Salmon River watershed (a National Wild and Scenic River). The
geology and topography are dominated by a volcanic landscape associated with Mount
Adams, 3742 m (12,276 ft). The elevation of the study area ranges between 640 m and
1064 m. The climate of this study area is typical for forests of the east slopes of the
Cascades. This area experiences hot, dry summers with maximum daily temperatures
averaging 28.2° C, but often exceeding 38° C in the hottest part of the summer
(W orldclimate.Com 1996a). The average rainfall during July and August is less than 1.0
cm per month and humidity is low (W orldclimate.Com 1996b). Most of the water
sources in the area are intermittent because of this annual summer drought, with the
exception of two rivers that are fed by the glaciers of Mt. Adams. The long-legged
myotis hibemates during the cold, wet months of October to April.

Within this study area were two study sites located approximately 16 km apart.
They are oriented west to east and are hereafter called the west site and the east site. The
west site is located primarily on the lands of the Mount Adams Ranger District, Gifford
Pinchot National Forest (Fig. 1). The east site is located primarily on the lands of the
private timber company Champion Pacific Timberlands, Inc. (CPTI) (Fig 1). Both sites
also have some land managed by the Washington Department of Natural Resources.
Precipitation decreases rapidly as a function of the distance east of the Cascade crest due

to the rain shadow effect. Yearly precipitation in this study area decreases from

approximately 150 cm at the west site to 110 cm at the east site. This results in a shifting
vegetation structure across the study area. The primary species associated with the west
site are grand fir (Abies grandis) and Douglas fir (Pseudotsuga menzeisii), with western
hemlock (Tsuga heterophylla), western larch (Larix occidentalis), and ponderosa pine
(Pinus ponderosa) being secondary constituents. The east site is in a transition zone.
Douglas fir and grand fir remain dominant tree species, joined by ponderosa pine.
However, western hemlock and western larch disappear from the landscape and Oregon
white oak (Quercus garryana) becomes a secondary component of the forest. At the
eastern edge of the east site, the forest structure shifts into a primarily pine/oak dominated

forest, with fir species becoming a secondary component.

 

Figure 1
Study Area Map

 

 

 

 

 

 

 

I
East Site endow Butte Tower
Gifford Pinchot
National Forest
.New Cave H \
FR 2" 141 Wash. DNR O
0 ‘ Little Mud
Springs Pond
Chapman
Addsson Sno—park Springs Trough
Champion Pacific
Timberlands, Inc.
West Site Skamanh Co. Klicldtat
C0. \

 

 

Circles represent Available Habitat Areas described on page 16

 

Figure 2

Drawings of Retention Types

   

 

 

Dispersed Retention Aggregate Retention

 

 

 

Shelterwood Riparian Buffer

METHODS

Approval for the capture of these bats was granted by the University Committee
on Research Involving Human or Animal Subjects at Michigan State University prior to
any trapping, AUF # 03/97-048-00. In addition, the Washington Department of Fish and
Wildlife granted scientific collector permits for 1997 and 1998. At the west site, bats
were captured at a lava tube entrance known as New Cave. This is the only known
available water source for approximately 2.0 km. The opening is about 3.0 m tall and
12.0 m across. A 3.0- x 12.0-m mist—net was strung across the entrance. Bats were
captured as they entered the cave at dusk from the surrounding forests to drink and forage
and the net was usually left in place until 1-2 hrs after sunset, unless the target number of
bats was captured prior to that time.

At the east site, bats were captured at a 3.0-m diameter cattle trough and a 7.5-m
diameter spring pond. These two trap sites are located approximately 400 m apart and are
the only known water sources for approximately 2.6 km. A 3.0- x 7.0-m mist-net was
placed over the cattle trough, while three to five mist-nets were strung around the
perimeter of the pond.

All bats that were captured were identified and recorded to species and sex. If
they were female, reproductive status was also recorded. All species other than Myotis
volans were then released. All female Myotis volans were also released. Male long-
legged myotis were placed into canvas bags and taken to the Mount Adams Ranger

Station, where transmitters were placed on them. The transmitters used for this project

11

were Holohil Systems (Carp, Ontario, Canada) 0.47 g or 0.51 g LB2 and Titley
Electronics (Ballina, N SW, Australia) 0.50-g LTl transmitters.

