Social Behavior and Foraging

Ecology of the Eastern Chipmunk

(Tamias striatus) in the

Adirondack Mountains

LANG ELLIOTT

m

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 265
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Eastern chipmunk Tamias strtatus.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 265

Social Behavior and Foraging

Ecology of the Eastern Chipmunk

(Tamias striatus) in the

Adirondack Mountains

Lang Elliott

SMITHSONIAN INSTITUTION PRESS

City of Washington

1978
ABSTRACT

Elliott, Lang. Social Behavior and Foraging Ecology of the Eastern Chipmunk

(Tamias stnatus) in the Adirondack Mountains. Smithsonian Contributions to

Zoology, number 265, 107 pages, 52 figures, 30 tables, 1978.—Herein are described

the social biology and ecology of a field population of eastern chipmunks (Tamias

striatus). Spatial dynamics of the population are reviewed and correlated with

adult social behavior. Social behavior in the litter prior to dispersal is described

and mating dynamics of the species is discussed in detail. Data on foraging

behavior are provided, with especial emphasis on the energetics of food-hoarding

behavior. Finally, a theoretical framework is proposed that relates spatial and

temporal patterning of food resources to the social and spatial systems of the

eastern chipmunk.

OFFICIAL PUBLICATIONS DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea

cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Elliott, Lang

Social behavior and foraging ecology of the eastern chipmunk (Tamias striatus) in the Adirondack Mountains.

(Smithsonian contributions to zoology ; no. 265)

Bibliography: p.

1. Eastern chipmunk—Behavior. 2. Social behavior in animals. 3. Mammals—Behavior. 4.

Mammals—New York (State)—Adirondack Mountains—Ecology. 5. Mammals—New York

(State)—Adirondack Mountains. I. Title: Social behavior and foraging ecology of the eastern

chipmunk. .. . II. Series: Smithsonian Institution. Smithsonian contributions to zoology ;

no. 265.

QL1.S54 no. 265 [QL737.R68] 591'.O8s [599'.3232] 77-13218
Contents

Page

Introduction 1

Acknowledgments 1

Spatial Use in the Chipmunk Population 2

Adult Patterns during Spring and Early Summer 2

Methods and Materials 2

Study Area and Grid 2

Trapping and Marking 2

"Visual Capture" Method 2

Fine-grained Following 5

Time-Area Curves 5

Grid-Structure and Resolution 5

Results and Discussion 5

Burrow Location and Geometric Center 6

Home Range Size 6

Use-Intensity Distribution 9

Home Range Overlap 12

Symmetry of Home Ranges 13

Home Range Shifting 14

Summary 15

Adult Spatial Use and Juvenile Dispersal Patterns in Autumn ... . 16

Home Range Use during the Fall 17

Juvenile Emergence 20

Juvenile Dispersal and Home Range Formation 22

Summary 25

Social Behavior in the Chipmunk Population 25

Adults and Postdispersal Juveniles 25

Social Interactions among Adults 26

Spatial Dynamics and Analysis of Social Behavior 29

Adult-Adult Social Interactions 30

Concepts and Terminology 33

Differences Associated with Age and Sex 34

Adult-Juvenile Social Interactions 35

Special Situations of Social Interaction 36

Social Cooperation in the Population 37

Hidden Polarities in the Population 39

Summary 40

Predispersal Social Behavior in the Litter 41

Mating Behavior 51

Social Structure prior to Breeding Season 52

General Description of Mating Bouts 52

Male Participation in Mating Bouts 54

Dominance Hierarchies among Males 55

Fine Structure of Mating Bouts 56
V I

 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Page

Utilization of Home Range during Estrus 59

Mating Systems of Other Sciurids 62

Comparison of Chipmunk and Arboreal Sciurid Mating Dynamics . . 63

Foraging Dynamics in the Chipmunk Population 67

Habitat Analysis 67

Foraging Behavior 69

Autumn Foraging 69

Chipmunk Utilization of Tree Seeds 69

Food Hoarding Methods 70

Crown Foraging versus Ground Foraging 70

Climbing Ability of Chipmunks 72

Temporal Availability of Food Resources 73

Estimated Winter Hoard Sizes for 1974 74

Spatial Availability of Food Resources 74

Juvenile Food Begging 76

Winter Months 76

Spring and Summer Foraging 76

Emergence from Hibernation 76

Foraging on Overwintered Seeds and Sprouts 77

Trout Lily Bulb Utilization 77

Long Movements for Red Maple Seeds 78

Scatter-Hoarding Behavior 79

Other Food Items 80

Spatial Availability of Food Resources 81

Burrow Pilfering 81

Late Summer Inactivity 81

Dwindling Food Supply 81

Botfly Infections 82

Dynamics of Burrow-Hoarding 82

Structure of Burrows 83

Food Hoards 83

Factors Affecting Storage Span of Food 87

Food Storage and Energetics 88

The Spring Burrow-Hoard 90

Interspecific Competition for Food Resources 92

Discussion 94

Variability in Foraging Behavior 94

Food Robbing 95

Types of Food Items 95

Seasonality of Food Availability 96

Burrow Structure 96

Food Availability and the Burrow-Hoard 97

Food Resources Patterns and Spatial Dynamics 97

Literature Cited 105
Social Behavior and Foraging

Ecology of the Eastern Chipmunk

(Tamias striatus) in the

Adirondack Mountains

Lang Elliott

Introduction

The eastern chipmunk (Tamias striatus of the

family Sciuridae) is a common, diurnal, forestdwelling squirrel inhabiting most of eastern North

America, ranging from the states bordering the

Gulf of Mexico to the southern tip of James Bay,

Canada (Banfield, 1974). Major aspects of the easttern chipmunks' life cycle have been reviewed by

several authors (Jackson, 1961: 142-149; Banfield,

1974: 96-99; Lowery, 1974: 193-198). A brief summary of current knowledge follows.

Individuals of both sexes are solitary and sedentary, inhabiting underground burrow systems.

Home ranges are small, usually less than an acre

(0.405 hectare) in area. Feeding primarily on nuts,

seeds, and fruits of various tree species, the eastern

chipmunk transports food items in internal cheek

pouches into special chambers in its burrow, where

the food is stored for later use. In areas where

winters are harsh, chipmunks pass the colder

months inside their burrows. Chipmunks do not

put on fat prior to the winter hiberation period as

do other rodents, such as woodchucks (Marmota

monax) and ground squirrels (Spermophilus spp.).

Instead, they draw on burrow-hoarded food items

Lang Elliott, Xational Zoological Park, Smithsonian Institution, Washington, D.C. 20560.

to survive the inclement period. Warm spring

weather marks their emergence from hibernation.

Spring, summer, and especially fall are spent gathering and storing food. A late summer lull in aboveground activity is common to many populations.

Breeding may occur in the spring (February-April)

or in the summer (June-August), with litters emerging above ground in late spring (April-June) or in

early fall (August-October). No pair bonding occurs

between males and females, and male-female coalitions during breeding periods are tenuous. After

approximately 30 days gestation, females give birth

to young and nurse them in their burrows. Young

first appear above ground when about 40 days old.

They disperse from the natal burrow a week or

two later, thereafter taking on the solitary lifestyle

of adults.

ACKNOWLEDGMENTS.—Many people provided valuable help during my years devoted to this project.

I am particularly grateful to Tom Kilfoyle and

Hayden Tormey of Onchiota, New York, for providing inspiration and raw materials for many

phases of my study. I am very indebted to John

F. Eisenberg and Eugene P. Morton of the National

Zoological Park, Smithsonian Institution, for allowing me to pursue my research in an uninhibited

fashion, for critically reviewing this monograph,

and for granting me permission to use the facilities
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

at the Office of Zoological Research, National Zoological Park. Assistance during my sessions in the

field was provided by the faculty of Paul Smiths

College; their companionship and feedback made

my stay in the north woods enjoyable and profitable. Permission to work on state property and to

capture and mark chipmunks was granted by the

New York State Department of Environmental Conservation. Financial assistance was provided by the

Zoology Department at the University of Maryland

and a graduate fellowship from the Smithsonian

Institution. I wish also to thank D. H. Morse, D. E.

Gill, W. Schleidt, and J. Potter for critically reading portions of earlier drafts.

Spatial Use in the Chipmunk Population

Adult Patterns during Spring and Early Summer

This report reviews spatial dynamics of the eastern chipmunk (Tamias striatus) population on my

Adirondack study plot during the late spring and

early summer nonbreeding period. Herein, I characterize spatial use in the population for later correlation with social behavior and foraging ecology.

Further, I generate a base for the detection and

analysis of movement changes related to the appearance of mating behavior or to changes in the distribution of food resources (see "Social Behavior"

and "Foraging Dynamics").

Previous investigations by other workers into the

home range dynamics of the eastern chipmunk

have concentrated primarily on the total area utilized by individuals as revealed by mark-recapture

techniques employing live traps (Burt, 1940; Blair,

1942; Manville, 1949; Yerger, 1953; Tryon and

Snyder, 1974; Forsyth and Smith, 1973). Although

chipmunks are diurnal and are easily observed in

the field, most investigators (with the exception of

Ickes, 1974) have not used direct observation to

yield home range use data. Ickes supplemented

trapping data with field observation to obtain better measures of home range use. My studies have

relied entirely on direct observation to reveal spatial use dynamics, thereby avoiding biases related

to the effects of traps on animal movements (Hayne,

1949; Sanderson, 1966). I also developed techniques

for quantifying spatial use by direct observation

that were successful in detecting variations in useintensity within home ranges of specific individuals

over short time periods (less than 3 weeks.)

METHODS AND MATERIALS

STUDY AREA AND GRID.—I conducted this portion

of my study from early May to late June 1974 on

the Adirondack study plot (see "Habitat Analysis").

The study area (Figure 1) measured 91.5 X 91.5m

(2.07 acre or 0.838 hectare) and was divided into a

grid (using numbered stakes) consisting of 144

squares, each 7.63 m on a side (0.0143 acre or 0.0058

hectare).

TRAPPING AND MARKING.—I captured all chipmunks using the study area during early May,

shortly after their emergence from hibernation, in

Sherman design live traps baited with sunflower

seeds (Figure 2). I marked the chipmunks for individual recognition at a distance with Nyanzol D,

a commercial fur dye (Figure 3). I recorded no

emergence of juveniles on the study plot during

this portion of my study, thus analyses are not

complicated by the recruitment of individuals into

the population (see "Mating Behavior").

"VISUAL CAPTURE" METHOD.—I began observation of home range utilization in mid-May from a

2-meter-tall portable stand resembling a life guard

91.5 m

•(300 ft)'

7-63 m

(25 ft)

w

%

/

J

•

r

)

E _

k

y

L

I

cK

m

wm

•Ik 1

)

4

c

1

c

T

I

i

7

FIGURE 1.—Schematic of 1974 study grid. The size of the

grid squares determines the resolution of spatial use measurements.
MIIVfRFR 2fifi

FIGURE 2.—Chipmunks were captured in Sherman design galvanized steel live traps baited with

sunflower seeds.

tower. I found interference with chipmunk movements to be minimal as long as I remained quietly

on the stand and refrained from making abrupt

movements.

To initiate an observation period, I placed and

mounted the stand at one of the nine positions

indicated in Figure 1. I allowed five minutes to

pass before gathering data, to minimize the effect

of my entry into the area. For 20 minutes, I then

monitored the movements of all marked chipmunks

visible from the tower. Then I moved the stand to

a neighboring numbered position, and, after five

minutes, I began another twenty minutes observation sequence. In this manner, I moved the stand

to all nine positions through a single observation

period lasting four hours. The total time spent

actually observing was 9(20) = 180 minutes or

three hours. I made no attempt to complete more

than one observation period during any particular

day in the field. I changed the sequence of movement of the stand for each observation period such

that after every three periods (days), each of the

nine positions was occupied for observation in the

morning, midday, and afternoon. This minimized

the effect of daily activity cycles on the data.

"Visual capture" (VC) data were collected in the

following manner. During each twenty minute

observation sequence, I continually scanned the

area surrounding the tower in search of marked

individuals. Whenever I spotted a marked animal,

I identified it (with the aid of binoculars), and I

recorded the grid square it occupied. Then I con-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 3.—Chipmunk with rear portions dyed black. All chipmunks utilizing the study site

were dyed with a commercial fur dye in specific patterns that allowed for recognition of

individuals at a distance.

tinued scanning for other marked individuals. If I

noted the same individual subsequently occupying

a different grid square, I recorded its presence in

the new square. I followed this procedure at each

of the nine positions. At the end of the observation period (day), I pooled data from all nine

localities. I then tabulated a list for each marked

individual, indicating which grid squares I noted

him to occupy during the entire observation period.

The data for a single individual can be visualized

effectively as a map of the study grid, with those

grid squares checked that the individual was seen

to occupy during the course of the observation

period.

