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AN EVALUATION OF STRIP CENSUS METHODS
FOR COTTONTAIL RABBIT POPULATIONS
IN SOUfl-iERN MICHlfiAN

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“is“: 50' The Degree of M. S.
MICHIGAN STATE ‘5' EVERSITY

Rainer Hans Bros-Re
1957

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AN EVALUATION OF

STRIP CENSUS METHODS FOR
COTTONTAIL RABBIT POPULATIONS
IN SOUTHERN MICHIGAN

BY

Rainer Hans Brooke
AN ABSTRACT

Submitted to the College of Agriculture
Michigan.3tate University of Agriculture
and Applied Science in partial
fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife A
1957 :.

Approved by .g;§€1;2%;t v? j<]7;;24é( Ki»\ :'

 

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ABSTRACT

Four strip census techniques, the King, Hayne, Kelker
and Webb methods have been most widely used for game cen-
susing. Investigators have found that strip censuses yield
highly variable results and require large sample sizes.

The present study was undertaken to determine the
reliability of the King, Hayne, Kelker and Webb strip census
methods for cottontail rabbit populations.

The field studies were conducted at the Kellogg Forest,
the Kellogg Bird Sanctuary, and the Kellogg Farm; the latter
two were treated as one area. These are part of the Mich-
igan State University Kellogg Station in southwestern
Michigan.

Strip censusing was begun on October 5, and continued
through December 9, 1955. Census lines were 75 yards and
100 yards apart, marked with white stripe of cloth.

Strip census population estimates were compared with
Lincoln Index estimates, generally considered to be
accurate. To obtain Lincoln Index values, rabbits were
trapped and marked; public and controlled hunting provided
the necessary second sample.

An artificial strip census model was set up to deter-
mine mathematical tendencies of the four strip census

methods. The artificial pepulation, based on field

 

 

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observations, was located and censused on graph paper;

these results are compared with the field study.

In 89.42 miles of census strips on both study areas,
26 rabbits were flushed. Strip census estimates ranged
from 5.5 to 48 percent of the Lincoln Index value.

Generally, the King strip census method gave the
lowest estimates and the Kelker method the highest and
most variable. As determined by the theoretical strip
census model, the Hayne method gave acceptable estimates,
although values were also low in the field study.

Apparently, the extremely low estimates in the field
are due largely to behavior patterns of the cottontail
rabbit, such as erratic flushing and a tendency to "hole

up during cold weather.
From the present study, it seems apparent that strip
census methods are not suitable or practical for measuring

cottontail rabbit populations in southern Michigan.

 

 

    

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Ab

  

AN EVALUATION OF
STRIP CENSUS METHODS FOR
COTTONTAIL RABBIT POPULATIONS
IN SOUTHERN MICHIGAN

BY

Rainer Hans Brooke

A THESIS
Submitted to the College of Agriculture
Michigan State University of Agriculture
and Applied Science in partial

fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife
1957

 

 

 

 

 

 

ABSTRACT . . . . . . . . .
LIST OF FIGURES. . . . . .
LIST OF TABLES . . . . . .
INTRODUCTION . . . .
Background. . . . . .
Purpose of this study
ACKNOWLEDGEMENTS . . . . .
STRIP CENSUS TECHNIQUES .

The Kellogg Forest .

OF CONTENTS

The Kellogg Bird Sanctuary and Farm .

The Artificial Strip Census Model . .

RESULTS AND DISCUSSION . .
King Method . . . . .
Hayne Method . . . .
Kelker Method . . . .
Webb Method. . . . .

Effective Width of Census

General Discussion .
s UT'IMARY o c O o 0 0 o o 0
APPENDIX . . . . . . . .

Classification of Cover Types .

Computing Formulas and Some Caluculations

LITERATURE CITED . . . . .

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4.2
4.3
4.4

4.5

 

 

LIST OF FIGURES

Cover map of the Kellogg Forest study area,
showing vegetation types and locations of
rabbits seen during strip censusing . . . . . . . 9

Aerial photo of the Kellogg Forest study
area showing strip census lines . . . . . . . . .10

Damaged census line marker. Such damage,

probably by red squirrels, occurred repeat-

edly in some areas; some markers were com-

pletely removed . . . . . . . . . . . . . . . . 11

Cover type 02; open land with high grasses
and S ome bme. I O O O I O I O O I I O O O I O O 11

Cover type D1; second growth deciduous woods . . 12
Cover type D2; mature deciduous woods . . . . . 12

Cover type Cl; conifer plantations with open
understory . . . . . . . . . . . . . . . . . . . 13

Cover type 02; conifer plantations with closed
mderstory o o n c o o o o a u o o o o o o o O 0 13

Cover map of the Kellogg Bird Sanctuary-Farm
area, showing vegetation types and locations
of rabbits seen during strip censusing . . . . . 17

Aerial photo of the Kellogg Bird Sanctuary-
Farm study area, showing strip census lines . . .18

Methods used in locating animals and obtaining
census data in the strip census model . . . . . 23

Population estimates and confidence limits, 90
percent accuracy, for the strip census model . . 28

Strip census form . . . . . . . . . . . . . . . 44

 

 

 

 

 

 

 

 

 

LIST OF TABLES
I. CALCULATED FLUSHING DISTANCES AND NUMBERS
FOR EACH FLUSHING DISTANCE - STRIP CENSUS
MODEL 0 O C I O I O O C I O O I O I I O O O O O 21

II. STRIP CENSUS POPULATION ESTIMATES - KELLOGG
, - FORES T O O I O O O C O O O O O I O O I 0 U i D 25

III. STRIP CENSUS POPULATION ESTIMATES - KELLOGG
BIRD SANCTUARY-FARM AREA 0 o o o o n o o c o o 25

IV. POPULATION ESTIMATES - STRIP CENSUS MODEL . . . 26
VD WEATHER DATA - ELLOG'G‘ FOREST 0 n o a c c o o o 36
VI. WEATHER DATA - KELLOGG BIRD SANCTUARY-FARM AREA 36
VII. DATA USED TO MAKE STRIP CENSUS POPULATION ESTI-
MATES - KELLOGG FOREST AND KELLOGG BIRD SANC-
TUARY‘FARM AREA 0 o n o A c u c u o o o o o o o 45
VIII. STRIP CENSUS OBSERVATIONS - KELLOGG FOREST . . 45

IX. STRIP CENSUS OBSERVATIONS - KELLOGG BIRD
SANCTUMY‘FWI AREA. o o c o o o o c o o o o o o 47

 

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INTRODUCTION

Background

A number of strip census techniques, also referred to
as belt transect and cruising census methods have been
devised to measure animal populations.