At the Mt. Adams Ranger Station, the transmitters were activated by soldering the
leads together. The hair between the scapulae of each bat was trimmed close to skin
level. Trimming allowed the glue to be in contact with the skin and prevented the
transmitter from being lost if the fur of the bat was shed. Once the fur was trimmed,
Skin-Bond® surgical adhesive (Smith and Nephew United, Largo, Florida) was applied
to the area and the transmitter was placed on top. Some glue was also applied to the sides
of the transmitter. Some of the long hairs on the periphery of the trim were placed into
the glue to allow for a better hold. The bat was then placed back into the bag and
returned to the place of capture for release. Day-roost location was determined the
following morning. If there was no signal at the capture location the following morning,
then a search for the signal was undertaken over a radius of about 2.0 km from the
capture site. Once a signal was received, the bat was tracked to its day-roost. The range
of a transmitter was usually about 1.0 km or greater.

In order to assure the accuracy of our roost-site locations, all investigators were
tested prior to actually radio-tracking these bats. A second party placed transmitters in
the forest and then all investigators were asked to locate those transmitters. Only after the
transmitters were located by all that were radio-tracking during this study, was the
principle investigator confident enough to trust the data of those investigators. In
addition, three transmitters that were shed from the bats were located on the ground

during this study. Considering these transmitters are less than the size of a dime and were

12

laying in dense forest litter, to find them only increases my confidence that the roost-site
locations for this study are accurate.

Once roosts were located various roost-site attributes were measured. Roost-site
attributes included; roost-tree species, height, diameter at breast height (DBH), decay
class, and canopy cover. In addition, a 15-meter radius plot (0.071 ha) was set up around
each roost. Within this plot, average canOpy height, average stem DBH, tree species, and
the number of snags were recorded. Measurements for trees in the plot were only
recorded if they were considered to be “canopy trees.” Canopy trees were defined to be
those that were at least 50% as tall as overlying canopy. This prevented seedling/sapling
trees and stumps from being included in the analysis.

For every roost that was used, a random roost-site was also located to compare
roost structure use to availability. The location of the random roost-site was determined
using a random number table. From the actual roost-site a number was chosen at random
to indicate the distance in meters and a second number chosen to indicate direction in
degrees. Because over 95% of the actual roosts were snags, all random roosts were snags
to simplify random roost selection and location. In addition, random snags had to be a
minimum of 6.4 m tall and greater than 24.9 cm DBH to be used. These numbers were
based on the smallest roost used by a bat in this study. These minimum numbers were
used to assure that random snags were bat “useable” by preventing dead saplings or
stumps from being included in the analysis. This helps to assure that the comparison is a
conservative estimate of use to availability. The distance to a random snag had to be
greater than 30 m from the actual roost to prevent an overlap of the plots and less than

200 m to assure the random roost was contained within the same stand. If the edge of the

13

stand was less than 200 m in the selected direction, then the first snag located greater than
15 m from the edge was selected, to assure that the entire random plot was located within
the stand. Once a random snag was found, all of the same measurements were taken as
for an actual roost site.

For analysis of roost attributes, a series of paired t-tests with Bonferroni
adjustments were used to compare actual roosts to random roosts at each site, as well as
comparing the actual roost results from west site to east site. Statistical analysis was
conducted using SYSTAT 8.0 (SPSS Inc. 1998). Twenty-two of the 35 bats used
multiple roosts during this study. Roosts could not be weighted by the number of days
they were used because the transmitter battery has a limited life and therefore does not
allow for accurate knowledge of the mean number of days a roost would be potentially be
used. This is especially problematic for those roosts that are used near the end of a
battery’s life. Thus, multiple roosts used by a single bat in such cases could not be treated
as statistically independent. To avoid problems of nonindependence, the characteristics
of all the roosts used by an individual were averaged, and the mean values were used in
statistical analysis.

Analysis of use versus availability for snag species, snag class, and habitat
selection was conducted using a computer program called “Resource Selection for
Windows” created by Fred Leban, University of Idaho. This program used the statistical
tests described by Johnson (1980) as the primary procedure for analysis.