This method allows single individuals to be visually captured in many different grid squares during the four hour interval, but it produces no measures of time spent by individuals in different grid

squares. However, by superimposing maps obtained

from several periods, a home range diagram reflecting time spent in each grid square is obtained. A

superimposed map indicates both the total number

of grid squares an individual was noted to utilize,

and the number of observation periods during

which the individual was seen to occupy each

square. The latter is a measure of time spent in a

grid square. An individual is more likely to be

spotted during each observation period in a highuse grid square than in a square it rarely visits.

The presence of the observation stand may result
NUMBER 265

in avoidance of the area immediately surrounding

the stand. To reduce this effect, I positioned the

stand at the common corner of four grid squares

at each of the nine positions (Figure 1). Thus, a

large portion of the four squares could be utilized,

even if the area immediately surrounding the stand

was avoided. Chipmunks, however, readily approached to within 3 meters of the stand, and, on

many occasions passed directly under the stand.

Observations at each of the nine positions were

not limited to the 16 grid squares surrounding

the stand (Figure 1). Thus, some overlap in the

scanning areas of the nine positions occurred. This

resulted in a tendency for centrally located portions of the grid to be under observation for a

greater time than peripheral areas. I reduced this

effect somewhat by directing more attention towards peripheral portions of the grid at each stand

location, such that approximately 60 percent of the

time (12 out of 20 minutes) I was scanning in the

direction of the periphery.

FINE-GRAINED FOLLOWING.—I gathered detailed

(fine-grained) information on home range utilization by selected individuals for comparison with

VC data. I obtained fine-grained (FG) data by

placing the portable stand within an individual's

home range, and visually following his above-ground

movements continually, through periods ranging

from one to eight hours. I recorded the time spent

in each grid square during these sessions. I conducted sessions at different times during different

days to minimize the effects of activity cycles. I positioned the stand at a different location during

each session. I attempted to gather from 8 to 15

hours of data for single individuals, and to spread

observations over a period of five or six days.

I then constructed for each animal a map indicating all grid squares visited and the total time

spent in each square. These maps, which represent

actual home range utilization levels, were compared

to maps obtained by the more indirect visual capture method.

TIME-AREA CURVES.—I extracted curves for each

animal demonstrating the cumulative increase in

home range area with increased observation time

from both the VC and the FG data. These curves

help clarify the value of spatial use diagrams in

understanding spatial use dynamics and estimating

home range size.

GRID-STRUCTURE AND RESOLUTION.—I did not

monitor variation in use-intensity within grid

squares. Thus, the size of the grid square sets limits

on the resolution of movement data. I chose the

7.63 X 7.63 m (25 X 25 ft) squares in light of a

pilot study on chipmunk movements carried out

on the study area during June of 1973. This size

allowed the collection of data without extreme

difficulty, and, at the same time, yielded enough

resolution to be useful in home range description.

RESULTS AND DISCUSSION

I gathered fine-grained home range data on two

resident females. Figure 4 depicts the home range

of 9 22 in mid-June and early July. I followed

9 22 for a total of 809 minutes during the period

from 11 June to 18 June, observations occurring

during seven sessions conducted at different times

during five different days. I followed 9 22 for another 799 minutes on three days in July, shortly

after $ 22 had passed through an estrus period and

breeding behavior had subsided (see "Mating Behavior"). Since home range use-patterns were similar for the two time periods and no home range

shifting was apparent, I lumped data over the

periods to form a composite map, representing 1608

minutes of following (Figure 4). On 10 June, I

followed 9 30 for a total of 8 hours from 10:00

A.M. to 7:00 P.M. These fine-grained data are included in Figure 5.

The values presented in each grid square in Figures 4 and 5 represent the total number of minutes that each square was occupied during the

observation intervals. Home burrow entrances are

included on the maps, along with geometric centers of activity. Geometric centers were calculated

after Hayne (1949) by summing along an X and Y

axis and computing the location of the median

along each axis.

I ran 14 separate observation periods, each on

separate days, from 16 May through 12 June. These

periods revealed visual capture data on 20 marked

animals utilizing the study grid. Four individuals

had home ranges almost completely enclosed by the

grid. Data from these "top four" individuals (9 15,

cf 18, 9 22, 9 30) constitute the most sound home

range information. Eight individuals had home

ranges that were approximately half contained by

the grid. The other eight had home ranges that

barely overlapped the study grid.
I I

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

2 2 5 6

2 15 3 22

2 1 1 19 II 1 2 8 5

1 II 47 262839 4 4

4540731^6 7 8

24 236 & 9923 17 7

1 B 13 5013 5

1 4 13 4

a

60

50

30

20

10

/

/

0

d

1 1 2 II 2 12 18 6

1 1 3 7 3 5 8 12

2 2 II 1 3821 7

13 8 6039 2 1 5

17 9 9 IK?13I 5 22 22

7 264224 29 9

1 12 8 2 1 4

4

b

f 11,12,13,16,18 June

- ^

9,13,11* July

6 12 18

No. Hours of Observation

1 1 4 26 5 34B 6

2 2 2 22 18 4 7 1617

3 13 58 2766 60 II 4

5848B354 8 1 7 13

41 32 24B42302B3929

8 39 55 74 42 14

1 13 12 6 1 8

4

c

58 squares

24

FIGURE 4.—Home range maps and time-area curve for 9 22 (derived from FG following, numbers

in a-c represent total minutes spent in each grid square, see Table 2 for FG data): a, 809 minutes,

50 squares; b, 799 minutes, 53 squares; c, 1608 minutes composite of a and b, 58 squares; d,

time-area curve for c (area = cumulative total number of grid squares utilized). (Solid circle =

burrow; circle with x = geometric center.)

The maps of home range use derived from the

VC method are depicted in Figure 6. Home burrow

locations are included on the maps where they are

known. I calculated geometric centers (Hayne, 1949)

for the "top four" and these are included on their

respective maps. I did not quantify movements

beyond the limits of the study grid. However, I

noted high-use areas off the grid and indicate them

on the home range maps with X's; this helps provide more realistic representations of home ranges

of peripheral individuals.

BURROW LOCATION AND GEOMETRIC CENTER.—In

Table 1, I compare the locations of geometric centers calculated from the FG data (Figures 4, 5)

and the VC data for the "top four" (included in

Figure 6) with home burrow locations. The maximum deviation recorded was 5.5 m ( $ 30-VC, Table

1) and the average fell at 3.1 m. Compared to the

total extent of home range movements indicated

in the home range maps, these deviations are not

great. These data indicate that home burrow locations may be used as a rough estimate of the

geometric home range centers for individuals on

the Adirondack study plot. This simplification is

used in the analysis of the data (see "Social Behavior").

HOME RANGE SIZE.—The total home range areas

calculated from either FG or VC data (Table 2)

are dependent upon observation time; increased

observation time leads to an expansion of the estimated home range limits. Time-area curves are invaluable in determining the adequacy of home

range area estimates.

Figure 4 includes a time-area curve showing cumulative home range increase over 1608 minutes of

FG following of $ 22 (composite of following in

mid-June and early July). Note that rapid increases

in apparent home range area occurred during the

first seven hours of following with substantial leveling beyond that point. Seven hours produced a
NUMBER 265

1 5 5 1

Z 5125 I

9 77g8Z S 6

7 51 33 25 II

4 25 28 4 8 5

6 3

« burrow entrance

= geometric center

26 squares

1 2 3 4 5 6 7 8

D No. Hours of Observation

FIGURE 5.—Home range map and time-area curve for 9 30

(derived from FG following, numbers in a represent total

minutes spent in each grid square, see Table 2 for FG data):

a, 491 minutes, 26 squares; b, time-area curve (area = cumulative total number of grid squares utilized).

home range area measurement 76% of the total

area measured after 24 hours of following. The

total area utilized during 799 minutes of following

in early July was 0.76 acres (0.31 ha), while the

composite of both periods of following produced

a total home range of 0.83 acres or 0.34 hectares

(Table 2).

Although extreme increases in 9 22's home range

area with increased following time would have

been doubtful, the time-area curve does indicate

that some increase would have been likely. The

0.83 acre (0.34 ha) value, therefore, represents a

minimal home range area for 9 22 during the

spring and early summer period.

The time-area curves derived from VC data for

the "top four" individuals are included in Figure

7. In three cases 9 15, tf 18, $ 30), the curves show

significant increases through the entire 14 observation periods. This points to the dubious value

of using VC data to calculate actual home range

areas; the calculated values for 9 15, c?18, and

$30 (Table 2) are undoubtedly much lower than

the actual utilized areas during the spring and

early summer period.

The time-area curve for 9 22 (Figure 7) substantially levels, with 86 percent of the total area being

measured after only 5 observation periods. However, comparing 9 22's total home range area measured by FG following in early June (0.72 acre or

0.29 hectare, Table 2) with the VC estimate (0.53

acre or 0.21 hectare, Table 2), significant discrepancy is obvious. Fine-grained following is more

sensitive in the monitoring of total home range

area because short excursions to peripheral areas

do not escape the observer. The visual capture

method may miss these erratic excursions. In any

TABLE 1.—Correspondence of burrow locations and calculated geometric

home range centers derived from FG and VC data for individuals whose

complete home ranges are known

Individual

PG data

922

930

VC data

915

dO.8

922

930

Average

Date of

observation

Figure

reference

C correspondence

m (ft)

Jun Ik

Jul Jk

Jun 7k

May-Jun 7k

May-Jun 7I+

May-Jun 7k

May-Jun 7k

k.6

k.6

1.8

0.6

k.3

0.6

5.5

(15)

(15)

( 6)

( 2)

( 2)

(18)

3.1+2.1 (10.3+6.7)
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

T2

1211 2 1

3197 1 1

34 8,3 1 2

1 1 7?>6 2 2

22673 2

1 23 2

?22

915

1

1 1

53271

1 58«831

21 362

2 31 3

1 1 3

1

1 1

111 1

1 1

1 1 2

0*16

1 111

1 1

1112 11

2732

1 1 6 &7 7 5

2 3 3 83 7 6 3

11128341

1 261 1 1

2

1

1

1

2 1

1 31

31 1

2 * 4

1 2861

2

2

1 CT18

1

X X

» x

X X

X X

221

2

4 1

3

2

• = burrow Ipcation

° = geometric center

944

1

1 1 1

1 22 1

1 142 1

4 7-4 2 1 1

X X X X

0*60

1

1

3 2 2

2 3 1

1 1 1

2 12 3

2 1 1

1 1

1

1

1

1

2

2 1

2 1

2 3

1 1

1

X X XX X

X XX X

FIGURE 6.—Home range maps derived from VC data for all individuals utilizing study grid

from mid-May to mid-June of 1974. Burrow locations unknown for £37, £41, $60, $62.

Geometric centers are included for the "top four" individuals, whose ranges fell completely

within the grid (9 15, $ 18, $ 22, 9 30). Use of areas up to 15 m (50') off the grid is indicated

by X's to give a more realistic picture of home range use by peripheral individuals.

case, 14 observation periods were not sufficient to

estimate actual utilization by visual captures alone.

The time-area curve for eight hours (491 minutes) following of $ 30 on a single day is included

in Figure 5, along with the home range use map

for that period. The time-area curve levels by the

fourth hour of observation, achieving 92 percent

of its final value. Comparing $ 30's total home

range area derived from the FG following (0.37

acres or 0.15 hectares, Table 2) with the area calculated from the VC maps (0.66 acres or 0.27 hectares, Table 2), the discrepancy is opposite to what

one may have anticipated. My notes reveal that

9 30 was active during the entire 8-hour period

foraging on a superabundant food resource (trout

lily bulbs; see "Foraging Dynamics") that did not

require lengthy excursions from her centralized

burrow. The VC data cross-sectioned a larger time

period and revealed broader movements. This example points to the importance of conducting fol-
NUMBER 265

TABLE 2.—Total home range area calculated from FG and VC data (values arrived

at by multiplying the total number of grid squares noted to be utilized by an

individual times the area of a single grid square, 0.0143 acre or 0.0058 hectare)

Individual

PG data

922

930

VC data

915

c/18

922

930

Date and duration

of observation

1608 min total

809 min 11-13, 16, 18 Jun

799 miB 9, 13, 1^ Jul

1+91 min 10 Jun

Ik periods late Mayearly Jun

lk periods late Mayearly Jun

lh periods late Mayearly Jun

lU periods late Mayearly Jun

Home range area

acre (hectare)

0.83 (0.3U)

0.72 (0.29)

0.76 (0.31)

0.37 (0.15)

0.37 (0.15)

0.37 (0.15)

0.53 (0.21)

0.66 (0.27)

No. of

squares

58

50

53

26

26

26

37

k6

lowing sessions over several day intervals to alleviate

the effect of short term stereotypy in movement

patterns.