In general, a strip census estimates the population
for a cruised strip of known length and computed width.
This pOpulation density is then applied to the remaining

portions of the area being censused.

 

Various modifications of strip censusing have been
developed by different investigators to meet varying
situations. These strip census methods differ essentially
in one respect; the technique used to determine the width
of the strip. V

In 1931, King (Leopold, 1933) developed a strip census
method for brooding ruffed grouse, in which the width of
the strip was determined to be twice the average flushing
distance of feigning hens. Fisher (1939) and Frank (1946)
also used this method to measure grouse populations;
Erickson (1940), and Krefting and Fletcher ’1941) applied
the King method to censusing deer.

Breckenridge (1935) developed a strip census method
to measure wren populations. He used the perpendicular
distance, at which flushing numbers showed a marked

decrease, to calculate the width of strip.

 

 

Colquhoun and Morley (1941) estimated the density of

birds in open areas by strip censusing during the Spring
season, when birds were prominent. They calculated a width
of strip based on the normal identification distance of a
bird species.

Webb (1942) censused showshoe hare populations using
the sine of the average flushing angle to compute an aver-
age perpendicular flushing distance, on which the width of
strip was based.

Kelker (1945) developed a strip census technique for
deer, in which perpendicular sight distances from the line
of travel are divided into belts. The belt in which the
number of obserVations shows a pronounced decrease marks
the edge of the effective width of strip.

Hayne (1949) showed that the average observed flushing
distance, as determined by King, is not a good estimate of
the average flushing distance of the true population, and
should not be used to determine the width of strip. He
proposed that animals be grouped according to flushing
distance, using the sum of these groups to estimate the
total population. This method has been used to census
ruffed grouse (Palmer and Eberhardt,1955). Hayne's modi-
fication of King's method will hereafter be referred to
as the Hayne method.

King's, Hayne's, Kelker's and Webb's methods have been
compared for censusing winter-lost deer by Robinette et

al;' (1954, 1956). They concluded that Kelker's method

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was best suited to censusing dead deer.

Applications of the latter four methods have been
generally used for most game censusing.

Characteristically, strip census methods yield highly
variable results and require large sample sizes, often not
feasible in a practical situation. These disadvantages
are indicated by Fisher (1939), Palmer and Eberhardt (1955)
and the present study.

Purpose of this Study

This project was undertaken to determine the relia-
bility of population estimates by the King, Hayne, Kelker
and Webb strip census methods for the cottontail rabbit,
Sylvilagus floridanus mearnsii (Allen).

Estimates by the Lincoln Index method, generally con-
sidered to give reliable results, were used as a comparison.
In order to get some idea of the theory involved in
strip censusing,ax1artificial strip census model, based
on field data was also made. Estimates obtained by the

model are discussed and compared with the field study.

 

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ACKNOWLEDGEMENTS

I wish to express my sincere thanks to Dr. George A.
Petrides of the Department of Fisheries and Wildlife who
helped develop the project and provided many suggestions. A

Deep gratitude is due to Dr. Don W. Hayne of the ~
Department of Zoology, the originator of one of the strip
census methods tested. His guidance has proved invaluable
in the execution of the study and the statistical analysis
of the data.

I am grateful to Hr. Roswell D. van Deusen and Mr.
Walter Lemmien, directors of the Kellogg Bird Sanctuary
and Kellogg Forest of Michigan State University, who went
out of their way to provide station facilities. Mr. van
Deusen has also done most of the photographic work included
in this thesis.

Grateful acknowledgement is due to Dr. Aelred D. Geis,
a Ph.D. candidate in 1956, with whom a part of this study
was completed. He provided useful suggestions, and the
guidance of a senior graduate student.

Thanks are due Mr. Norman Barry of the Kellogg Forest,
Mr. Allen England and Mr. Jack Gilbert of the Kellogg Bird
Sanctuary and others who helped during trapping and con-
trolled hunting.

I appreciate the financial support of a Michigan

Conservation Clubs Wildlife Journalism Scholarship

 

received in 1955, a Michigan State University Tuition

Scholarship for the school year 1955-1956, and a Michigan
State University Graduate Research Assistantship for the
school year 1956-1957o

Finally, I extend my sincere gratitude to my wife
who typed the manuscript, made suggestions, and above all

was a constant source of encouragement.

 

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STRIP CENSUS TECHNIQUES

The field study was conducted on two separate areas;
the Kellogg Forest, the Kellogg Bird Sanctuary and the
Kellogg Farm; the latter two, adjoining one another, are
treated as one area. These are part of the Michigan State
University Kellogg Station, a demonstration unit in
southwestern Michigan.

During the previous five years, Geis (1956) directed
a study on rabbit population dynamics on these areas as
research toward a doctorate degree. To obtain tagged-
untagged ratios for Lincoln Index population estimates,

a rabbit trapping and marking program during each fall
season had also been conducted. Since the Lincoln Index
estimates were useful to both studies, the writer worked
with Geis running the trap lines.

A description of the study areas and the techniques
used on each will be given under corresponding headings.
The methodology used in the strip census model will follow

in a separate section.

The Kellogg Forest

The Kellogg Forest area is roughly rectangular in
shape, and occupies about four-fifths of a square mile.

It is located in T15, R9W, Section 22.

 

The area is approximately bisected by meandering

Augusta Creek, flowing in a southerly direction (Fig. 2).
The land rises east and west of Augusta Creek and gives
way to rolling topography, characteristic of this part of
the state. Originally farmed, the land was soon abandoned
because of the unproductive nature of the sandy soils. A
small portion has been retained as farmland.