The problem of non-independence also arose for use versus availability analysis.
Therefore, the proportion of habitat used by an individual bat over the life of the

transmitter was used. For example, a particular bat used two roosts during the time it was

14

being tracked. One roost was in a shelterwood and the other was in a pine/oak stand. For
that bat these stand types were weighted 0.5 and 0.5. If a bat used two roosts and both
were in a pine/oak stand, then that stand type was weighted 1.0. Weighting by bat
eliminates the problem of non-independence.

Snag class selection was analyzed using the same. Snag class categories were
based on the criteria of Cline et a]. (1980). There were five snag classes. Class 1 is the
youngest decay class. Snags in this class tend to show very little decay, are generally
intact, and most of the bark is still attached. Class 5 is the oldest decay class. Snags in
this class have extensive decay, are broken down to a fraction of the original height, often

riddled with woodpecker holes and other cavities, and have little, if any, bark remaining.

15

Available Habitat Areas

The Available Habitat Area (AHA) is defined to be the amount of area that was
potentially available for any individual bat to use in an evening. Each study site had one
AHA (see Fig 1). The AHA was created by drawing a radius from the water source to the
furthest roost used by a bat captured at that water source. The west site AHA had a radius
of 1.8 km. The east site AHA was two overlapping circles of radii 1.16 km and 1.56 km.
The two overlapping circles resulted because the east site had two water sources.

A large majority of the bats stayed within 1 km of the water source. It is believed
that bats stayed close because water sources are quite limited due to the annual summer
drought. In addition, the water sources were also areas of locally high insect abundance.
Nighttime telemetry indicated that many hats visited the same water source night after
night to drink and forage. The theory behind the Available Habitat Area is that once a bat
visits the water source at dusk, it can then leave in any direction afterwards to forage and
find the next day’s roost. Thus, a circle with a radius drawn from the water source to the
farthest roost-site is in essence an estimate of the habitat available for selection by the bat.
once it leaves the water source. An Available Habitat Area is not a home range, because
the actual area a bat travels through in an evening is not known. Instead an AHA
estimates what is available area for a bat to select for roosting once it leaves the water
source. This method is less arbitrary and results in a much smaller area of analysis than
the “entire watershed” approach used by Ormsbee (1997) and Frazier (1997), because it is
based on actual biological data. Within each circle, habitat polygons were mapped based

on USPS. and C.P.T.I. aerial photos. Habitat polygons are sections of forest containing

16

the same habitat structure. The aerial photos with habitat polygons were digitized for
analysis in a G.I.S. Field reconnaissance confirmed the location and vegetation class of
the polygons. This method was based on the work by Ganey and Balda (1994) and

Blakesley et al. (1992).

17

Stand Type Classification

All habitat polygons were placed into one of eight vegetation stand types. These
stand classifications were based on the work of Oliver and Larson (1990) and McGrath
(1997). However, they were modified to meet the characteristics of the vegetation and
management techniques of this study area. They are based on current available stand
structure. Species composition is affected not only by natural successional processes, but
also by timber practices and approximately 100 years of fire suppression.

Douglas fir (Pseudotsuga menzeisii) and grand fir (Abies grandis) are the
dominant canopy trees in all but the pine/oak stand type. However, the secondary species
composition of these stands gradually shifts across the precipitation gradient. At the west
site, the secondary species consist of western hemlock (Thuja plicata), western larch
(Larix occidentalis) and small amounts of ponderosa pine (Pinus‘ponderosa). At the east
site, ponderosa pine joins grand fir and Douglas fir as one of the dominant species.
Oregon white oak (Quercus garryana) becomes a secondary tree species, while western
hemlock and western larch disappear from the landscape. At the eastern edge of the east
site, the forests are dominated by ponderosa pine and Oregon white oak with firs
becoming only a secondary component. In the results and discussion section, the term
harvest units will be used. For this study harvest units were defined as the two earliest
successional stages (SI and SE), as well as shelterwoods and aggregate retention.Below

are the eight stand types.