The data on home range areas (Table 2) are not

conclusive; they do, however, represent minimal

home range sizes and are ecologically significant

measurements. Taking into account the time-area

curves and projecting from the data in Table 2, it

is my feeling that actual home range utilization

areas of most individuals under study during the

spring and early summer nonbreeding period fell

between 0.5 and 1.0 acres (0.2-0.4 hectares).

Another ecologically significant measurement is

the maximum distance from home burrow recorded

for each individual during the movement investigations. These data are important in the analysis

of foraging dynamics (see "Foraging Dynamics")

because they offer evidence for the chipmunk's potential to intercept concentrated patches of food

resources in his habitat. Maximum distances derived from FG following and VC maps are summarized in Table 3. These distances were measured

directly from the home range maps presented in

Figures 4, 5 and 6.

Most individuals were not recorded at distances

greater than 45 m from their home burrows; the

average calculated from the data in Table 3 being

39 m. Of considerable interest are the two long

excursions by g 16 and ^24 (97 and 61 m, respectively), whose ranges were peripheral to the study

area. Both individuals spent most of their time

off the study area in the vicinity of their home

burrows (Figure 6). The long excursions by both

males were single forays into the center of my study

grid during which the males were tallied in many

grid squares. Both males subsequently retreated in

the direction of their burrows, retracing their initial

routes.

These observations point to the possibility that

some individuals periodically make long journeys

of nearly 100 meters out of their normal home

range confines. This could have far-reaching effects

on their ability to locate food resource patches.

Since the longest journeys were made by males,

they could have been sexually motivated; I do not

have detailed data on this point but no females

entered estrus in the study area until over a month

after I observed the male forays (see "Mating Behavior"). These two males also made long excursions during the fall nonbreeding period (see p. 19).

Additional data is presented (see "Long Movements

for Red Maple Seeds") concerning the location and

utilization of a concentrated resource patch by both

sexes at considerable distances from home burrows.

USE-INTENSITY DISTRIBUTION.—Studying the home

range diagrams presented in Figures 4-6 reveals

that use-intensity varies over the measured home

range area. Further, it appears in most cases that

use-intensity is highest in grid squares closest to

the centrally located burrows and that it decreases
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

40 9i5

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Number of observation periods (days)

1 2 3 4 56789X 5 111 2 13 14

Number of observation periods (days)

5OT

30

930

2 3 4 5 6 7 8 9 10 11 12 13 14

Number of observation periods (days)

2 3 4 5 6 7 8 9 10 11 12 13 14

Number of observation periods (days)

FIGURE 7.—Time-area curves for the "top-four," derived from the VC data (area = cumulative

total number of grid squares utilized).

toward the periphery of the ranges. To test for this

pattern, I constructed histograms showing the average grid square use-intensity in 7.63 m bands at increasing distances from the burrows.

Figure 8 depicts the histogram for $ 30 derived

from 491 minutes of following (Figure 5). The home

range diagram is included with concentric circles

drawn in to clarify the method of analysis. Individual grid squares were assigned to the band in which

the greatest proportion of their area lay. Figure 8

also depicts the histogram for 922 derived from

the composite home range diagram in Figure 4

(1608 minutes of following). The average grid

square use-intensity for both individuals is highest

in the band nearest the burrow and gradually drops

with increasing distance from the burrow.

The histograms derived from fine-grained following reveal actual use-intensity differences between

concentric bands. For further data, I have derived

histograms from the visual capture maps in Figure

6. The VC method indirectly produces use-intensity

information; these use-intensity values do not directly reflect actual use-intensity, although they do

indicate proper ranking.

In the composite FG map of 9 22 (Figure 4)

the range of grid square use-intensity values is 1

to 230, while in 9 22's VC map (Figure 6) the

range is only 1 to 10. This discrepancy results

because a maximum of one capture per grid square

was allowed per each VC observation period, thus

setting limits on the total range possible. The VC

data can still be used to give a general picture of
NUMBER 265

11

TABLE 3.—Maximum distances traveled from home burrows, (recorded directly

from home range maps in Figures 4-6, only when burrow locations were known;

FG = derived from fine-grained following; VC = derived from visual capture

maps)

Individual

Date of

observation

Figure

reference

Distance

m (ft)

PG data

922

930

VC data

tf 6

910

915

c?l6

dl8

922

d23

d2k

930

?kk

9^5

9U8

950

953

95U

Average.

Composite mid-Jun- k

early Jul 7U

One day early Jun 7^ 5

May-Jun 7^ 6

May-Jun 7k 6

May-Jun 7I+ 6

May-Jun 71+ 6

May-Jun 7^ 6

May-Jun 7k 6

May-Jun 7k 6

May-Jun 7I+ 6

May-Jun 7k 6

May-Jun 7k 6

May-Jun 7^ 6

May-Jun 7k 6

May-Jun 7I+ 6

May-Jun 7^ 6

May-Jun 71+ 6

k3

23

1+6

28

3k

97

30

30

35

61

k8

39

2k

30

21

3k

( 75)

(150)

( 91)

(no)

(319)

( 97)

( 97)

(115)

(200)

(156)

(128)

( 78)

( 97)

( 69)

(no)

(no)

39+18 (126+60)

100

80

20

77

28

25

19

6O8

?30-491min.

* = burrow

FIGURE 8.—Histograms (derived from

FG following of $ 22 and $ 30) depicting average use-intensity (minutes) per

grid square in concentric bands at increasing distances from the home burrow.

$ 22 -1608 min.

(50) (75) (25)

DISTANCE CLASSES
12

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

use-intensity differences, but the individual values

are not directly comparable to actual use-intensity

values.

A diagram derived from VC data of changes in

average grid square use-intensity with distance

from the burrow is presented in Figure 9. It includes the lumping of VC data from seven individuals (0*6, $15, c?18, 9 22, d*23, 9 30, 9 44)

whose burrow locations were known and whose

home ranges fell mostly on the study grid (Figure

6). The pattern of the grand average grid square

use-intensity in the concentric bands is the same

as in Figure 8, with use-intensity decreasing with

distance from burrow. Figure 9 also shows individual graphs for each of the seven chipmunks. In all

seven cases, the values correspond to the pattern

just described. I conclude from the data presented

in Figures 8 and 9 that average grid square useintensity decreases with distance from the home

burrow for chipmunks in this Adirondack population.

r

SJ (75)

DISTANCE CLASSES

30.5 •

(100) (f

FIGURE 9.—Graphs (derived from VC data on seven individuals; Figure 6) depicting average use-intensity (in VC's) per

grid square in concentric bands at increasing distances from

the home burrow. The values in the rectangles represent

grand averages for all seven chipmunks in each distance

class. Ordinant values (visual captures) are equivalent to the

average number of visual captures per grid square in each

distance class for each individual over 14 observation periods.

Note that in all seven individuals, average use-intensity decreases with distance from the burrow.

HOME RANGE OVERLAP.—Since intensity of grid

square use is greatest near the home burrow, a hypothetical centralized "core area" (Kaufman, 1962:

170-172) of activity for each individual can be

easily visualized. In viewing the VC home range

diagrams (Figure 6), it is apparent that considerable overlap in spatial use occurs between neighbors on the study plot. The extent of overlap is an

important ecological variable because it is a measure of the amount of habitat sharing by individuals in the population. A major question is whether

or not centralized core areas are exclusive of intrusions by neighboring individuals.

Figure 10 presents the distribution of home burrows on the study area during Spring 1974. Along

with Figure 6, it will help the reader to visualize

relationships between home ranges. Female 30's

home range was centrally located on the study grid

and all her nearby neighbors were marked individuals whose home burrows were known. She utilized a total of 46 grid squares during the 14 VC

observation periods; 45 of the 46 squares (98%)

were also used by one or more of her marked neighbors. One square she may have used exclusively was

located on the periphery of her range 36 m from

910

« 5 4

?53

rf-41

•

* 4 8

•

<?23

•

•

« 30

*15

$ 4 4

?22

(?62)

(rf-60)

?50 \-r

 15.3 « (50 ft)

FIGURE 10.—Burrow distribution on study area during spring

1974. Parentheses indicate that the burrow location for that

individual was estimated from his home range map.
NUMBER 265

13

her burrow and well beyond her hypothetical core

area (Figure 6).

Further evidence for the lack of exclusive areas

comes from an analysis of data pooled from the VC

observations. A total of 133 grid squares were noted

used by marked chipmunks during the 14 observation periods. Of these, 109 (82%) were shared by

more than one marked individual. Of the 24 exclusive use squares, 16 (or 66%) were located within

15 m of the periphery of the grid and were being

used by unmarked chipmunks that periodically

made excursions into the study plot. These data

indicate that exclusive use of space, at the resolution of 7.63 X 7.63 m squares (0.0143 acre or

0.0058 hectare), is not common. In fact, if more

VC data had been gathered, home range areas

would probably have increased and exclusive areas

gradually disappeared.

As a measure of the extent of home range overlap (Table 4), I calculated the average distance

to the nearest four neighbors for ^18, $22, and

$ 30 (all three were located near the center of the

plot) and computed the percent of total visual captures for each individual bounded by a circle with

a radius equal to that average distance, the center

of the circle being the home burrow location (approximately equivalent to the home range geometric center). The three values all fall above 75%,

indicating that most movements of a chipmunk

are bounded by the locations of neighbor's burrows

(although excursions beyond the home range centers of neighbors do periodically occur).

SYMMETRY OF HOME RANGES.—The general shape

of home ranges and the location of the home burrows can be approximated by drawing a line connecting the outermost grid squares in which individuals were seen. Such maps are included in Figure 11, derived from FG following of 9 22 and

S15-VC ? 22-1608min.FG « 30-491 min.FG

?22-VC ?30-VC

FIGURE 11.—Home range shapes. A line has been drawn

connecting the centers of the outermost grid squares used by

individuals. (FG data from Figures 4 and 5, VC data from

Figure 6; black dot = location of home burrow.)

$ 30 and the VC maps of the "top four" (9 15,

cfl8, $22, $30). All other individuals had portions of their measured ranges falling off the grid.

Note that in all cases the burrows are centrally

located and the use of space in all directions approaches equality.

Since spatial use has an intensity component, a

breakdown of time spent in different directions is

useful. I have already pointed out that average

grid square use-intensity is highest near the centralized home burrow, gradually decreasing toward the

periphery of the range. However, those measurements (Figures 8, 9) were reduced to a single spatial dimension. In two dimensions, the pattern is

more variable. Table 5 gives relevant symmetry

data by breaking the home ranges of $ 30 and $ 22

(derived from FG following) into four quadrants

(NW, NE, SW, SE) using the home burrow as the

center. In extracting data for Table 5, if the dividTABLE 4.—Home range overlap (see text for explanation of

computations)

Individual

Average distance to

nearest h neighbors

m (ft)

i of total

VC's within

measured area

d-18.

?22.

930.

19.3 + 2.0 (63.3 + 6.10 86

31.2 + 8.0 (102.5 + 26.3) 100

22.9 + k.5 (75.1 + 1U.7) 78
14

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE

Quadrant

9 22

SE

SW

NW

NE

9 30

SE

SW

HW

HE

5.—Symmetry of home ranges of $ 22 and

explanations of quadrants)

No. of grid

squares used

7.6

17

20

13.1+

7

6

7

6

Minutes

spent in

quadrant

191

1+33

368

616

12l+

11+5

139

86

$ 30 (see text for

Maximum

traveled

m

31.1+

51.8

52.7

1+0.5

22.3

22.3

22.9

22.9

distance

in quadrant

(ft)

(103)

(170)

(173)

(133)

( 73)

( 73)

( 75)

( 75)

ing lines fell across the grid squares, proportions

of the time values in the intersected grid squares

were calculated. Maximum distances were measured

from the burrow to the center of the farthest grid

square utilized in each quadrant. (Figure 1 shows

compass orientation.) Female 30's range (Figure 5)

is highly symmetrical, the measured parameters being nearly equal in magnitude within each quadrant. Female 22's range, on the other hand, has

some notable asymmetries, although the home

range map (Figure 4) evokes the appearance of

symmetry.

The VC maps for the "top four" produce similar

results; ranges appear roughly circular but differences in quadrant use and the apparent avoidance

of some grid squares is obvious (e.g., Figure 6).

Some individuals show deviations from the circular

pattern. Male 16 and o*24 both made long excursions into the center of the study grid. Unfortunately, the center of their ranges lay off the grid

and movements in other directions could not be

ascertained. Female 62, whose burrow was unknown

during the spring of 1974, seemed to have an

oblong-shaped range. Her burrow was located the

following fall (in Figure 10) in the center of her

range.

I conclude from the data that most home ranges

are roughly symmetrical in a two dimensional

sense, with burrows tending toward the center of

a circular home range. Admittedly, deviations from

this pattern do occur, masking somewhat the formalized pattern of the population as a whole.