Purchased by W. K. Kellogg, the eroded land was cone
verted into a wildlife area and donated to Michigan State
University in 1931. Large conifer and hardwood tree plan-
tations were made, and various shrubs were planted with
the intention of improving wildlife habitat. The resulting
cover is a varied heterogenous patch-work of coniferous
and deciduous vegetation (Fig. 1, Fig. 4 and appendix
p.48).

Eighteen strip census lines were established, 100
yards apart. A surveyors compass was used, and lines
were marked with strips of white cloth (Fig. 4.1). The
18 strips were divided into three routes, so that every
third strip, and a total of six strips, would be covered
on each route. A coverage of all 18 strips, or three
routes was completed in three census days (Fig. 2).

Four complete coverages were made.

To equalize effects of time of day over all
the strips censused, direction of traverse for the last
two coverages was reversed.

Strip censusing was begun on October 5th, 1955 and

 

 

 

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Figure 1. Cover map of the Kellogg Forest
study area, showing vegetation types, and
locations of rabbits seen during strip
censusing.( 0’

Figure 2. Aerial photo of the Kellogg
Forest study area, showing strip census
lines.

 

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Figure 2

 

 

 

 

Damaged census line marker. Such
damage, probably by red squirrels,
occurred repeatedly in some areas.
Sometimes markers were completely
removed.

 

Cover type 02. Open land with
high grasses and some brush.
(Refer also to appendix p. 48)

 

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Cover type D ; mature

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Cover type C ; conifer
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Cover type C ; conifer
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ended.October 19th. Flushing distances recorded were
determined by pacing; angles were obtained by using a
protractor and field compass. Perpendicular distances
werecomputed using flushing distances and angles. A copy
of the form used to record all data is shown in Fig. 9

in the appendix.

Walking speed along strip census lines was approxi-
mately two miles an hour. Crossing the creek presented
a small problem; canvas gym shoes were finally selected,
which proved quite comfortable on warm days.

Weather data were obtained from a small weather sta-
tion maintained at the Kellogg Forest.

Rabbits were captured in wooden and metal traps, and
were marked with metal bands on the ears and picric acid,
giving a bright yellow color, on the tails (Geis, 1956).
Rabbits so marked were used to estimate the pOpulation by
the Lincoln Index method (Appendix p. 52).

The Kellogg Bird Sanctuary and Farm

The Kellogg Bird Sanctuary-Farm area includes approx-
imately four-fifths of a square mile of terrain similar
to the Kellogg Forest.

The location is T18, R9W, Section 8. The vegetation
of the Kellogg Bird Sanctuary, with a similar origin and
development as that on the Kellogg Farm, closely resembles

the latter in complexity. The Kellogg Farm consists

 

15

Chiefly of heavily pastured land with small patches of
wildlife plantings (Fig. 5 and Fig. 6).

One-fifth of a square mile, located in two separate
portions, was strip censused. To prevent disturbing the
migrating waterfowl on Wintergreen Lake, located centrally
in the area, the census lines were set back from the lake.
Fences, animal enclosures and public areas restricted the
censusing to more remote portions. Only those areas were
censused for which Lincoln Index trapping data were avail-
able.

Strip census lines were laid out in the same manner
as on the Kellogg Forest, with the exception that lines
were 75 yards apart. Line directions, restricted by
existing conditions were not consistent (Fig. 6). Census
lines divided into a west (Route 1) and an east (Route 2),
were run on the same or consecutive days.

Strip censusing began November 21, and ended December
9, 1955. Records were kept in the same manner as on the
Kellogg Forest. Weather data obtained at the Kellogg
Forest were used for the Bird Sanctuary-Farm area; the
latter is only a little over a mile distant from the
Forest. Trapping was carried out in the same manner
as on the Kellogg Forest.

The shot sample of rabbits used to compute Lincoln
Index estimates, were obtained by controlled collecting
(Geis, 1956). Sub-populations were estimated for both

route areas using the kill map, trapping map and the

 

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Figure 5. Cover map of the Kellogg Bird
Sanctuary-Farm study area, showing vege-
tation types and locations of rabbits
seen during strip censusing.‘ a“ )

Figure 6. Aerial photo of the Kellogg
Bird Sanctuary-Farm study area, showing
strip census lines.

 

 

 

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original data cards.

The Artificial Strip Census Model

The object of the strip census model was to obtain an
estimate of theoretical strip census characteristics by
approximating ideal field conditions on paper. This
idea was suggested to the writer by Petrides and Geis.

It was developed independently by Palmer and Eberhardt
(1955), who employed a strip census model using an arti-
ficial grouse population. The latter authors used only
the Hayne strip census method to estimate populations in
their model. In this study, population estimates for the
King, Hayne, Kelker and Webb methods are compared. The
original field data were obtained by Geis on the Kellogg
Bird Sanctuary.

From a sample of 61 observations by a group of hunters,
the flushing distances were divided into nine convenient
groups, the first eight at two yard intervals. A weighted
mean flushing distance, calculated for each group, was
assigned in order of increasing distance, to an artificial
population of 200 rabbits in the observed proportions.
(Table I).

Positions of the 200 rabbits were then located on
graph paper, approximating a 1000 x 2000 yard area, each
small square representing one square yard. A table of

random numbers Was used for this purpose, two sets of

 

 

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20

random numbers being used to locate each animal (Fig. 7).
To obtain Lincoln Index estimates, the first 160 animals
(80%) were considered marked. Census lines were then
located on the long axis of the graph paper and flushing
distances and angles were determined by intersections of
census lines with flushing distance circles. A protractor
was used to measure angles. Perpendicular distances were
readily determined by counting the squares, each side of a
square representing one yard.

Five strip census surveys were made approximating

a strip 100,000 yards in length.