18

Stand initiation (SI): Early-successional stage, mostly planted with Douglas fir, grand
fir or ponderosa pine, and often containing several other species for “stand diversity”. SI
is exclusively caused by clear-cutting within this study area, but can potentially be caused
by any stand replacement event such as fire. Stands are generally younger than 30 years

of age. The average tree DBH is less than 13 cm. The canOpy is less than 5.0 m high.

Shelterwood (SH): This is a management technique similar to the stand initiation stage,
except that large overstory trees are left in moderate density, evenly distributed across the
harvest unit. Shelterwoods tend to be dominated by Douglas firs, with a pine/fir
understory. Many of the overstory trees are wind-damaged because of their exposure.

This results in high tree mortality, as well as, many live trees with broken tops.

Aggregate Retention (AR): This is a patch of live trees of the pre-harvest stand density
that was left in a harvest unit. These aggregates are too small to function as interior
forest, especially in terms of stand microclimate. The aggregates are generally less than

0.5 hectares in area.

Stem-exclusion (SE): An early successional stage directly following stand initiation. In
this stage, high stem density results in total canopy closure and prevents any further stems
from growing in the understory. Stands are generally 30-50 years of age. Average tree .

DBH is 13-38 cm. The canopy height is 5-15 m.

Stem re-initiation small (SRS): A middle-successional stage. When natural or
commercial thinning begins to eliminate some of the overstory trees, the canopy opens up
or gaps are created, allowing new understory stems to begin growing. All understory
trees are still seedlings. These stands are generally 50—80 years of age. The average

dominant tree DBH is less than 38 cm. The canopy height is 15-30 m.

Stem re-initiation medium (SRM): A similar stage to stem re-initiation small, but more
advanced. Gaps are present and most understory trees are seedlings to pole-sized. These
stands are generally 70-100 years of age. The average dominant tree DBH is 38-53 cm

DBH. The canopy height is 25-35 m.

Stem re-initiation large (SRL): A mature late-successional forest stand. Usually large
gaps are present in the canopy and understory trees of all ages are present. These stands
are generally greater than 100 years of age. The average dominant tree DBH is greater

than 55 cm. The canopy height exceeds 35 111.

Middle to late successional pine/oak (PO): At the eastern edge of this study area the
forest shifts from one dominated by Douglas fir/grand fir to one dominated by ponderosa
pine and Oregon white oak. This pine/oak habitat does contain some fir component, but
the structure of the stand is much different than the fir dominated stands. The canopy
tends to be more open (between 30-70%) and understory trees of varying ages are present.

As pines grow taller than the oaks, there is high canopy height diversity.

20

RESULTS

A total of 234 bats of 12 species were captured during this study (Table l). Sixty-
three of these bats were Myotis volans, 60 males and three females. Of the long-legged
myotis captured, bats caught in the preliminary trapping phase and all females were
released. All three females were captured at the west site. Transmitters were placed on a
total of 50 male long-legged myotis. Roost-sites were located for 35 individuals, whereas
roost sites were never located for 15 individuals. In August and September 1998, a faulty
radio-receiver resulted in a reception range of only 100—400 meters, as opposed to the
normal 1-2 km. It is probable that this faulty receiver is responsible for many of the 15
lost transmitters. Some transmitters may have been lost when transmitters fell off the
bats into dense forests or bats left the study area.

Of the 35 bats located at least once, 18 were located at the west site and 17 at the
east site. This resulted in location of 31 west site roosts and 33 east site roosts. The

number of days a particular roost was used varied from 1-12 days.

Roost-site Attributes:

At the west site, long-legged myotis selected very tall, dominate snags, generally
over 32 min height and 68 cm DBH. Roost height and DBH were both significantly
greater for actual roosts than random roosts (Table 2). The number of adjacent snags and
overall stand DBH were not significantly greater for actual roosts than random roosts, but

the means were greater for actual roosts than random roosts.

21

At the east site, it appears as though there is a very different pattern of selection.
None of the roost-site attributes were significantly different between actual and random
roosts except the number of snags per plot. In fact, the mean roost height, roost DBH,
canopy height, stand DBH, and the number of trees per plot appear to be quite similar
between actual roosts and random roosts (Table 3). Only the number of snags per plot is
different, with the actual roost plots having significantly more snags than random roost
plots. The west site measurements are significantly greater than the east site for every
attribute, except the number of snags per plot (Table 4).