HOME RANGE SHIFTING.—Critical in the study of

home range dynamics is some knowledge of the

stability of home range locations through time. The

eastern chipmunk utilizes an underground burrow

system in which it stores food, sleeps, and retreats

during inclement weather. Chipmunks within the

study area exhibited considerable burrow tenacity.

Table 6 lists those marked individuals that remained on my study area through 6-month intervals. I tallied all individuals by trapping and ascertained their burrow locations during May and

September of each year of study.

Of the 32 cases of rechecking burrow locations

included in Table 6, only 3 (9%) involved changes.

One of these (910) occurred when a neighboring

individual ($21) died, thus leaving a nearby burrow system vacant. Another ($ 22) occurred when a

mother gave up her burrow to her litter at weaning

time and moved to another burrow on her home

range. The third case (J2) involved a fall born

juvenile who was found residing in a nearby adult's

burrow (9 30) the following spring. The adult had

disappeared. The fact that some individuals disappeared from season to season may indicate long

movements to new burrows off the study area. However, I often wandered about in the forest surrounding the study plot and I never found evidence that

this was occurring. Disappearance, therefore, probably reflects mortality in the population.

Since chipmunks tend to utilize the same burrow

from season to season, definite limits are placed

upon their general home range use-patterns; all
NUMBER 265 15

TABLE 6.—Burrow tenacity ("Same" = location of the home burrow unchanged from the previous season; "Unknown" = burrow not located but

presence of animal determined in season before and after 1974 checking dates)

Fall 1973 Spring

Same1

Same

Same

Moved

Same

Same

Same

Same

Same

Same

d

1

 18

9 hd

9 1 *

9 h5

9 50

9 53

Fall 1971* Spring 1975

9 21.

cf32.

9 10.

d 16.

d 2l+.

9 30.

a 6.

9 15.

9 22.

Same

Same

Same

Same

Same Same

Same Same

Moved.3 Same

Same

Same

Same Same

Same Same

Same Same

Unknown Same

d 2 Moved^

d 8 Same

9 70 Same

d 71 Same

1

 Died in trapping accident mid-May

2

 Moved into 21'8 burrow.

3 Moved int o 10's nearby vacant burrow, leaving hers with her

newly emerging litter .

**• Moved int o 30's burrow.

movements radiate from the home burrow and gradual shifting of home range through space (as in

nomadic species) does not occur. Figure 4 presents

evidence for the stability of home range location

and use-intensity distribution from month to

month. Female 22 was followed for approximately

13 hours in mid-June and then for another 13 hours

in early July (Table 2). The home range shapes are

nearly identical for the two time periods and the

use-intensity distributions look very similar.

Short-term variations in use-intensity distribution

within the home range are common because chipmunks tend to concentrate their activities around

concentrations of food resources. Persistent use of a

particular area may last as long as several days,

followed by a switch to a new area (see "Foraging

Behavior"). Such switches may lead an investigator

to believe that home range location is shifting. My

data, however, indicate that chipmunks maintain a

single home burrow system and exhibit considerable

stability in home range use-patterns when viewed on

a long-term basis.

SUMMARY

Home range data from spring and early summer

1974 support the following statements concerning

spatial use on the study grid: {1) Home burrows are

centrally located in relatively symmetrical and circular home ranges. (2) Home burrows fall close to,

and serve as a useful approximation of, the home

range geometric centers. (3) Use-intensity per unit

area is greatest in the central portions of the home

range (near the burrow) and gradually decreases

toward the periphery of the range. {4) Overlap be-
16

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

tween the home ranges of neighbors is great, approximately 75% or more of an individual's time

being spent in an area bounded by the locations of

his neighbor's burrows. Although individuals may

be thought of as possessing a centralized "core area"

of activity, exclusive use of space is not common in

the population. (5) Chipmunks are sedentary and

most maintain the same underground burrow system from season to season. This burrow tenacity

has a stabilizing effect on home range locations and

general patterns of spatial use. (6) Total home

range area was difficult to measure; however, the

data do indicate that chipmunks on the study plot

regularly utilize areas of approximately 0.5—1.0

acres (0.2-0.4 hectare). Most individuals rarely travel

beyond 45 m from their burrow, but movements of

60-90 m do occur periodically. These long movements may be very significant since they allow the

location of scattered but concentrated patches of

food resources.

Figure 12 graphically depicts the points listed

above. The diagram, representing relationships in

three dimensional space, has been reduced to two

dimensions for convenience. I calculated 24.4 m as

the approximate average interburrow distance from

data presented in Table 4. It is my feeling that the

data allow the spatial dynamics of the adult, nonbreeding population to be viewed as relatively formalized in structure. The relationship depicted in

Figure 12 will serve as a foundation for analysis of

departures in movement patterns related to breeding activities, the emergence and dispersal of juveniles, and spatial and temporal fluctuations in food

GEOMETRIC CENTER

AND

BURROW LOCATION

DISTANCE

FIGURE 12.—Average spatial relationships between neighbors

in study area.

resources. Further, Figure 12 will serve as a core for

the analysis of social behavior within the study area

and for a theoretical discussion of the adaptive

nature of the chipmunk spatial system.

Adult Spatial Use and Juvenile Dispersal Patterns

in Autumn

I conducted this portion of the study from early

September to late October of 1973 and 1974 on the

Adirondack study area (see "Habitat Analysis"). In

1973, my study area measured 61.0 X 61.0 meters

(1.15 acres or 0.465 hectares). During 1974, I shifted

the plot and enlarged it to measure 91.5 X 91.5

meters (2.07 acres or 0.838 hectare). During both

years, I divided the study site into a grid consisting

of squares, each 7.63 meters (25 ft) on a side.

The relationship of the fall 1973 study area with

the 1974 (spring, summer, and fall) area is denoted

in Figure 13 in the home range map of $ 45. I captured all adult chipmunks utilizing the plot during

early September of both years. I attempted to capture all juveniles as they emerged, but many dispersed before I could trap them. I dye-marked all

captured chipmunks for individual recognition (see

P- 2).

I determined home ranges of individuals by the

visual capture method (p. 2). The portable stand

move-sequence was altered during 1973, but the

data for both fall periods are comparable and may

be in turn compared with the spacing data from

spring and early summer of 1974.

During the fall of 1973, I ran a total of 16 observation periods from 16 September to 24 October.

During the fall of 1974, I ran a total of 13 periods

from 29 September to 19 October. Emergence and

dispersal of juveniles (< 100 days old) occurred

from mid to late September of both years, most dispersal taking place before visual capture (VC)

determinations were begun. I gathered data on

these early phases of emergence and dispersal during my trapping procedures. I located the home

burrows of adults (and juveniles when they established home burrows later in the season) by observing food hoarding activities or the transport of

nesting material (crushed leaves) into burrows.

The home range use diagrams derived from the

visual capture method for the 1973 and 1974 fall

periods are presented in Figures 13 and 14. These

maps reflect spatial use by marked individuals
NUMBER 265 17

AC&

2111

1 21

332

3 44108 X

1 33IS7X

45511X

5837X

14331

2 2 3 1

2 1

1 11 1

1 23 111

12573221

12M 2

1 244 1

23

1 3

XXX

2 6126;

A9-21

1 ^2 2

5 3

1 552 1 3 4 11 7 2

1 3TW2t)

1 593

1

X

XX

XX

X

X

2 1

4 21 1 1

4 1 1 1 2

AC?23

XXX

5722

5878>4

688 11

1 35422

123 1 1 1121

AC?24

X

X

X

A?30

1

5 22

7tJ51

7941

4 3 5

J?25

22 1

452 11

1 562

4 1 2

JC?26

1 1 1

1 2 1 14 133

46351

1 1108 74 2

5BF ?

XXXX

X3732

X81 1

1 2

X XX

23341

1486351

255533

2 56 7 54

542 1 1 1111

1 3 1

•#45

FIGURE 13.—Home range maps derived from the visual capture method for

adults (A) and juveniles (J) utilizing the study plot from late September through

October 1973. (Solid circle = burrow locations; X = use of areas up to 15 m

(50 ft) off the study plot.)

through the peak period of food availability during

each of the two fall seasons when chipmunks were

actively involved in collecting and hoarding food

prior to the winter period (see "Foraging Behavior").

HOME RANGE USE DURING THE FALL

Relevant data concerning the analysis of the VC

home range diagrams are in Figures 15, 16 and

Tables 7-9. These data demonstrate that general

home range use-patterns during the two fall seasons

TABLE 7.—Maximum distances adults traveled from their home burrows during

autumn 1973 and 1974 (derived from Figures 13 and 14, respectively, only where

burrow locations are known)

Individual

Fall 1973

cf 6

9 10

9 15

9 21

9 22

cf 2k

9 30

Average..

Distance

m

1+8.8

1+5.7

20.7

28.0

Ul.l

1+9-7

27.1+

37.3+H.8

(ft)

(160)

(150)

( 68)

( 92)

(135)

(163)

( 90)

(123+38)

Individual

Fall 1971+

cf 6

9 15

cf 16

cf 18

9 22

cf 2k

9 30

9 1*

9 1+5

9 kS

9 50

9 6k

Average. .

m

1+1+.5

29.9

95.1

36.0

6U.6

31.1

2k.k

18.3

31.1+

32.0

22.9

38.7+21.1+

p

(ft)

(ll+6)

( 98)

(312)*

(113)

(118)

(212)**

(102)

( 80)

( 60)

(103)

(105)

( 75)

(127+70)

Made two long excursions

**Made single long excursion
18

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

37

2 17513

1 14 714

249233

16 21

A?30

4 1

1 663

58 2

332

1

1

341 2 5

3 4'

1 6f

3

1

»52

P71

1 1

JCfl2

1 2 2 Z 4 X

1 3 5

1 31

• « spri ng 1975 burrow

1

1

1

35

3491

34 1 11

14 1121

2

• • spring 1975 burrow

J931

31 11

14 1 1

1 41 ?

522 1 2532321

1 2 332

1111

1 2

2 .2 2 1 2 1 1*1 4 2 111121

322

23

J956

spring 1975 burrow

FIGURE 14.—Home range maps derived from the visual capture method for adults (A) and

juveniles (J) utilizing the study plot from late September through October 1974 unless otherwise noted. (Solid circle = burrow locations; X = use of areas up to 15 m (50 ft) off the study

plot.)
NUMBER 265 19

TABLE 8.—Home range overlap derived from Figures 13 and

14 (see text for explanation of computation)

DISTANCE CLASSES

FIGURE 15.—Average use-intensity (in VC's) per grid square

versus distance from the home burrow of six adults during

autumn 1973, derived from home range diagrams presented

in Figure 13 (see also Figure 9).

were similar to the patterns described for spring

1974. Further, these data add to the validity of Figure 12 as a summary diagram of the primary aspects

of spacing in the nonbreeding population.

Figures 15 and 16 are composite graphs indicating a gradual decrease in average use-intensity per

grid square with distance from home burrows for

adult individuals during both the fall of 1973 and

the fall of 1974. Data were derived from the VC

maps in Figures 13 and 14 for adult individuals

DISTANCE CLASSES

FIGURE 16.—Average use-intensity (in VC's) per grid square

versus distance from the home burrow for seven adults

during autumn 1974, derived from home range diagrams

presented in Figure 14 (see also Figure 9).

Individual

Fall 1973

9 10

Fall 1971+

9 15

cf 18

9 22

9 30

Average..

Average distance to

nearest 1+ neighbors

m (ft)

22.3 +

21.5 +

23.1+ +

20.3 +

21.6 +

3.9

2.1+

h.5

2.3

3-2

(73.3 +

(70.5 +

(76.8 +

(66.5 +

(71.0 +

12.8)

7.9)

l'.6)

10.6)

% of total

VC's within

area

80

87

67

89

87

82

whose home burrows fell within the study plots.

The gradual decrease in use-intensity is similar in

pattern to that demonstrated in Figures 8 and 9 for

the spring nonbreeding period.

Table 7 tabulates the maximum recorded distances of travel from home burrows for adults during the two fall periods. Again, the data resemble

those presented for the spring period {Table 3).

The average falls near 38 m and few individuals

were recorded moving distances greater than 45 m

from their home burrows.

The unusually long excursions recorded for cf 16

and ^ 24 during fall 1974 are interesting in that I

noted these same two individuals to make unusually

long movements during the spring period (Table

TABLE 9.—Minimum home range areas of adults

(see text for explanation of computation)

Individual

Fall 1973

d 6

9 10

9 22

d 2k

Average..

Fal l 197U

9 15

cf 18

9 22

9 30

Average..

Home

acre

0.6U

0.1+9

O.36

0.1+6

0.1+9+0.

0.33

O.36

O.36

0.37

O.36+O.

range area

(hectare)

(0.259)

(0.198)

(0.11+6)

(0.186)

12 (0.197+0.01+7)

(0.13*0

(0.11+6)

(0.11+6)

(0.150)

02 (0.11+1++0.007)
20

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

3). It is possible that these males are disposed to

roam over larger distances as compared to other

members of the population. During the fall of 1974,

food resources were superabundant on the study

plot (see "Foraging Behavior" and Table 23) and

did not warrant long forays from home burrows.