TABLE I

CALCULATED FLUSHING DISTANCES AND
NUMBERS FOR EACH FLUSHING DISTANCE -

STRIP CENSUS

MODEL

 

21

 

Flushing Distance Weighted Mean No. in Percentage No. in
Class in yards Flushing class of Pop. class
i, Distance Pop. 61 Pop.200
1-2 yds 1.7 yds 11 18 36
3-4 3.3 13 21 42
5-6 5.3 10 16 32
7-8 7.3 9 15 30
9-10 9.8 6 10 20
11-12 11.7 4 7 14
13-14 13 l 2 4
15-16 15 4 6 12
17-50 28 3 5 10

 

 

 

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Figure 7

Methods used in locating animals and
obtaining census data in the strip
census model.

Legend:

Animal No. 16.

Marked.

Flushing distance, 28 yards.

Perpendicular distance, 7 yards.

Flushing angle 15°.

Location: Row 108, Column 72, Up 7, Right 3-

 

 

24

RESULTS AND DISCUSSION

Discussion of strip census results, including compari-
sons with the strip census model are presented in the
following six sections; the first four deal with the indi-
vidual tendencies of strip census methods, followed by two
sections on the effective width of strip, and a general
discussion. Reference should be made to the appendix which
includes a more detailed treatment of formulas presented
in the text. Selected calculations and data used to make
various estimates are also given in the appendix.

In 55.32 miles of census strips at the Kellogg
Forest, only 13 rabbits flushed. Strip census estimates
ranged from a minimum of 8 percent of the Lincoln Index
value by the King method to 48 percent by the Kelker method.
Thirteen rabbits were seen in 34.10 miles of census stripe
at the Kellogg Bird Sanctuary-Farm area. Strip census
estimates ranged from 5.5 percent of the Lincoln Index
value by the King method (Route 2 area), to 41 percent by
the Kelker method (Route 1 area).

It is apparent that the strip census estimates are
quite low; a part of the discrepancy seems explainable by
the inherent mathematical tendencies of the King, Hayne,
Kelker and Webb computing methods.

.‘

 

 

 

 

 

TABLE II

25

STRIP CENSUS POPULATION ESTIMATES - KELLOGG FOREST,
LINCOLN INDEX ESTIMATE WAS 311.

Data used to make estimates are given in
Tables VII and VIII in the appendix

 

 

 

Estimates King Hayne Kelker Webb No. of
Method Method Method Method Rabbits
Observed
Pop. Est. 1st Cov. 125.63 241.79 362.00 164.20 5
2nd Cov. 125.03 130.24 103.77 125.03 2
3rd Cov. 9.61 17.12 103.77 37.11 3
4th Cov. 45.25 48.93 44.54 68.12 3
Mean 76.38 109.52 153.52 98.61 3.25
Pop. Est. Total Cov'.‘ 30.91 109.48 181.00 42.88
Standard Deviation 58.36 100.22 141.76 56.90
Standard Error 29.18 50.11 70.88 28.45
magma“ as: 112a 22332 as;
TABLE III

STRIP CENSUS POPULATION ESTIMATES -
KELLOGG BIRD SANCTUARY-FARM AREA.

Lincoln Index Estimate was 54 for Route 1 area, 39 for
Route 2 area. Data used to make estimates are given in
Tables VII and IX in the appendix.

 

Estimates based King Hayne Kelker Webb No. of
on Total Coverage Method Method Method Method Rabbits
Observed
'Route 1 6.05 8.06 22.13 8.71 10
Route 2 2.13 2.75 13.90 2.94 3

 

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26

TABLE IV
POPULATION ESTIMATES - STRIP CENSUS MODEL
Known population 200, 5 surveys of 20,000 yds. each

Estimates Idncoln King Hayne Kelker Webb No. of
Index Method Method Method Method @3535;

 

Pop. Est. lst Survey 198.62 139.75 223.75 150.00 218.71 36
" 2nd Survey 232.00 112.22 185.55 300.00 195.94 29
“ 3rd Survey 203.63 103.93 143.30 450.00 210.53 28
" 4th Survey 182.86 118.78 187.80 350.00 207.79 32
" 5th Survey 169.41 89.91 162.15 200.00 191.49 18
Mban 197.30 112.92 180.51 290.00 204.89 28.60
Standard Deviation 23.62 .18.47 30.29 119.38 11.08
Standard Error 10.59 8.28 13.58 53.53 4.97
Deparffir; from 200 -1.35 -43.54 -9.74 45.00 2.44
Confidggc; Limits 219.86 130.59 209.43 404.02 215.48
“ w 174.74 95.25 151.60 175.98 194.30
No. of surveys re-

quired for 1;%
accuracy, 95 oonf. 2.55 4.76 5.00 30.12 .52

 

 

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Figure 8

P0pu1ation estimates and confidence limits,
90 percent accuracy, for the strip census
model.

 

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380

360

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32.0

300

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/ / ///////////// //////////////

 

 

 

 

Lincoln
Index ‘ True. Hg“;
P. glut-Ion Ha. “c
P Y
n\
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Hsam Q
Conjidunu.
Ls..;t. 90%
King
\
\

 

 

 

 

 

 

 

King Method

sz‘fl
XI
: Total area of censused tract
: Number of rabbits seen
Total length of census line
: Twice the average flushing distance

.0 H >< ts b
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3 Estimated total population
Refer also to appendix, p. 50.

In both field studies and the strip census model, the
King method gave the lowest estimates (Tables II, III, IV).
In the strip census model, the mean census estimate for
five surveys (Table IV) is 43.5 percent less than the true
population of 200. A project by Robinette et a1. (1954,
1956) comparing the same strip census methods for winter-
lost deer, showed that the King method generally gave the
lowest estimates.

In theory, the tendency for the King method to give
low values can be attributed to the over-sampling of the
longer flushing distances, for which there is no correction
in the formula (Hayne, 1949). Hence, the population esti-
mate, based on a given number of observations for a wider
strip, is lower.

It is also interesting to note that the mean popula-

tion estimate, 76.38, of the four strip census coverages

 

30

at the Kellogg Forest is more than twice the estimate of
30.91 based on total coverage. This can be explained by
the increase in weight of shorter flushing distances in
estimates based on subdivided data; the ultimate end of
this process results in the Hayne method of calculation.
It is apparent that for any set of data, estimates by the
King method would vary considerably according to data-
group sizes.