At both the west site and east site, random snags were significantly shorter than
the canopy height of the stand (Table 5). This is to be expected, as dead trees are more
likely to have their tops blown off by wind or destroyed through decay. At the east site,
actual roost snags were also significantly below the canopy. However, at the west site,

actual roost snags were at or above the canopy (Table 5).

Snag Species Selection:

Of the 64 roosts that were located, 61 were found in snags and three in live trees.
The live tree roosts were two Douglas firs and one Oregon white oak. The characteristic
that all three live tree roosts had in common with roost snags was cavities in the bark due
to woodpeckers and natural decay.

At the west site, grand fir snags occur at approximately the same frequency as
Douglas fir snags (Table 6). However, roost-site selection strongly favored grand fir

snags. Over 77% of the snags that were used were grand firs, while only 6% were

22

Douglas firs. A few other snag species were used in small numbers, but in every case
they resembled the grand firs in state of decay and bark exfoliation.

At the east site, grand fir snags are less abundant in relative terms than at the west
site. Yet, bats were using grand firs significantly more than availability (Table 7).
Douglas firs were used at about the same frequency as expected based on random
selection. Ponderosa pine snags are the most prevalent species in the landscape.
However, ponderosa pines were used significantly less than randomly selected snags

(Table 7).

Snag Class Selection:

At the west site, Class 1 snags were selected significantly greater than expected
(Table 8). By definition, these snags tend to be the largest, most intact snags available.
As they are the youngest, they provide more stability and a longer standing life than those
of more decayed classes. Class 2, the second youngest and intact class, showed no
significant difference, and therefore was used as frequently as expected. Classes 3 and 4
were selected significantly less than expected (Table 8). These snags are in states of
significant decay, and most have broken tops and little available exfoliating bark. While
none of the actual roosts or random roosts in this study site were Class 5 snags, snags of
this class are present in the landscape in relatively small numbers.

At the east site, it appears as though decay class selection is the opposite of the
west site (Table 9). The youngest decay classes were used significantly less than

expected, while the more decayed classes were selected more than expected. However, it

23

should be noted that the two youngest decay classes were used 45% of the time at the east

site. Thus, the avoidance of young snags at the east site does not seem severe.

Habitat Use Versus Availability:

At the west site, only one stand type was used significantly more than availability,
that was the stern reinitiation large (SRL) or the late-successional forest stands (Table
10). Over 83% of the roosts were located in this stand type. While stem reinitiation
medium (SRM) and stem reinitiation small (SRS) were used significantly less than
availability, they were the only other forest types used at the west site. These are the
other most mature stand types. These results seem to indicate that bats at the west site
were selecting the most mature forest types available and were avoiding harvest units,
even when retention was provided.

At the east site, SRM was used significantly more than availability (Table 11). As
there was no SRL available at the east site, SRM was the most mature stand type
available. Selecting the most mature stands is similar to the habitat selection at the west
site. However, what is quite different about the east site from the west site is that bats
were also found using snags left in harvest units.

While it appeared as though bats at the west site were avoiding retention snags in
harvest units entirely, there were bats at the east site that used snags in harvest units. At
the east site, 28% of the snags that were used were located in the harvest units. However,
of these, only aggregate retention patches were used more often than expected. These
aggregate retention patches resemble the older stand types in structure. At the east site

pine/oak was also used significantly more than availability.

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35

DISCUSSION

The long-legged myotis appears to show some very distinct patterns of roost-site
selection and habitat use across the landscape. However, selection of roost-site
characteristics does shift significantly across a landscape. This species appears to select
the most mature forest stands available. At the east site, the oldest forest stands available
were only of moderate maturity (SRM). Myotis volans selected these oldest stands. They
also selected moderately mature stands of pine/oak, and aggregate retention patches that
resembled the older stand types in structure, but not area (Table 11). However, when
both the SRM and late-successional stands (SRL) were available at the west site, these
bats selected the late-successional stands (Table 10). As this species selected the late-
successional stands almost exclusively at the west site, it appears as though this species
has a strong preference for these late-seral stages. However, when late-seral stages are
not available to them, as at the east site, these bats shifted to the next oldest seral stage,
SRM.