Further, I observed no signs of breeding behavior in

the fall population. The two males had home burrows off the study plot and the extent of their movements in other directions was not recorded.

Table 8 summarizes data on home range overlap

for the fall months. These data are derived from the

VC maps (Figures 13, 14) for those adults whose

nearest four adult or juvenile neighbors (and their

burrow locations) were known. The data are comparable to those presented in Table 4 for the spring

period (see p. 13). At least 60 percent, and an average of 82 percent, of the total number of visual

captures for an individual fell within an area

bounded by the home burrows of his nearest four

neighbors. Further, the average distances included

in Table 8 are similar in magnitude to those presented in Table 4. The values in Table 4 served as

a basis for organizing the distance axis in Figure 12.

Home range area data for the autumn are included in Table 9 for individuals whose movements

were mainly restricted to the study grid. I extracted

these measures by counting the total number of grid

squares used by each individual (see Figures 13, 14)

and totaling the areas of those squares. Since home

range area increases with observation time, these

measures represent minimum home range sizes.

These measures are of dubious value in discussion

of home range dynamics, but I include them here

for later comparisons of adult and juvenile home

range use within each fall season.

JUVENILE EMERGENCE

During 1973 and 1974, chipmunks on the study

plot exhibited a midsummer breeding season and

juveniles subsequently emerged into the population

during September. Table 10 lists the emergence

TABLE 10.—Emergence dates and fates of littermates for autumns of 1973 and 1974

Emergence

date

Fall 1973

11 Sep

12 Sep

13 Sep....

Fall 1971*

17 Sep....

18 Sep

2k Sep

2k Sep

Parent

9

9

9

9

9

9

9

15

22

10

30

15

kk

22

Litternates

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

J

9

d

a

d

9

9

d

d

d

d

9

o"

d

d

9

9

d

d

9

9

9

9

25

26

28

31

32

33

3k

35

36

37

k5

8

12

Ik

25

31

72

75

36

ko

66

70

Comments

Last seen 25 Sep

Utilized study grid

Last seen 27 Sep

Last seen 17 Sep

Utilized study grid

Last seen 17 Sep

Last seen 13 Sep

Last seen 19 Sep

Last seen 27 Sep

Utilized study grid

Utilized study grid

Utilized study grid

Utilized study grid

Last seen 29 Sep

Utilized study grid

Utilized study grid

Last seen 29 Sep

Utilized study grid

Utilized study grid

Utilized study grid

Utilized study grid

Utilized study grid

through

through

through

through

through

through

through

through

through

through

through

through

through

Oct 73

spring

spring

spring

spring

spring

spring

Oct Jk

spring

Oct 7k

Oct 7k

spring

spring

7k

7k

75

75

75

75

75

75

75
NUMBER 265 21

dates for litters of females on the study plot. The

dates refer to my first observation of juvenile activity at the natal burrow. The juveniles listed in

Table 10 comprise only those litter members captured and marked. Therefore, only minimum litter

sizes are suggested by Table 10. I estimate that one

or two juveniles from each litter dispersed before I

was able to trap and mark them.

Evident from Table 10 is considerable synchrony

in litter emergence between mothers. More data are

available for fall 1974 during the period from 17-28

September, when a wave of emerging juveniles was

evident. I captured a total of 33 different juveniles

during this period on, or in the area immediately surrounding the study plot. Of these 33, 11

emerged on the study plot and had known mothers,

hence were included in Table 10; the other 22

emerged just outside the study plot and had unknown mothers. Estimates of age upon emergence

may be derived by comparing the fall 1974 litter

emergence dates with the July 1974 estrus dates of

females within the study plot (see "Mating Behavior," Table 16). Estrus occurred in the 4-12 July

period (indicating synchrony in estrus for 1974),

and emergence occurred approximately 75 days

later during the 17-28 September period. Gestation

has been estimated at 31 days by other workers

(Smith and Smith, 1972); therefore, age upon emergence was approximately 44 days.

Table 10 also summarizes data concerning the

fates of juveniles that emerged within the study

plots. During the fall of 1973, 7 Juveniles out of 11

disappeared within two weeks after emergence, indicating a high level of dispersal off the study

plot and/or mortality. During the fall of 1974, a

greater proportion (9 out of 11) remained on the

study site through the fall interval. The greater

apparent survivorship of the fall 1974 juveniles

could be related to the larger size of the study plot

during 1974 and the superabundant seed crop available during that fall (see "Foraging Behavior,"

Table 23). Table 10 also includes data on survivorship to consecutive seasons, terminating with a final

survey of the study area in spring 1975.

The determination of which adult female is responsible for a newly emerged juvenile is complicated by several factors. First, dispersal from the

natal burrow occurs within two weeks after emergence. I experienced difficulty in capturing many

juveniles while they were still in the vicinity of

their natal burrows. During both seasons, juveniles

appeared to have dispersed by the time I began VC

observations periods (16 September in 1973, 29

September in 1974). Once dispersed, it became impossible to ascertain the natal burrow location of

an unmarked juvenile or to determine the identity

of its mother. Second, the behavior of mothers toward their litter at emergence time was variable.

Some mothers transported their young to burrows

near the periphery of their range prior to emergence. Others allowed their litter to emerge from

their home burrow and shared it with them during

the predispersal stage. Further, I observed one instance where a mother ($22) gave up her home

burrow to her youngsters and moved into a vacant

burrow nearby at emergence time (Table 6).

Table 11 summarizes litter emergence data for

the two fall seasons, supplemented by data from two

litters that I observed emerging in spring 1975. During the fall of 1973, all three mothers transported

their litters to an alternate burrow prior to emergence. I never directly observed transport in process. Rather, I established the connection between

the mothers and the litter burrows when I observed

the mothers transporting nesting material (crushed

leaves) into the alternate burrow during the 2 to 3

days prior to their litter's emergence (Figure 31).

After emergence, I observed no direct signs of

mother-young association and the mothers concentrated activities to the area around their respective

home burrows.

The distances at which the mothers deposited

their litters was variable, averaging 18 m (Table 11).

Female 22's 1973 litter emerged from a separate

burrow system very close (5.5 m) to their mother's

home burrow. On the other hand, $ 15 transported

her 1973 litter to the periphery of her range (34.1 m

from her burrow), well out of her central high use

area to a point within 7.5 m of the home burrow of

another lactating female. Female 10 transported her

litter 24.6 m from her burrow, placing them equidistant from her and a neighboring female's burrow.

During the fall of 1974, three or four litters ( $ 15,

$30, $44, $45, Table 11) emerged from their

mother's home burrow and shared the burrow with

their mother. However, both members of $ 30's

litter were utilizing a burrow 9.1 m from their

mother's burrow only two days after emergence.

Female 22's litter emerged from her home burrow,

but she moved at emergence time to a vacant bur-
22

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 11.—Litter emergence data for mothers on the study plot (question mark indicates that

the identity of the mother was not certain)

Mother

Fall 1973

9 10

9 15

9 22

Fall 1971*

9 15

9 22

9 30

9 Uk

9 ^5

9 U8'

9 50?....

9 53?....

Spring 1975

9 22

9 70

Distance litter emerged

from mother's home burrow

m (ft)

2U.6 ( 81)

3U.1 (112)

5.5 ( 18)

From home "burrow

From home burrow

From home burrow

From home burrow

From home burrow

9.1 ( 30)

22.9 ( 75)

12.2 ( 1*0)

From home burrow

From home burrow

Comments

At emergence 9 22 moved to

a vacant burrow 18.9 m away.

Litter was observed utilizing

a different burrow 9.1 m

away 2 days after emergence.

Then 9 22 plugged entrance with

leaves and began using a new

entrance to same burrow system around

3.7 m away. Her litter was not seen

again in the vicinity of her burrow.

row 18.9 m away and utilized it as a permanent

burrow site thereafter. Three females ($48, 9 50,

9 53) transported their litters. All three were in

lactating condition in early September, but no

juveniles emerged from their home burrows. I did,

however, observe litters to emerge on their home

ranges from previously uninhabited burrow systems.

Further, I saw each of the females utilizing the areas

near the litter burrows around emergence time. I

did not see any direct sign of association between

the mothers and the litters.

During spring 1975, I observed two litters, both

emerging from their mother's home burrow. However, $ 22 plugged her nest hole entrance two days

after emergence and began using a new entrance.

I never saw her litter in the area around her burrow thereafter. Perhaps her litter and the 1974

litter of 930 were moved to an alternate burrow

just after their emergence from the home burrow.

Female 22 did not share burrows with her emerging litter during fall 1973 or fall 1974 (Table 11).

This matter of intolerance of mothers toward their

emerging litters is discussed further in the section

on social behavior.

My observations concerning litter transport prior

to emergence (or just after emergence) are relevant

to other studies of the eastern chipmunk. In the

dispersal study by Roberts and Snyder (1973), the

mothers of newly captured juveniles were determined mainly by the burrow location of the nearest

lactating female. My results indicate that one must

be careful in assuming that juveniles emerge at a

location nearer to their mother's burrow than to

the home burrows of neighboring adult females.

To my knowledge, my study is the first to indicate

that litters may emerge at sites other than their

mother's home burrow.

JUVENILE DISPERSAL AND HOME RANGE FORMATION

I have indicated that the utilization of the litter

burrow by littermates after emergence is short-
NUMBER 265 23

lived, with dispersal from the burrow occuring

within two weeks after emergence. Almost immediate dispersal of chipmunk young after emergence

was also noted by Roberts and Snyder (1973). They

often captured juveniles for the first time at considerable distances from their supposed birth sites

and they evoked quick dispersal as an explanation.

None of the juveniles listed in Table 10 adopted

the litter burrow as a permanent homesite, with

the exception of juvenile $70 during the fall of

1974, who remained in her mother's previous home

burrow after the other members of the litter dispersed. These observations lead me to conjecture

that most alternate litter burrows are not suitable

for permanent habitation, and litter members must

search the habitat for vacant and suitable burrow

systems. In the cases listed (Table 11) where

mothers shared their home burrows with their

emerging young, the youngsters dispersed and the

mothers remained in the home burrows.

The calculation of actual average dispersal distance for litter members is difficult because individuals dispersing off the study plot are not censused and cannot be distinguished from cases of

mortality. Further, juveniles suddenly appearing

on the study plot are not necessarily immigrants;

they may be young of resident adult females that

managed to disperse before being captured and

marked.

Table 12 summarizes dispersal distances of all

marked juveniles of known parents that remained

utilizing the study plot through the fall season.

Distances are from the mother's home burrow

(which is not necessarily the litter emergence burrow) to the juvenile's newly acquired burrow or

to the juvenile's geometric home range center. In

cases where burrows were not located until the

following spring, or when juveniles shifted their

ranges from fall to spring, I used the spring burrow

or home range center in the calculation.

TABLE 12.—Juvenile dispersal distances (note that male juveniles tended to disperse over

greater distances than female juveniles; difference significant at p = 0.01, Kruskall-Wallis

one way analysis of variance; Siegel, 1956)

Juvenile

Fall 1973

d 26

9 32

d 37

9 ^5

Fall 197U

d 2

d 8

o* 12

9 25

9 36

9 56

9 66

9 70

d 71

Average for

population

Average for

males....

Average for

females..

Mother

15

22

10

10

53?

30

30

15

22

22

22

22

30

Interburrow

m

29.9

21.3

38.1

M.I

73-2

53.3

39.6

7.6

2k.k

38.1

22.9

18.9

36.6

3^.2

U5.1

2U.9

distance

(ft) Comments

( 98)

( 70)

(ca 125) To spring I97U high use area;

burrow location unknown.

(135) To spring 1971* burrow.

(2U0)

(175)

(130)

( 25)

( 80) To fall 197^ high use area;

burrow unknown.

(125)

( 75)

( 62) Stayed in litter burrow.

(120)

+ 16.7 (112 + 55)

+ 15.7 (lk8 + 52)

+ 11.5 ( 82 + 38)
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Several points are apparent from the data in

Table 12. First, most of the marked juveniles established home burrows within 40 m of their mother's

home burrow, such that their movement patterns

subsequently overlapped with their mother's and

some sharing of space occurred (see Figures 13 and

14). Five female juveniles (9 25, ? 32, 9 36, 9 66,

9 70) adopted burrows quite close to their mother's

home burrow. This data reveals that many juveniles

(especially females) establish ranges neighboring

their mother and in many cases neighboring one

another. I do not attempt to relate juvenile dispersal distances to the burrow location of fathers

because of difficulty in determining the identity

of fathers (see "Mating Behavior").