From Table III it will be seen that population esti-
mates at the Kellogg Bird Sanctuary-Farm area are actually
lower than the number of rabbits seen during censusing;
this is because the area covered in the strips is greater

than the total census area.

Hayne Method

p:_€‘_(F1 .112. Ell-"'WEE)
2X 31 d2 d3 .
F1 - Fh : Numbers of animals observed to flush

at corresponding flushing distances.
d1 - dn = The various observed flushing distances.
The meanings of other symbols is the same as given

for the King method. Refer also to appendix p. 50‘

In the theory and mechanics of the Hayne method of
calculation, there seems to be no way to account for low
values obtained in the field study.

In the strip census model, this method gave the most

 

 

 

‘ .llv‘filh Ir

 

E ‘I‘WAIIIXII‘ I'll Elf . I‘llurnl‘l .d
Wilkiifllil \ h ‘ I 1 v in
, it- Illk1v.«r\\ul.u.l|i§4wl.' \\ _

 

31

satisfactory results (Table IV, Fig. 8). The mean estimate
of five surveys is 9.74 percent less than the true popula-
tion of 200, although the standard deviation of 30.29 is
next to the highest. The greater accuracy of the estimate
by the Webb method, compared to that by the Hayne method
is due to chance, governed by a constant relationship to
the King method. This is explained further in the text.

For the Kellogg Bird Sanctuary-Farm area, the popula-
tion estimates are lower than the number of rabbits seen
during the census. As mentioned above, this is the result
of a greater area covered in the strips than in the

censused tract.

Kelker method

 

P : if?

X!
i : Twice the effective width of strip.

The meaning of the other symbols is the same as given
for the King method. Refer also to appendix p. 51.

This method yielded the highest census estimates, both
in the field study, and in the census model (Tables II,
III, IV).

At the Kellogg Forest, the estimate of 181, based on
total field coverage is probably the best one because the
width of the strip is judged from the largest number of

observations. In the present field studies especially,

 

32

the small number of observations does not bear subdivision.
In the strip census model, the mean estimate for five
surveys was 45 percent higher than the true value of 200
(Table IV).

The standard deviation of estimates by the Kelker
method for the Kellogg Forest data and the model was the
highest of the four methods (Tables II, IV). Statistics
were not computed for the Kellogg Bird Sanctuary-Farm area
because the extremely low values would make them meaning.
less.

The high variability seems due to the subjective
approach of the method. By inspection, the width of the
strip is determined to be that distance on both sides of
the line of travel at which the number of observations
shows a marked decrease. (Appendix p. 51) This decision
is often difficult to make; an example taken from field

data follows.

Perpendicular Number of Accumulated Calculated Population

 

distance from rabbits number of density for estimate
the line of seen observations strip one
travel in yds. per strip yard wide
.33 5 5 15.15 196.54
.43 1 6 13.95 181.00
.66 l 7 10.60 137.58
1.00 1 8 8.00 103.77
2.00 1 9 4.50 58.37

Data used to make estimates are given in Tables VII

and VIII in the appendix.

 

 

 

ww—

w—g;

 

33

Rabbit density
for a strip
1 yd. wide

Perpendicular distance from the line of travel

It can be seen from the table and the graph that no
outstanding decrease occurs in the density of observations
from a perpendicular distance of .33 yard to 1.00 yard,
after which there is an actual increase; thus a different
decision would result in a considerable difference in
population estimates. To make the present population
estimate, the perpendicular distance of .43 yard was used.

It seems that the flushing behavior of rabbits is not
suited to the Operation of the Kelker strip census method,
1. e., a constant level of observations along a perpendi-
cular distance on both sides of the line of travel,

followed by a sharp decrease in number of observations, is

required.

Webb Method

AZ

P 2 -——-
xx Sin D

 

 

 

 

 

. (I..III a I. I l.-.,, uil cl. . 1.0.3. III-D'- . .l. - Inl...‘ u... HF. III!- 1 1 ‘ ‘ p tun-Elli:

s.’.ll'l(‘ . 1!. |br l . I

 

 

34

Sin D : sine of average flushing angle. The meaning
of other symbols is the same as given for the King

method. Refer also to appendix p. 51.

In the Kellogg Forest study, the two estimates by the
Webb method of 98.61 and 42.88 (Table II) bear a constant
Iaelationship to the two respective estimates by the King
Euethod.

Hayne (1949) pointed out that the theoretical mean for .
alry set of flushing angles is 32°42'. The sine of this i
tiieoretical angle is .54, so that estimates by the King
Inethod are doubled by the Webb method. This effect is
Bkiown in results obtained in the strip census model.

(frable IV, Fig. 8) The average of all flushing angles in

the model is 33° 27', the sine of which is .55; this does
Ilot differ significantly from the theoretical value.

Hayne observed that the deviation of flushing angles
from the theoretical angle may show the degree of randomness
of observations. Robinette et al.(1954, 1956) obtained
average flushing angles ranging from 42° to 48° for their
field study on winter-lost deer, indicating that a bias
‘was present in the strip censusing. Apparently, the
observer was not seeing animals ahead of him when they came
into visible range. Hayne suggested that the observer,
knowing his line of travel, looks more intently to the

sides than ahead, recording more of the larger angles.

Kellogg Forest data showed that the theoretical angle

 

 

‘qx‘:

w'

 

in

way

 

35

was exceeded considerably by an average flushing angle of
450 9' for all field observations. This seems to indicate
that. a similar bias as the one mentioned above, was present.
It should be noted, however, that in several instances the
1“lushing angle could not be determined accurately, because
the rabbit had been in motion for some time before it

was seen.

The extremely low population estimates obtained for
the Kellogg Bird Sanctuary-Farm area, lower than the number
of observations during censusing, are discussed above.