Some might note that at the east site this species did not use SRM exclusively. In
fact, bats were occasionally found using retention snags within harvest units. This may
lead to the conclusion that this species will roost in harvest units provided there is some
retention. It should be noted, however, that the three earliest successional stages (SI, SE,
SRS) were used less than availability (Table 11). Only in the cases in which large
structures were left in relatively high densities, such as the shelterwoods and aggregate
retention patches, did bats not avoid harvest units. Shelterwoods were only used about as

much as expected from a random model and aggregate retention patches were used

36

greater than availability (Table 11). Since these retention patches resemble more mature
stand types in structure, but not in area, this finding might have been expected, especially
where late-seral stage stands are lacking. The finding that bats never used retention
structures within harvest units at the west site supports this conclusion.

The fact that bats did not use SRM exclusively at the east site may only indicate
that SRM is marginal habitat for these bats. A stand structure of the maturity of SRM
may not produce the ideal microclimate that these bats are looking for. This may force
certain individuals to look elsewhere, sometimes seeking shelter in snags located within
harvest units. The results of this study suggest that late-successional forests including
possibly old-growth are the highly preferred habitat for this species. This conclusion is
supported by Harris et a1. (1982), Thomas (1988), and Thomas and West (1991).
However, when those late-seral stages are not available, this species appears flexible
enough to use younger successional stages, provided the necessary roosting structures
(snags) are available. This is consistent with the results of Ormsbee (1997).

While individuals may be flexible enough to use roosting structures in less than
ideal habitats, the implications are unclear for the population dynamics of this species.
The relative population densities of the two study sites were not measured in this study.
In fact, no studies of population densities have ever been done for this species. It is
unclear whether the reproductive success of this species is affected by habitat quality. For
this species to exhibit true habitat flexibility, it is not enough for individuals to use
marginal habitats, in addition, a population must be able to be reproductively stable in
that marginal habitat. It is possible that the east site could be a population sink. This site

could be occupied by dispersing males that have little or no reproductive success in a

37

marginal habitat. On the other hand, males may migrate in the late summer to breeding
areas located in higher quality habitat further west where the females are. As no females
were captured at the east site during this study, these scenarios are plausible. However, it
is unknown whether migration actually occurs among males. Assessment of reproductive
success and population dynamics is nearly impossible for bats species in North America.
Mark/recapture studies often fail because rarely can anyone recapture marked bats. It is
not even clear how long this species lives in the wild (van Zyll de Jong 1985). The only
means of assessment of population size is generally head counts of hibernating bats
(USFS unpubl. data). However, bats in a hibemaculum can arrive from many different
places. Thus, this method does not allow for an assessment of a particular
metapopulation. In addition, census by the method described can sometimes result in
high mortality for the bats because of disturbance during such an energetically sensitive
period of their lives.

Looking at finer scale roost-site selection, it appears that selection shifted from
west to east. At the west site, there was very strong selection for the largest snags
available. The structures bats selected at the west site were characterized as being Class 1
snags greater than 32 m tall. The snags were often at or above the top of the canopy
(Table 5). Ormsbee (1997) found that female long-legged myotis also used snags that
extended above the canopy. However, at the east site bats did not select snags that were
any different from random and in fact they selected snags that were significantly below
the top of the canopy (Table 5). East site bats selected all decay classes and showed some

preference for the most decayed of those classes.

38

One possible explanation for this shift in snag size and decay class selection may
be that snags located at the top of the canopy in closed canopy stands may produce a
microclimate similar to smaller, more decayed snags in open canopy forest stands.
Microclimate is an important factor for bats because of their unique physiology. Many
bat species in North America go through torpor during the day. This is a time when they
reduce their body temperature from 37° C to that of the ambient environment. This
reduction in body temperature reduces their metabolism and allows them to conserve
energy. However, when they emerge from torpor in the early evening, they must warm
themselves back to their active temperature using their fat reserves. However, if a bat is
roosting in a location that receives solar radiation in the late afternoon, this sunlight could
heat their bodies and thus would reduce the need to burn fat. Therefore, it may be
advantageous for bats to select roosts that will receive sunlight in the late afternoon, such
as the west side of a snag that extends above the canopy in a closed-canopy stand or
possibly a shorter snag in a more open canopy forest.