Male juveniles showed a significant tendency to

disperse to greater distances than female juveniles

with Jc?8 (53.3 m) and Jtf2 (73.2 m) setting up

ranges that did not overlap with their mother's

ranges. Juvenile cf2 had the longest recorded dispersal distance.

Dispersal distances calculated by Roberts and

Snyder (1973) are comparable to my own measurements. Most distances were within 40 m of the

mother's home range center. The longest dispersal

distance they recorded was 95 m. Roberts and

Snyder did not mention a tendency for male juveniles to disperse over greater distances than female

juveniles. Their data contribute to my own in confirming the notion that close genetic relationships

exist between neighbors in chipmunk populations.

During the dispersal stage, a primary activity of

juveniles is to locate vacant burrow systems suitable

for permanent habitation. I observed no cases of

dispersing juveniles (or adults) excavating complete burrow systems on my study area. Evidently,

chipmunks move into vacant, pre-established systems, and perform only small excavations to keep

their burrows in order. Burrows are probably located during food gathering and exploratory treks

by juveniles when they are still residing in their

litter burrows. Some juveniles may temporarily reside in inadequate burrow systems after dispersal,

awaiting the location of a more suitable site at a

later date.

Table 13 presents the minimum home range

sizes of juveniles, calculated from the fall 1973 and

fall 1974 VC maps in Figures 13 and 14. These

figures may be compared with the areas calculated

for adults in Table 9. Comparisons must be reTABLE 13.—Juvenile minimum home range areas

during the fall period (measured directly from the

VC home range maps in Figures 13 and 14; compare with the adult home range areas for the same

time period—see Table 9)

Juvenile

Fall 1973

J 9 25

J a 26

J 9 30

J 9 32

J cr 37

J 9 *+5

Average

Fall 197*+

J cT 2

J cr 8

J d- 12

J cr 20

J 9 25

J 9 1+0

J 9 56

J 9 70

J cr 71

Average

Home range

acre

0.22

0.1+6

0.1+2

0.36

0.1+0

0.60

0.1+1 + 0.121+

0.36

0.29

o.37

0.16

0.30

0.31

0.1+0

0.16

0.26

0.29 + 0.09

area

hectare

0.089

0.186

0.170

O.1U6

0.162

O.2U3

0.166 + 0.050

0.11+6

0.117

0.150

O.O65

0.121

0.126

0.162

O.O65

0.105

0.117 + 0.035

stricted, however, to between the two age groups

(adults vs. juveniles) within each season. Comparisons between seasons are complicated by differing

study plot sizes, slightly different portable-stand

rotation schemes, and a differing number of observation periods between the two years. All three of

these factors affect home range area estimates.

Although juveniles exhibited smaller average

home range size than adults during both seasons,

the differences were not significant (Kruskall-Wallis

one way analysis of variance; Siegel, 1956). This

leads to the conclusion that fall emerging juveniles

establish and utilize home ranges approaching

adult size.

Some juveniles exhibited shifting home range

location through the fall period, or from fall to

spring. Juvenile 9 45 had a large (0.6 acre or 0.24

ha) home range during the fall of 1973 (Figure 13).

I divided her VC home range data into an early

fall and a late fall period to check for shifting. A

shift in activity to the north through the fall season was apparent, with a difference of 9.6 m between geometric home range centers. I did not lo-
NUMBER 265 25

cate J 9 45's burrow during the fall of 1973. In

spring 1974, I found her utilizing a burrow to the

north of the study area (Figure 6) and her home

range center for the spring period had shifted another 27.5 m north, to a point slightly off the study

area. It is my feeling that J 9 45's range was shifting

through the fall period as she searched for a vacant

burrow system. She probably established herself in

the permanent burrow shortly after I terminated

observations in late October of 1973.

Juvenile c? 37 also demonstrated a shift in home

range location from fall 1973 to spring 1974 (Figures 6 and 13), moving his activity center to the

west and off the grid (approximately 15 m change).

During the fall of 1974, J 9 36 shifted her home

range suddenly. She utilized a specific area in the

central portion of the grid (Figure 14) until midOctober. Then she suddenly shifted her activities

to an area just off one corner of the grid (marked

by X's in Figure 14), approximately 23 m from

her former activity center. After three days, she

returned to her original home range and remained

there for the duration of the fall period of observation.

SUMMARY

Analysis of adult home range use-patterns during

the fall nonbreeding period support the conclusions generated in the analysis of the spring nonbreeding data. These data add to the validity of

Figure 12 as a summary diagram of the primary

aspects of spacing in the nonbreeding population.

The data on spacing included herein serve as a

basis for the analysis of social behavior and foraging ecology during the autumn period. The major

points derived from my analysis of juvenile emergence and dispersal during September are as follows.

1. Considerable synchrony in emergence of

young occurs, with most juveniles emerging over a

two week interval in September. This probably reflects synchrony in summer estrus in the population

(see "Mating Behavior"). Estimated age upon

emergence from the natal burrow is 44 days.

2. Variation in the location of emergent litters

with respect to their mother's home burrow occurs,

with the following major patterns evident: (a) the

mother and litter share the mother's home burrow

at emergence time; (b) the mother transports her

litter to an alternate vacant burrow within her

home range confines at emergence time, and returns to her home burrow, having little to do with

her litter thereafter (these transported litters may

then emerge at a location nearer to the home burrows of other adult females than to their mother's);

or (c) the mother may give up her home burrow

to her litter at emergence time and move permanently into an alternate burrow system in her home

range.

3. Juveniles disperse from their natal burrows

within two weeks after emergence (late Septemberearly October), locate and adopt vacant burrow systems in the habitat, and establish ranges during the

month of October. Home range use-areas of juveniles during October approach that of adults.

Some juveniles shift their home range location

through the fall period or from fall to spring, a

phenomenon probably related to the search for an

adequate burrow system.

4. Juvenile dispersal distances vary greatly (7.6-

73.2 m), but young commonly set up home ranges

next to, and overlapping with, one another and/or

their mother. This trend points to the existence of

close genetic relationships between neighbors within

the chipmunk population.

Social Behavior in the Chipmunk Population

Adults and Postdispersal Juveniles

With the exception of anecdotal observations

in several early studies that indicated sociability

and gregariousness in the eastern chipmunk (Kennicott, 1857; Seton, 1929: 195; Allen, 1938: 86-88),

most investigators have agreed that individuals of

both sexes are solitary, aggressive, and intolerant,

and that no long term social bonding occurs (Burt,

1940: 44; Blair, 1942; Manville, 1949: 52; Dunford, 1970: 228; Neidhardt, 1974; Ickes, 1974). My

spatial studies, and those of the forementioned investigators, have shown that home ranges of individuals overlap to a considerable extent, such that

individuals do not occupy exclusive areas in space.

This lack of discrete, non-overlapping home areas
26

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

in the socially intolerant chipmunk raises an interesting question concerning aggression in the

species: If two individuals aggressively encounter

one another and both are well within the confines

of their own home ranges, then what are the determinants of dominance in the interaction?

Wolfe (1966) investigated aggressive behavior in

the eastern chipmunk and demonstrated a potential

for the development of stabilized dominance relationships between individuals. Unfortunately, his

investigations were carried out under artificial laboratory conditions, where many individuals were

confined to a small space. Dunford (1970) analyzed

social interactions in a natural population in New

York, and arrived at interesting conclusions concerning social dominance in the field that contrast

with Wolfe's conclusions. By placing artificial food

sources at varying distances from the burrows of

marked indivduals, Dunford demonstrated dominance in social encounters to be a function of

proximity to the home burrow. Individuals tended

to be dominant in encounters near their burrow.

Ickes (1974) generated further support of these

notions by conducting field experiments using artificial food sources and by running caged encounters

in the laboratory.

My study was undertaken to test the validity of

Dunford's conclusions and to expand upon them

through the observation of naturally occurring social interactions in a field population. This section will be restricted to a consideration of data

gathered during nonbreeding periods, so that social

interactions are not heavily complicated by the

existence of sexual motivations (see "Mating Behavior").

Juveniles emerged from their natal burrow in early

fall on the study area (see "Juvenile Emergence").

Therefore, an analysis of social interactions in the

fall is complicated by the existence of a juvenile

cohort in the population.

I gathered social interaction data during the spring

and early summer of 1974 (May-June), and during

the fall of 1973 and 1974 (September-October) on

the Adirondack study plot. I monitored encounters

between individuals while I was involved in gathering data on spatial use (see "Spatial Use") or

during trapping activities and casual walks across

the study area. Whenever I observed an encounter,

I attempted to record the identity of the participants, the location of the encounter, and the outcome. The most useful data are derived from

encounters where the participants and their home

burrow locations were known. I observed many

additional encounters involving unmarked animals living just off the study plot, or animals with

unknown burrow locations. All encounters were

naturally occurring and were not stimulated by

artificial manipulations of food resources.

SOCIAL INTERACTIONS AMONG ADULTS

During the nonbreeding season, the commonest

form of social interaction is the aggressive chase

(Figures 17, 18). Generally speaking, if a resident

becomes aware, either by visual or by auditory cues,

of an intruder in the central portion of his home

FIGURE 17.—Aggressive chase. The resident individual (left) chases an intruder from a

concentrated food source.
NUMBER 265

27

a

FIGURE 18.—Aggressive chases: a, b, open-mouth attacks; c biting of the flank during a chase.

(Drawings made from still photographs.)

range, he quickly approaches and proceeds to chase

the intruder out of the central area. Most aggressive chases occur over short distances (3^1.5 m), but

longer chases up to around 15 m take place on

occasion. Normally, no physical contact occurs during chases, the intruder running away as soon as

he perceives the approaching resident. If the resident closes in on the intruder during a chase, he

may attack with his mouth open and incisors bared,

in an apparent attempt to bite his retreating adversary (Figure 18a, b). Biting is rare, but does

occur on occasion (Figure 18c). Sometimes, the

resident approaches and snaps aggressively at the

intruder who quickly retreats (Figures 19, 20). The

resident then resumes foraging without expending FICURE 19_Aggressive snapping (drawn

energy on an extended chase. graph).

from still photo-
28

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 20.—Aggressive snapping. Note that the eyes of the aggressor are closed.

The pursued individual may employ methods

other than a quick retreat to his home area to

lose the aggressor. He may stop suddenly and remain completely motionless (freezing), thereby

making it difficult to be visually located. He may

also employ the strategy of reversing suddenly and

fleeing in the opposite direction. Often, a quick

reversal of motion is followed by freezing. If the

intruder is cornered, he may suddenly catapult

wildly into the air, performing an aerial somersault

to avoid contact with the approaching resident

(Figure 21).

Momentum may accompany a chase, allowing

the resident to chase the intruder well into the intruder's own central area of dominance. Usually, the

pursued individual turns on the aggressor at this

point and chases him back into his own central

area. Such reversals of dominance during ongoing

chases are very helpful in demonstrating the dependence of dominance on spatial location. Sometimes several reversals occur in the area intermediate between the participant's home range centers,

followed by both individuals sniffing about (mock

foraging) within several feet of one another before

retreating in the direction of their respective home

range centers. This type of standoff situation indicates equilibrated dominance relationships at that

location and may be used to define a boundary

zone. Tolerance in the absence of any chasing is

also indicative of a balance in dominance at a particular location; two neighbors may pass close to

one another during normal exploratory and foraging activities and seemingly ignore each other in

the boundary zone.

Fighting is rare, but may occur when two individuals attempt to chase one another in the zone

of balanced dominance. The two opponents jump

at one another, trying to bite or scratch with their

forepaws. Then they lock together and roll about

on the ground in a ball. Such roll-tumble fights

(Figure 22) usually end with an aggressive chase by

the victor, or with the two opponents facing one
NUMBER 265 29

FIGURE 21.—Leaping to avoid being bitten: a,

subordinate individual prepares to leap; b, subordinate individual somersaults into the air.

(Drawn from still photographs.)

another in standoff before retreating. Fights may

occur near home range centers if the resident corners an intruder so that he cannot retreat.

I never observed noticeable physical damage as

a result of aggressive social encounters. Since individuals do attempt to bite opponents with their

incisors, however, wounding may occur periodically.

A photographic analysis of roll-tumble fights (Figure 22) and snapping at close range (Figures 19,

20) revealed that the participants often keep their

eyes closed during contact. It is probable that this

behavior functions to protect the eyes from serious

damage as a result of biting and/or scratching.

SPATIAL DYNAMICS AND ANALYSIS OF SOCIAL

BEHAVIOR

In Dunford's (1970) analysis of social interactions, home range size was treated as a linear dimension since chipmunk burrows fell along a

hedgerow only 5-6 meters wide. This kind of representation neglects the two dimensional nature of

chipmunk home ranges in other habitats, as well

as variation in use-intensity over different portions

of the home range. Thus, correlation between dominance and actual spatial use-patterns, other than

proximity to burrow, cannot be made. Further-
30

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 22— Roll-tumble fighting (drawn from still photographs).

more, by providing artificial food sources, normal

movement patterns of individuals may be drastically influenced.