Weather data during strip censusing at the Kellogg
foI‘est and Kellogg Bird Sanctuary-Farm area are presented
in Tables V and VI“. There seems to be no significant
°°rrelation between the number of observations and weather
data. It is worth noting that on October 7, when Augusta
Creek was almost twice as high as usual, standing water
ektended several hundred gards on both sides of the
Creek in some sections. These areas were thus removed

t-emporarily as rabbit habitat.
Effective Width of Census Strip

To get an estimate of the width of census strip in
which theoretically all rabbits were flushed, the

following relationship was used:

F w - FA

 

L:__3
A L L

 

 

No. of Ave. Daily

WEATHER DATA - KELLOGG FOREST

TABLE V

 

 

 

Ilaxte Min. Precipitation % Cloud
Rabbits Fo Temp. Temp. in inches Cover
seen 8 am-5 pm. F0
Oct. 1 63 58 1.02 100
2 2 68.67 61 2.09 100
8 2 54 46 .22 0
9 1 65.50 36 0 0
10 l 63.33 37 0 0
11 0 56 36 0 0
l3 1 51 33 ..O3 0
14 O 48.67 27 0 0
15 2 45.67 27 0 33.33
17 2 50.33 45 .09 96.67
18 1 50 39 .05 95.83
19 0 46.33 35 .02 83.33
TABLE VI
WERTHER DATA - KELLOGG BIRD SANCTUARY-FARM AREA
No. of Rabbits Ave.
Ikzte , ail- Min. Prec. % Cloud
Rt' 1 Rt“ 2 Bewp? Temp inches Cover
New 21 4 33 22 o 100
22 l 38 28 0 100
Dec 1 1 20 5 _ o 100
2 32.33 23 .08 100
3 33.67 29 .06 100
4 28 26 .15 90
5 2 2 23 21 .03 100
6 2 21.33 14 O 0
7 1 20 o 100
8 29.33 15 O 100
9 1 22.67 16 O 80

36

 

*I—

.7VH wvw -—.... _——-—v—v w -_-—u-~r1’-' _

 

———~'-w.., Fwy-u...

HI :92"

 

37

W : Effective width of strip
A : Total area of censused tract

F : Fraction of the population seen during one
coverage of 18 strips

L : Length of census line in one coverage

For the Kellogg Forest area, the Lincoln Index value
crf 311 rabbits was used as the best population estimate;
tdie number seen during each coverage was converted into

a. fraction of 311.

First coverage: .2. : . 0161 etc.

 

 

 

311
Coverage Rt. 1 Rt. 2 Rt. 3 Total No. of Fraction
observations
let 1 2 2 5 .0161
2nd 1 1 O 2 .0064
3rd 1 0 2 3 .0096
4th 2 1 0 3 .0096
Total 5 4 4 13 .0417

 

The average fraction for all four coverages is:

‘0417 : .0104
4

Substituting in the above formula (Refer also to

 

 

Table VII) .

w - .0104 x 2525880 : 1.08 yds,
' 24340 """

For the Kellogg Bird Sanctuary-Farm area, the west

area (Route 1) had a Lincoln Index population estimate of

 

 

 

- '5‘,-

lllnulllr.‘ 5..

 

 

38

54 and the east area (Route 2), 39. The effective width of
census strip for the west area was calculated to be 1.90
yds., for the east area, .07 yds.

If these low values are an indication of the actual
effective width, the length of census line required to

give adequate population estimates would be beyond normal

Practicability. “I

General Discus sion

The highest strip census estimate for both study areas ’J
Was only 48 percent of the Lincoln Index value. It seems
Probable that some factors other than strip census mechan-
ics are responsible for the large discrepencies; estimates
Obtained by the model support this probability. The
Writer offers the following possible explanations, based
On observations in the field.

0n various occasions while running traplines in dense
Spruce and other conifer plantations, rabbits were observed
to escape readily under cover of low branches, making them
difficult to see. In Open areas, on the other hand,
rabbits often showed a tendency to “freeze". On one
occasion, at the Kellogg Forest, while crossing a very
promising glade with a sparse tangle of raspberry vines
along a census route, no rabbits were flushed. With

object of perhaps flushing a reluctant rabbit, the glade

was thoroughly covered, and a rabbit flushed less than a

 

 

39

yard from the census line. A similar incident occurred
diaring a strip census on the Kellogg Farm. Another person,
twealking several yards behind the writer, saw a rabbit
VVklich had not been flushed, next to the census line.
Another peculiar behavior pattern was observed during
‘tkie late fall and winter rabbit hunts on the Kellogg Bird

Sanctuary-Farm area. Patches of shrub cover and conifer

Iilantations, often hundreds of yards long, were driven

Iby'a line of hunters. As a precaution, several men were

satationed at the edges and far end of coverts, to inter-
<3ept rabbits that might break out. At the beginning of
Tune shooting period, rabbits broke cover only when
trunters had reached the end of the patch, but later
IPabbits were observed to break cover as much as a Quarter

(of a mile ahead of the line of guns. These rabbits were
Ilot seen by hunters in the line.

During particularly cold days in a comparitively
‘warmer period, rabbit activity was reduced and cover was
sought in brush piles and burrows. This could be plainly
seen by following tracks in the snow, and is a fact well
known to any rabbit hunter.

The behavior patterns mentioned above would result in
a decrease in numbers of rabbits seen in the census strip
and hence, a decrease in strip census population estimates.

From the present study, it seem apparent that strip
censusing is not suitable for measuring rabbit populations

in southern Michigan. It is possible that strip censusing

 

«a .. r.

 

 

a! 1.1.:1 I

 

 

could give an index of population abundance; however,

indices can be obtained with less labor and effort.

 

 

41

SUMMARY

In 55.32 miles of census strips at the Kellogg Forest,
<>nly 13 rabbits were flushed. Strip census estimates
xeanged from a minimum of 8 percent of the Lincoln Index
\ralue by the King method to 48 percent by the Kelker
Inethod. Thirteen rabbits were seen in 34.10 miles of
(zensus strips at the Kellogg Bird Sanctuary-Farm area. ~
Stiip census estimates ranged from 5.5 percent of the I
Ldncoln Index value by the King method to 41 percent by
‘the Kelker method.