It would be very interesting to investigate the differences in microclimate in
various potential roosts. A valuable study would be to compare the microclimate of
potential roosts (i.e. under the exfoliating bark) in snags that extend above the canopy in
closed-canopy stands to various decay classes and at various heights of open canopy
stands.

While the size and class of the roosting snags may have differed from west to east,
snag species selection did not. Grand fir was used significantly more than availability at
both study sites (Tables 6,7). It was the only species of snag used more than expected

from a random model. While the abundance of grand firs decreases as a function of the

39

distance east of the Cascade crest, long-legged myotis continued to select grand fir at the
east site. It is unclear, however, whether a reduced abundance of grand fir has any effect
on population size. At Ormsbee’s study area (1997), grand fir was not available and these
bats primarily selected Douglas fir. However, when given equal abundance of Douglas
fir and grand fir at the present study area, this species selected almost exclusively grand
fir at the west site and selected grand fir more than expected at the east site. Rabe et al.
(1999) found that this species used ponderosa pine exclusively in northern Arizona, but
his site also lacked grand fir. When grand fir and ponderosa pine both exist in a
landscape, Myotis volans used ponderosa pine significantly less than expected (Table 7).
The selection of grand fir may be because of the particular way that grand fir
decays. Dead grand firs tend to display bark exfoliation that resembles shingles on a roof.
As thin plates of bark peel away from the trunk, they provide accessible crevasses that
these bats utilize for roosting. Douglas fir bark tends to stay tightly against the trunk until
it sloughs away in large blocks, limiting the amount of exfoliating bark available for bats
to use. In addition, it often leaves much larger spaces between the exfoliating bark and
the trunk than grand fir, thus possibly affecting the microclimate under that bark.
Ponderosa pine bark also appears to slough off in a similar manner. However, it should
be noted that Douglas fir and ponderosa pine snags that were used by these bats appeared
more similar in the way the bark was exfoliating to a grand fir than to most of the other
Douglas fir and ponderosa pine snags in the landscape. The roosts of the other snag
species that were used at the west site also had exfoliating bark that resembled grand fir.
It is difficult to quantify bark exfoliation for analysis. However, the outward

appearance seems to indicate that shingle-like exfoliating bark is one of the

40

characteristics that Myotis volans is selecting for. That may be related to the
microclimate that type of exfoliation provides, as well as, other factors including
protection against predators and the long-term stability of the roost-site. While any of the
tree species are capable of producing suitable roosts, it appears that grand fir, in general,
tends to provide the type of roost-site long-legged myotis are looking for more often than
the other snag species in this landscape.

In selecting a roost-site, the long-legged myotis appear to select roosts surrounded
by a higher local density of snags than at random sites in a stand (Table 3). This may be
because a bat is more likely to find the structure it is looking for if there are several snags
located together, rather than having to fly from snag to snag looking for the ideal site.
This hints at visual apparency theory, which states that the more clumped together a
certain feature is, the more likely that that feature will be apparent to the organism that is

utilizing it (Fenney 1976).

4]

MANAGEMENT IMPLICATIONS

Many forest managers on the east slopes of the Cascades have been focusing their
efforts on providing dispersed retention snags within harvest units as a way to keep
habitat in the landscape for wildlife (FEMAT 1993, R. Mendez pers. comm). While this
method may be successful for some species of wildlife, it does not appear to be a solution
for Myotis volans. This species shows a strong preference for late-successional forest
stands (Table 10). While this species appears willing to use aggregate retention patches
that provide the structure of late-successional forests, these patches likely lack the
microclimate regime of more continuous tracks of forest (Chen et a1. 1995). It does
appear as though leaving aggregate retention patches and using shelterwoods in clear-cuts
can mitigate the effects of timber harvests to some degree. But, when given the choice
between late-successional stands and aggregate retention patches, the bats avoid the
retention patches (Table 10). If given a limited amount of timber to protect from harvest,
it may be more useful for the management of this species to keep the timber connected in
relatively large blocks of late-successional forest, rather than spreading it out as retention
across the landscape.