My studies of spatial use-patterns in the Adirondack population have taken into account both the

two dimensional nature of the home range, as well

as variations in use-intensity patterns over the home

range. Figure 12 summarizes spatial dynamics, depicting the approximate spatial use relationships

between neighboring adults in the nonbreeding

Adirondack chipmunk population. The conclusions

of the spacing study allow spatial dynamics to be

viewed as reasonably formalized in structure. This

greatly simplifies the analysis of social interaction

data. Burrows are nearly always located in the highuse central area very close to the geometric center

of the home range. The burrow position can thus

be equated with the home range center. Furthermore, since activity (time spent per unit area) decreases with distance from the home range center,

it is reasonable to assume that the individuals

familiarity with his surroundings also decreases

with distance from the burrow.

ADULT-ADULT SOCIAL INTERACTIONS

I observed a total of 102 adult-adult aggressive

chases during the nonbreeding season where both

participants were identified and the locations and

outcomes of the chases recorded. Eighty-three of

these chases were between close neighbors and usually occurred in the area between their home burrows. The other 17 occurred when individual chipmunks made long excursions into the home areas

of distant individuals. In all 17 cases where chipmunks interacted with residents during long excursions, they were treated and responded as of

subordinant status and were chased out of the

resident's home area. For a quantitative consideration of aggressive chases occurring during the nonbreeding period, I restrict myself to an analysis of

the 83 encounters between neighbors so that the

data are not skewed by encounters resulting from

long distance excursions. A total of 19 individuals

(6 males and 13 females) in various pair combinations gave rise to the 83 chases. The greatest number

of chases attributed to a specific pair was 15; most

pairs contributing only several chases to the data

pool. The predominance of females in the encounter data stems largely from the fact that several
NUMBER 265 31

females inhabited the central portion of the study

grid, while most males under study had burrows

near the periphery or off the study area (see "Spatial Use").

I define the point of initiation of a chase as the

position of the subordinate individual (the one who

gets chased) when the chase begins. An individual's

readiness to attack in an encounter situation is

dependent on the location of the other individual,

rather than his own location. Residents foraging

on the periphery of their ranges, where they are

normally subordinate in encounters, upon becoming aware of an intruder in their own central area

would charge the intruder without hesitation. A

measure (X) is calculated for each of the 83 chases

that compares the distance from the dominant's

burrow to the initiation point (D) with the distance

from the subordinate's burrow to the initiation

point (S).

TOTAL

<Q5

61

X =

D

D+S

If the value of X falls below 0.5 for a single encounter, it indicates that the chase initiation point

is farther from the subordinate's burrow than from

the dominant individual's burrow. If dominance is

dependent upon proximity to the home burrow or

home range center, most X values are expected

to fall below 0.5, indicating the subordinate individual was trespassing into the dominant's core

area.

Figure 23 presents a histogram of the distribution

of X values for the 83 chases between adult neighbors; 73% (61 of 83) of the values fall below 0.5,

supporting the space-dependent notion of dominance (significant at a — 0.001, x

2

 one-sample test,

Siegel, 1956). Another point may be derived from

this histogram that must be kept in mind when

analyzing naturally occurring encounters. If the

histogram is folded over at the midpoint value, a

curve is produced indicating where social encounters between neighbors are most likely to occur. The

curve demonstrates that most chases between neighbors occur in the zone intermediate between their

burrows, with few encounters occurring in close

proximity to home burrows.

Figure 24 presents a histogram representation

of the actual distances from home burrows of the

dominant and the subordinate individuals at which

TOTAL 22

in

in

<

x

o

o

30-1

20-

10-

2

ri

g

7

01

A

7

3

•

A

16

s

8

A

29

8

o

A

14

cS

8

A

50.6

A

o

A

2

§0.8

A

0

Q

§

A

X VALUE CLASSES

FIGURE 23.—Histogram of X values derived from 83 chases

between adult neighbors.

the 83 chases were initiated. The hypothesis that

dominance depends upon proximity to the home

burrow leads to the prediction that the average

distances from the burrows of dominant individuals

will be less than the average distances from the burrows of subordinate individuals. The data in Figure 24 bear out this prediction, with the average

distance from the burrow for dominant individuals

being 13.4 ± 7.0 m (44 ± 23 ft) and the average

for subordinate individuals being 18.3 ± 7.9 m

(60 ± 26 ft).

The histograms in Figure 24 also allow for the

estimation of an average distance from the burrow

where the probability of dominating in an encounter equals the probability of being subordinate. By comparing the frequency scores for subordination and domination (the fractions in Figure

24) in progressively increasing distance classes, it is

demonstrated that domination is more probable

up to and including the 9-12 m distance class,

while in the next distance class (12-15 m), subordination predominates. Furthermore, except for two
32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

dominant individuals

subordinate individuals

Distance from Burrow (m)

FIGURE 24.—Histogram representations of the distance from the home burrow of dominant and

subordinate adults derived from 83 chases between neighbors. The fractions compare the ordinate

value for dominant individuals (numerator) with the ordinate value for subordinate individuals

(denominator) in each distance class.

minor deviations, subordination predominates in

all distance classes greater than 12 m. This offers

further support for the space-dependent hypothesis

where a dominance switch is expected as distance

from the home burrow increases.

The conclusion that can be drawn from Figures

23 and 24 is that, on the average, an individual is

likely to be dominant in encounters with neighbors

occurring within around 12 in of his burrow, while

he is likely to be subordinate at greater distances.

Correspondence with spatial use data is apparent

when the summary diagram of spatial relationships

between neighbors during the nonbreeding season

(Figure 12) is compared to these conclusions. The

average interburrow distance for the adult population was calculated at around 24.4 m placing the

average intermediate zone between neighbors at

approximately 12.2 m.

Further support of the space-dependent hypothesis comes from an analysis of qualitative aspects of the 83 chases. Almost without exception,

the individual initiating a chase chased the subordinate away from his (the dominant's) burrow, and

the subordinate retreated in the direction of his own

burrow. Analysis of cases of tolerance between

neighbors, and fights and chases that resulted in

standoffs, is also supportive. I recorded 13 cases,

12 of the 13 occurring in areas intermediate between the neighbor's burrow locations, precisely

where interactions of this nature would be expected

to occur.

Another observation that supports the spacedependent viewpoint is the occurrence of reversals

of dominance during on-going chases. I observed a

total of 13 encounters between known adults that

included reversals. All 13 occurred between neighbors in areas intermediate between their home burrows. Furthermore, the dominant individual always

chased the subordinate away from his home range

center and towards the subordinate's center. The

subordinate, upon approaching his own center,

turned and chased his opponent back toward his

opponent's center. I noted as many as three reversals during single encounters, and the directions

and locations of the reversals always corresponded

to this pattern. Several reversals resulted in standoff
NUMBER 265 33

with toleration in the intermediate zone, followed

by both individuals retreating towards their home

burrows from the hypothetical boundary.

Thus far I have not considered interactions between single pairs. I did not gather enough data to

perform detailed analyses, but I will present data

for two pairs that are informative. Figure 25 illustrates chases, fights, and cases of tolerance that I

noted between the neighbors $ 15 and $30 during

the spring of 1974. Any reversals are depicted as

simple chases in the diagram. Note that $ 15 and

$ 30 usually encountered one another about midway between their burrows. Both individuals initiated chases in that area, indicating a balance of

dominance. The directions of the chases conform

to the space-dependent hypothesis, and all cases of

fights and tolerance fall in the boundary zone.

Figure 26 presents interactions between cf 18 and

$30 during the spring of 1974. Again, the directions and locations of the chases, and the locations

of cases of tolerance, indicate that a boundary

zone of equilibrated dominance exists. However, in

this example it appears that $30 dominates cf 18

into areas fairly close to his home burrow. In other

words, there appears to be an individual difference

$30's

Burrow

n

$15's

Burrow

T= Tolerance

F= Fights

«-O = Chases by $15

«-*= Chases by $30

<£L8's

Barrow

Vie*

/Qv

\T

X-

$30's

Burrow

o®

T = Tolerance

«-o= Chases by $30

«-X= Chases by d"18

|—?.63 m,H

(25 ft) '

FIGURE 25.—Aggressive interactions between $15 and $30

during the spring and fall of 1974 (arrows indicate direction

and distance of chases).

I— 7-63 m ~\

' (25 ft)

 n

FIGURE 26.—Aggressive interactions between £18 and $50

during the spring and fall of 1974 (arrows indicate direction

and distance of chases).

in aggressiveness that moves the point of balance

closer to <J 18*s home range center. I do not know

to what extent individual adults may vary in this

respect, but I do expect these types of imbalances

to be common in the population. Elements of the

Dunford hypothesis, however, still apply to this

example. In spite of individual differences causing

a boundary shift, space-dependent aspects of dominance are still obvious in the pattern of social interaction between the two neighbors.

I presume individual differences in aggressiveness

to be the major factor responsible for social interactions producing high X values (Figure 23). Pairs

with a boundary shifted in favor of one individual

may behave in a manner consistent with a spacedependent hypothesis and still produce X values

greater than 0.5. This complication is the major

drawback of lumping data from many pairs for

analysis.

CONCEPTS AND TERMINOLOGY

The information I have presented supports the

notion that dominance in aggressive encounters has

a "psychological" component that is space-depend-
34

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ent, with the tendency to attack being greatest near

the home burrow and decreasing with distance

from the burrow. Since burrows are centrally located in a relatively symmetrical home range, and

since time spent per unit area is greatest near the

home range center and gradually decreases toward

the periphery (Figure 12), then the tendency

to attack is also correlated with intensity of use

of the area in question and perhaps "familiarity" with the area. An individual is more likely

to initiate a chase on his "home turf." The

existence of this component adequately explains

the directional qualities, locations, and outcomes

of most encounters, as well as the existence of

boundary zones of equilibrated dominance.

The real world, however, is not so simple. Aggressive encounters often occur that are counter to

the generated predictions, these encounters indicating the existence of other factors affecting social

interactions. Apparently, individual differences in

psychological makeup and physical prowess (size

and strength) exist that affect the results of aggressive encounters. These differences may be viewed

as being independent of space, in that they remain

constant regardless of spatial locations of the individuals in question. Such differences must be superimposed upon space-dependent psychological elements in order to arrive at a full understanding of

the problem of dominance in aggressive interactions.

It is probable that the dominance hierarchies that

Wolfe (1966) observed in captive chipmunk populations resulted from space-independent, individual differences. By placing many individuals together in a small cage, Wolfe minimized the effect

of space-dependent psychological elements of dominance. All individuals were "equally unfamiliar"

or "equally familiar" with the caged-in area. A

hierarchy then emerged based upon space-independent elements of dominance such as fighting ability

correlated with size. In fact, Wolfe felt size to be

the critical factor influencing position in the hierarchy. Similar experiments by Ickes (1974) in neutral arenas confirmed this viewpoint. Learned relationships between specific individuals are usually

important in the formation of dominance hierarchies, especially if the hierarchies lead to a decrease in the exhibition of overt aggression and

result in a stabilization of dominance-subordinance

relationships.

In natural populations, space-dependent and

space-independent elements must be taken into account together. In the boundary zone of equilibrated psychological tendencies, two neighbors are

likely to participate in fights. These fights allow for

a matching of physical attributes, such as strength

and agility. If one individual is stronger or faster

than another, it is probable that the boundary zone

will shift toward his neighbor's home range center.

Learning, as a result of periodic fighting, might

lead to a stabilization of the boundary zone location

and a reduction in actual fighting between neighbors. Thus, an element of the Wolfe type of dominance hierarchy may be found in natural populations, but only as it concerns neighboring pairs

and the delineation of boundary zones between the

pairs. Very few natural situations arise where many

adult individuals periodically gather on neutral

grounds, thereby simulating Wolfe's experimental

conditions (see "Special Situations").

Evidently, if an individual is attacked at great

distances from his burrow, he will flee regardless

of his physical attributes. A unique example illustrates this point. A resident adult female caught an

individual in the middle of her home range that

was on a long excursion from 90 m away. The resident attacked and the intruder fled, but the intruder retreated into a hollow log. The resident

pursued her adversary into the log and managed

to corner him so that he could not escape. Forced

to fight, the intruder was victorious. However, as

soon as he had displaced the resident female, he

very quickly retreated from the range. Thus, the

resident's usual dominance at that location is likely

to be more dependent upon a psychological advantage than any physical advantage.