Generally, the King method gave the lowest estimates
followed by the Webb and Hayne methods; the Kelker method
yielded the highest and most variable estimates. From a
theoretical viewpoint, the Hayne method gave the most
valid results, judging from the strip census model.

The effective width of strip, calculated from the
relationship of the fraction of the total pOpulation seen
during strip censusing, to the area censused and the
length of the census route, was small for both study
areas. Values ranged from .07 yard to 1.90 yards.

None of the strip census estimates obtained in the
field were higher than 48 percent of the Lincoln Index
value. Possible explanations for these low estimates
include erratic flushing tendencies, "holing up" during

cold weather, and rabbits escaping unseen by the observer.

 

*"w-n- -

 

42

The present study indicates that strip censusing is
not suitable or practical for measuring cottontail rabbit

p Opulations in southern Michigan.

 

 

 

 

 

 

 

 

43

 

APPENDIX

 

 

 

 

.3].sz _

Figure 9

no A m
J 5! 1 3.9L. 3.1.! .n
w U " v H
R ,. _ u k
4 n _ l
, M w u i
M m m
., H ,e . m
u, . n
no . _, .
._ s ‘
i3... 1”... E.» m 1
n. . ,
C.” . . W
on n w _ w
u- _ _ .. W
1.1. uIH, s _ _
ii. is r3...” ixw

t-l VLJ
|
Lu-

V
V, -. 4 m..-“ -n

,
:5:

TC

,1;
bug

Ti

1
A

i _._ ~..y_._....__.._ ,

I
,
.
l
.
A

 

é

!

. _
. _
. _
. .
. a
. .
.4 _
a .
i .
i .
. _
i. v
i a
t .91 ll}... ‘1'?

 

 

!

 

._ ._ ..___. .,~.A»—v.“_.¢

..:.'.I.I.|il'lx

)vvllll..ri1lllv j.

_.._.___.__.._.K

I 1.1Lrlll t. .

 

 

 

.. . .rltml‘lrfluautI nuhlt

 

 

DATA

TABLE VII

45

USED TO MAKE STRIP CENSUS
POPULATION ESTIMATES

KELLOGG FOREST AND KELLOGG BIRD SANCTUARY-FARM AREA

 

Kellogg Kellogg Bird
Statistic Forest Sanctuary-Farm
Area (sq. yds.) 2,525,880 270,000 West, Rt. 1
353.440 East, Rt. 2
Length Rt. 1 (yds.) 7.920 3,268
" Rt. 2 " ' 7,920 4,236
" Rt. 3 " 8,500
Total coverage Rt. 1 (yds.) 31,680 26,141
" " Rt. 2 " ’ 31,680 33,890
" " Rt. 3 " 34,000
Total, all routes (yds) 97.360 60,031
" " " (miles) 55.32 34,11

 

 

 

 

 

 

'J‘

 

 

 

TABLE VIII

STRIP CENSUS OBSERVATIONS - KELLOGG FOREST

Observation Route Strip Flushing

Perpendicular Flushing

 

j No. Distance Distance (yds) Angle
l (yds.) in degrees
{ 1 1 a .33 .33 90 !__T
2 2 a 2.00 2. 00 90 ‘9‘ 1
3 2 e 2.66 0 0 E
4 3 d 3.00 2.60 60 a ‘
5 3 r 2.33 .43 10 {:3
6 1 d 1.00 1.00 90
7 2 b .66 .66 90
8 l e 28.30 0 0
9 3 e 16.00 0 0
10 3 a 4.30 3.06 45
ll 1 d 3.33 2.33 45
12 l b 2.33 O 0
13 2 c 4.66 4.60 80

 

TABLE IX

 

47

STRIP CENSUS OBSERVATIONS - KELLOGG BIRD SANCTUARY-FARM AREA

Observation Route

Strip Flushing Perpendicular Flushing

 

No. Distance Distance (yds) Angle
(yds.) in degrees

1 1 e 6.00 2.53 25
2 1 e 8.00 8.00 90

3 l e 6.66 6.27 70
4 1 f 5.00 4.98 85

5 1 d 4.00 .70 10
6 l f 4.33 4.33 90
7 1 e 14.00 0 O

8 1 J 4.33 O 0

9 2 b 13.00 9.19 45
10 2 b 5.00 5.00 90
11 1 e 22.00 9.30 25
12 1 g 11.00 7.77 45
13 2 b 4.00 .35 5

 

 

 

 

 

 

48

Classification of Cover Types

The average maximum visibility, as used below, is

that distance at which rabbits could still be seen with

reasonable ease, by the observer during late fall.

01

02

D2

Open land with low, sparse grasses, ploughed
fields. Average maximum visibility, 80 yards.
Higher grasses, some brush. Cornfields. Ave-
rage maximum visibility, 40 yards.
Representative plant species: Red osier dog-
wood (Cornus stolonifera), gray dogwood

(Cornus racemosa).

 

Brushy. Heavy growth of woody vegetation.
Average maximum visibility, 4 yards. Repre-
sentative plant species: Tartarian honey-

suckle (Lonicera tartarica), red osier dog-

 

wood (Cornus stolonifera), sassafras

 

(Sassafras albidum).

Second growth deciduous woods. Average max-
imum visibility, 30 yards. Representative
plant species: Large-toothed aspen (Populus
granidentata), quaking aspen (repulus tremu-
loides), choke cherry (Prunus Virginians).

Mature deciduous woods. Average maximum
visibility, 40 yards. Representative

plant species: Black cherry (Prunus serotina),

 

black oak (Quercus velutina), red maple

 

 

 

 

 

 

 

 

Ci

C2

49

(Acer rubrum), white oak (Quercus alba).
Conifer plantations, Open understory. Average
maximum visibility, 15 yards. Representative
plant species; White pine (Pinus strobus),
jack pine (Pinus Eaggsiana), red pine (Pinus

resinosa).

 

Conifer plantations, closed understory, dense
growth of foliage near the ground. Average
maximum visibility, 4 yards. Representative

plant species: Norway spruce (Picea abies),

 

Tamarack (Larix laricina).

 

 

 

“VIM

 

 

(

W,

//
‘\

1

9

l

1

50

Computing Formulas
and Some Calculations

Kipg Strip Census Method

: Total area of censused tract
P: _

X!