In recent years, forest managers have been creating snags out of live trees for use
by wildlife (T. Brown, R. Mendez pers. com.) The long-legged myotis appears more
likely to select small pockets of snags rather than solitary snags (Table 3). In cases in
which forest managers wish to create additional snags for wildlife, it appears as though it
would be advantageous for this and other bat species to create small, localized pockets of

snags.

42

Several methods of snag creation are often used. Girdling kills the trees slowly
and leaves the snags intact, while dynamiting destroys the top of the tree. When choosing
a method, it appears as though girdling may be more preferable than blowing off the top
for this bat species in closed canopy stands. Intact snags of the early decay classes were
used almost exclusively at the west site and used nearly half of the time at the east site.
These tall intact structures may provide a more suitable microclimate than the shorter
snags that would result from having their tops blown off in closed canopy stands.

Another concern to forest managers on the east slopes of the Cascades is the
prevalence of grand fir. Grand fir is not considered an optimal tree species by forest
managers because of its susceptibility to fire, disease, and insect outbreaks. Historically,
when there was an active fire regime, much of the east slope forests were dominated by
fire-tolerant Douglas fir and ponderosa pine. Grand fir dominated stands were somewhat
infrequent in this area and tended to be located only in areas of locally high moisture or
humidity, such as north-facing slopes. For the most part grand fir was historically a
secondary component of these forests. Grand fir often remained in the understory until
large overstory trees fell and canopy gaps were formed allowing grand fir saplings to
grow quickly to occupy the canopy gaps. However, 100 years of fire suppression has
allowed grand fir to become one of the dominant canopy trees throughout the east slopes
of the Cascades. These grand fir forests are more susceptible to catastrophic stand
replacement fires than more fire-tolerant forests of Douglas fir and ponderosa pine.
Insects are a particular concern where spruce budworm outbreaks are the worst, because

spruce budworm seems to thrive on grand fir (CPTI, USFS, pers. com).

43

Despite these concerns, grand fir is an important wildlife species. This study has
shown that the long-legged myotis prefers grand fir snags as roost structures. In addition,
other bat species, small non-volant mammals, woodpeckers and many other bird species
and utilize grand fir extensively (Harris et. al 1982, USFS unpub. data). While forest
managers are attempting to return fire to the ecosystem and are attempting to control
spruce budworm outbreaks, managers should also attempt to maintain a grand fir
component to the forests. One suggestion to maintain the necessary grand fir component
while limiting the susceptibility of the forest to fire or insects is to space out grand firs
throughout a stand. When grand fir occurs in high densities, intraspecific competition
and disease are more likely to stress the trees. High stress brings higher susceptibility to
insects and disease and higher mortality. With higher mortality comes higher
susceptibility to fire (R. Mendez pers. com.) If grand firs are spaced apart in a stand to
limit competition, the risks of stand-replacement events decrease substantially.

The long-legged myotis appears to be a somewhat adaptable species. It is not
considered a common or abundant species on the east slopes of the Cascades, but it does
not appear to be rare either. It occurs in a wide range of habitats throughout western
North America. Even in a relatively small area, it appears to be able to utilize several
different forest types, including closed-canopy grand fir stands and open-canopy pine/oak
forests. However, despite this apparent flexibility, the species does appear to select roosts
that are located in relatively continuous tracts of forest. Much still needs to learned about
this species to assure its survival. First of all, solid population analysis techniques for
bats need to be developed in order to monitor the abundance of this and other bat species

through time. The microclimate requirements for day roosts need to be better understood

44

so that roosting behavior can be better predicted and incorporated into management plans.
Nighttime foraging patterns need to be assessed, so that managers can determine whether
forestry practices affect foraging success or energy use. Biologists need to determine
where individuals go to hibernate, so that managers can also protect this species during
that critically sensitive period of their lives.

However, despite the many gaps in our understanding of bat ecology, it seems,
based on the current information, that with careful stewardship of our forest resources,
that the long-legged myotis should be able to persist in the managed landscape of the east

slopes of the Cascade Range.

45

LITERATURE CITED

46

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