No. of rabbits seen

Total length of census line

K N N P
n

Twice the average flushing
distance.

P 2 Estimated total population.
This is the formula and symbolism of the King Method
used by Fisher (1939).

Iiaype Strip Census Method
The original formula, as given by Hayne (1949), is:

m; a .4. .12 32mg.)
‘13

2L d1 d2 dn
Nt 2 Estimate of total population per unit
area.

L 2 Length of observers path.
d1 - dn= The various flushing distances observed.

F1 - Fn= Numbers of animals observed to flush
at corresponding flushing distances.

C : Conversion factor for area.
This was changed to:
2: _A..(.F'1_ 3.2. 32......31.)
2x d1 d2 d3 dn
where the meaning of symbols in brackets was retained,

and others were changed to symbols described for the King

method.

 

 

 

51

Kelker Method

 

The original formula given in the notes to University
of Michigan students is:
A - 8 x D x M
11 x H

A : Acres/animal

Flushing distance of farthest zone
which does not show a significant
decrease in numbers seen.

H : Number of animals seen in included 3

zones.
This was changed to: g;
P: __..AZ'
XI

I : Twice the effective width of strip.
Meaning of symbols other than Y is the same used in
the King Method.

Webb Method
The original formula given by Webb (1942) is:
P: .....______._Az
2X! Sin D
D : Average flushing angle in degrees.
Y 2 Average flushing distance.
The symbolism used is the same as that in the King
Method with the exception of D and Y.
The symbol D was retained and I was used to include

2! 1v1:P:__é_z._—_
’8 n6 xxsmn

 

Lincoln Index Estimates

 

Kellogg Forest

Total Population = Number Shot in Sample
Total Number Marked Number Marked in Sample
143 Rabbits were marked preseason

176 Rabbits were bagged during the hunting season
81 Rabbits bagged were marked

.SL.Z 176 ; Total Population 2 310.7
143 E1 '—

 

Kellogg Bird Sanctuary-Farm Area

West Area, Route 1

East Area,

36 Rabbits marked
24 Rabbits were shot in sample

16 Rabbits marked in sample

; Total POpulation : 54.0

 

Route 2
25 Rabbits marked
14 Rabbits were shot in sample

9 Rabbits marked in sample

P : l4 ; Total POpulation : 38.9
fig " § =====

 

 

 

 

 

Standard Deviation & Standard Error

 

2x2 -1313

 

$2 : n

nil
S : V 55 X 2
8g : S

W n:

Confidgnce Limits

Population estimate for
one coverage or survey

Number of coverages.

i i (S; x t) i : mean population estimate
for total coverages or
surveys.

Geis (1952) "t" value for .30 and .10 and

n'ldofe

Number of Surveys Needed forggpecified Accuracy

2

n:__.2.5 n:
(d?) 2

v s:

a:

Number of surveys needed
Variance
The standard error desired

to obtain sufficiently
accurate results, expressed
as a fraction of the mean.
d: ;075 for 15% accuracy
and 95% confidence.

- Mean estimate for surveys.

s..-.,4" -

‘ r: -..m

Mi 1

L“

 

 

 

  

",' ii
90
A

A.

LITERATURE CITED

Breckenridge, W. J. 1935. A bird census method. Wilson
Bul., 47:195-197.

Colquhoun, M. K. and Averil Morley, 1941. The density of
downland birds. Journ. Anim. Ecol., 10: 35-46.

Erickson, Arnold B. 1940. Notes on a method for censusing
white-tailed deer in spring and summer. Jour. Wildl.
1461-0. ’ 4: 15-18.

Fisher, Lee William 1939. Studies of the eastern ruffed

grouse in Michigan. (Bonasa umbellus umbellus), Mich.
State College, Agr. Expt. Sta., Tech. Bul., 166: 1-46.

Frank, William John 1946. Ruffed grouse censusing in west-
central Connecticut, Trans. N. Amer. Wildl. Conf.,
19: 287-294.

Geis, Aelred D. 1952. A method for estimating adequate
sample size and confidence limits for strip census
data. Paper presented at Midwest Wildlife Confer-
ence, Des Moines, Iowa, Dec. 17-19, 1952. 10 pp. (mimeo.)

Geis, Aelred D. 1956. A population study of the cottontail
rabbit in southern Michigan. Ph.D. thesis, Mich. State
Univ., 184 pp.

Hayne, Don W. 1949. An examination of the strip census
method for estimating animal pepulations. Jour. Wildl.

Kelker, George Hills. 1945. Measurement and interpretation
of forces that determine populations of managed deer
herds. Ph.D. thesis, University of Michigan, 422 pp.

Kendeigh, S. Charles. 1944 Measurement of bird popula-
tions. Ecol. Monogr., 14: 67-106.

Krefting, Laurits W., and Jack B. Fletcher. 1941. Notes
on the cruising method of censusing white-tailed deer
in Oklahoma. Jour. Wildl. Mgt., 5: 412-415.

Leopold, Aldo. 1933. Game management. Charles Scribner's
Sons, New York, London, 481 pp.

  

 

 

 

 

777 7 ——~ V'v-fl—"Vr 'W—

 

55

Palmer, W. L. and Lee Eberhardt. 1955. ENaluation of the

strip census method for ruffed grouse. Paper presented

at Midwest Wildlife Conference, Lafayette, Indiana,
Dec. 12-14, 1955. 7 pp. (mimeo.)

Robinette, W. L., D.A. Jones, J.S. Gashwiler and C. M.
Aldous. 1954. Methods for censusing winter-lost
deer. Trans. N0. Amer. Wildl. Cano, 19: 511‘5250

Robinette, W. L., D. A. Jones, J. S. Gashwiler and C. M.
Aldous. 1956. Further analysis of methods for
censusi winter-lost deer. Jour. Wildl. Mgt.,

20: 75-7 .

Webb, W. L., 1942. Notes on a method of censusing snow-
shoe hare pepulations. Jour. Wildl. Mgt. 6: 67-69.

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