DIFFERENCES ASSOCIATED WITH AGE AND SEX

My discussion so far has treated all adult individuals within the nonbreeding population as behaving basically the same, with the exception that

individual differences affecting dominance were

implied to exist. Sexual differences in either the

psychological space-dependent components or spaceindependent components were not obvious during

my study but I did not gather enough data to

analyze this problem in detail. Both sexes behaved

similarly and, although the boundary zones between adult males and adult females were often
NUMBER 265

35

skewed in favor of one sex (Figure 26), no definite

trend was discernible. Ickes (1974:43) felt that

males tended to dominate females during nonbreeding season, but the sex effect was minor when compared to space-dependent psychological effect related to distance from home burrows. The species

is not sexually dimorphic to any great degree. Both

sexes look alike at a distance and weights of adults

during the nonbreeding season are comparable,

although males are slightly heavier on the average

(Table 14).

TABLE 14.—Adult weights during nonbreeding periods (pregnant females not included) and juvenile

weights at emergence time

Individual

Adult males

Adult females

Adult males

Adult females

Juvenile males

Juvenile females

Weight

(gm)

Sep 1973 and

85.6

82.2

May 1974 and

79-7

75.0

Sep 1973 and

48.3

U7.6

S.D.

1974

6.74

5.44

1975

9.12

8.78

1974

5.77

1.03

N

11

16

26

37

19

20

Another possible source of imbalance in dominance relations between adults may be due to age

differences. I do not have data to analyze this problem because most of the adults in my population

were of unknown age. Ickes (1974) offered evidence

that old adults tend to dominate younger adults.

ADULT-JUVENILE SOCIAL INTERACTIONS

I gathered abundant data on interactions involving newly dispersed juveniles (1.5-3.0 months old)

during the fall of 1974. Although cohesive interactions between littermates, or between the mother

and her litter, may occur at emergence time (see

"Predispersal Social Behavior"), interactions involving post-dispersal juveniles are aggressive and conform to the general descriptions I have already

given for adults.

Analysis of social encounters between adults and

juveniles indicate that adults are usually dominant

over juveniles, regardless of the spatial location of

encounters. This trend would be expected if dominance is related to size since newly emerged juveniles

weigh only GO percent as much as adults during

the fall period (Table 14). During SeptemberOctober 1974, I observed a total of 79 chases between marked adults and marked juveniles. In 67

of these chases (85%), the adult dominated. Of the

chases 45 involved juveniles whose burrow locations were known, allowing me to calculate X

values (p. 31) and to test if the chases conformed

to a typical space-dependent scheme.

Table 15 shows a breakdown of the 45 chases. In

36 of the 45, the adult dominated. However, in 22

of those 36 dominations, the juvenile was closer

to his home burrow than the adult (X values were

greater than 0.5). This is contradictory to the spacedependent hypothesis, and indicates that adults

commonly dominate juveniles in social encounters

occurring close to the juvenile's home burrows.

In 9 of the 45 chases, juveniles dominated. In 8

of those 9, the juvenile was closer to his home burrow (X greater than 0.5). This indicates that juveniles may dominate adults on some occasions,

but the juveniles are usually close to their burrows

when they do it. In only one case did a juvenile

dominate an adult in the adult's home area. The

adult, however, after being chased for a short distance, turned on the juvenile and quickly chased

him completely from the area. I observed five instances where juveniles tolerated adults at close

range. In all five, the adult was in areas close to

the juvenile home burrows.

TABLE 15.—Results of 45 adult-juvenile chases where burrow

locations were known (X values have been previously defined

—see Figure 23 and accompanying text)

Chase results

Adult wins

Total

Juvenile wins

Total

X values

-=0.5

>0.5

-=0.5

>0.5

No. of chases

14*

22**

36

8*

9

•Expected under space-dependent hypothesis.

**Unexpected under space-dependent hypothesis.
36

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

I gathered similar data during the fall of 1973. I

recorded 25 adult-juvenile encounters and the

adults dominated in 21 of these (84%). The four

cases of juvenile domination all took place close

to the juvenile home burrows.

As inferred from Figure 23, a percentage (27%)

of adult-adult encounters have X values greater

than 0.5. These probably come from chases between neighbors where the boundary zone of equilibrated dominance is shifted in favor of one individual. I showed earlier that space-dependent elements of dominance may exist in spite of individual

differences in psychological makeup or physical

prowess (Figure 26). Thus, the existence of chases

with X values greater than 0.5 may not preclude a

space-dependent scheme.

During interactions between adults and juveniles,

elements of adult aggressive behavior occur. I observed repeated examples of reversals during ongoing chases, tolerance of individuals at close range,

and fights resulting in chases or standoff situations.

In addition, the directional components of these

behaviors corresponded to that described for adults

(see "Adult-Adult Interactions"). These observations support a space-dependent scheme of dominance. At the same time, my conclusions regarding

the spatial locations of chases and the other behaviors support the notion that the hypothetical

boundary zone of equilibrated dominance is shifted

drastically in favor of adults. Below I shall give

specific examples illustrating that space-dependent

elements of dominance occur in spite of the apparent physical advantage that adults have over juveniles.

During late September 1974, J $70 settled in her

natal burrow, her mother (A 9 22) moving into a

burrow around 18.9 m away at emergence time (see

"Juvenile Emergence" and Figure 14). During October, I observed 11 chases between these two individuals. A 9 22 dominated in 10 of the chases and

in 8 out of the 10 was closer to J97O'S burrow

than to her own. These data indicate almost complete domination of J 9 70 by her mother, even in

areas close to J 9 70's burrow. Only once did I

observe J 9 70 attack her mother, and that attack

occurred within 3 m of the juvenile's burrow entrance. Thus, the juvenile exhibited typical attack

behavior, but only in close proximity to it's burrow.

Juvenile 970 acted differently towards intruding

juveniles. I recorded two instances where she chased

juveniles from an area 9 m from her home burrow.

In the same area she was subordinate to A 9 22.

This introduces the possibility of age class (or individual) recognition resulting in differential responses toward different intruders.

A similar description revolves around J $ 8. Juvenile cf8 moved into a burrow around 18 m from

A950's burrow (Figure 14). During October of

1974, I observed 10 chases between these two individuals. Adult 950 dominated in 7 of these, with

5 of the 7 occurring closer to Jc?8's burrow than

her own (3 of the 5 took place within 3 m of J c? 8's

burrow entrance). Juvenile (^8 dominated A 9 50

three times, with two of those dominations occurring close to his home burrow. A single chase occurred where J $ 8 attacked A 9 50 near her burrow,

but A 9 50 quickly retaliated by halting her retreat

and chasing him away.

Juvenile tf 8 also produced evidence for age class

(or individual) recognition. During October, I

watched him dominate in chases with three different intruding juveniles at distances of 12-13 m from

his burrow. Yet, I observed him to tolerate A 9 50's

presence within 3 m of his burrow on three occasions during the same time period.

Two additional examples offer evidence for age

class or individual recognition. Juvenile 9 25 chased

J 9 33 without any hesitation from an area 18 m

from her home burrow. Seconds later, A cf 18 passed

in front of her at the identical location and J 9 25

sat motionless, staring in his direction, until he

left the area. On another occasion, Jcf2 chased

J 9 36 out of an area nearly 30 m from his burrow.

Within a minute, A 9 22 wandered through the

same area and Jcf 2 watched her go by without

charging. If individual recognition occurs in the

population, then learned hierarchial relationships

may exist, but only between neighboring pairs as

it relates to the delineation of the boundary zone

of equilibrated dominance between the pair.

SPECIAL SITUATIONS OF SOCIAL INTERACTION

During late June of 1974, a concentrated food

source appeared 30 m beyond one corner of the

study plot. A single red maple tree had produced

a large seed crop, while all other red maples in

the vicinity had seed crop failures. Many of the

residents on the study plot located this food source

and began making periodic long excursions to the
NUMBER 265 37

tree (p. 78 and Figure 47). Most of these individuals

gathered seeds in their pouches and transported

them back to their home range centers. Since the

seeds were only available in a limited area (circular area of 12 m diameter), it was common for

several individuals to forage in close proximity of

one another. This unique situation of having a

diverse group of chipmunks foraging together under a single tree provides an interesting social situation that can be contrasted with modal social dynamics.

During the late June period, each individual

occupied his normal home range and defended his

home range center from intruders. No individuals

at the red maple site appeared sufficiently close to

their burrows to consider it part of their home

grounds; all chipmunks were unfamiliar with the

area. Hence, the red maple site was a natural simulation of a neutral encounter area.

I observed as many as seven individuals foraging

under the tree at one time, these chipmunks commonly passing within several feet of one another

without arousing any overt aggressive behavior.

When two individuals passed within 0.6 to 0.9 m

of one another, short chases sometimes occurred

resulting in the displacement of one of the chipmunks. Foraging would then resume, with the two

individuals remaining within 1-3 m of one another. This contrasts sharply with the situation

on normal home ranges, where resident individuals

do not tolerate the presence of an intruder in the

home range center and rarely tolerate one another

at close range.

I noted longer chases of the typical home range

defense type when individuals left the red maple

site and transported food back to their home centers. During these trips, they moved across occupied

home ranges and encountered residents who would

chase them away without delay. The chases sometimes occurred between individuals who, only minutes before, had tolerated one another at close

range under the red maple tree.

Apparently, chipmunks foraging in such neutral

areas only attempt to maintain a short individual

distance of around 0.5-1.0 m. The outcome of small

displacement chases is probably dependent upon

space-independent elements of dominance such as

size. Therefore, a dominance hierarchy could potentially form that would be somewhat comparable to

those experimentally induced by Wolfe (1966). I

did not gather data at the red maple site to test

for a hierarchy. Group composition under the tree

was variable and the resource was short-lived. The

chipmunks depleted the seed source in a week's

time and returned to their normal home range

confines.

I noted a similar situation during the fall of

1974. A beech tree began dropping ripe seeds a

week before other trees on the study area. Four

individuals exhibited toleration while foraging

within 3 m of one another under the tree, which

was located on the periphery of all their ranges,

around 30 m from their burrows. All four were

out of their core areas (Figure 12), and seemed to

lack the attack tendency associated with home

ground. As in the case of the red maple tree, individual distances of 0.5-1.0 m were maintained by

periodic short displacement chases. This grouping

was very temporary, occurring intermittently over

a three-day period.

SOCIAL COOPERATION IN THE POPULATION

Previous discussion of adult social behavior has

centered around aspects of aggressiveness of individuals within the population who are pitted

against one another in a competitive sense. Most of

these aggressive behaviors can be readily explained

by their obvious advantage to the individual during competition for resources such as food or space.

Cohesive social interactions may be observed between the mother and her litter for a short period

of time after emergence, but these can be hypothesized as contributing to the survivorship of the

young. Further cooperation may be observed between males and females during breeding activities,

but the advantage of this type of cooperation is

apparent.

I observed another case of possible cooperation

in the Adirondack chipmunk population where the

advantage to the individual initiating the behavior

was not obvious. I will describe and discuss the

case here, as it introduces a new dimension to social

behavior that must be considered when dealing

with chipmunk social dynamics.

A common vocalization of the eastern chipmunk

in the Adirondack region is a low frequency (1-3

kHz), repetitive "chucking" (Figure 27). Seton (1929:

206) describes this vocalization and likens it to

the sound of the hoofs of a walking horse on hard
38

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

pavement. In the Adirondacks, the "chucking" vocalization is discrete, and is easily separated from

the higher pitched, repetitive "chipping" vocalization, although intermediate forms do occur. Dunford (1970: 224-225) includes "chucking" as a

variation of chipping. Neidhardt (1974: 41) in

agreement with my own observations, feels that it

is a reasonably discrete vocalization type.

Individuals often join into "chucking" choruses.

Large choruses of 8 to 10 or more individuals are

common during the spring, early summer, and fall

in the Adirondacks. Both Seton (1929:208, 210)

and Neidhardt (1974:44) recognized the contagious

nature of the vocalization. Seton recalled that Indian boys would often induce chipmunks to chorus

by mimicking the note. Seton, however, erroneously guessed that the vocalization was somehow

linked with the "erotic impulse" (1929:215). Neidhardt (1974:44) felt more realistically that the

vocalization was given in response to general disturbances in the habitat. However, she did not

provide any detailed information concerning the

exact nature of these disturbances.

The "chucking" vocalization was the most common chipmunk vocalization heard in the Adirondack population. Usually, a single individual

would go to a perch and begin "chucking" for no

apparent reason. This often induced neighboring

individuals to mount perches and to begin vocaliz8

§ 4

U"

£

IL. 2

ing, thus producing a chorus that spread through

the forest. The intensity of the "chucking" appeared to be an important variable. Loud "chucking almost invariably had an immediate and obvious depressing effect on the movements of neighboring individuals. If the neighbors were not induced to join the chorus, they would at least sit

motionless and alert. Softer "chucking" noticeably

depressed movements of neighbors, but usually did

not evoke chorusing.

For most of my study, the "chucking" vocalization's function, as well as the predominant releasing stimulus, remained a mystery. Then I observed

that "chucking" normally occurred following the

nights of aerial predators across the study area. An

unfortunate problem was that bird predators could

easily fly over the study site without my spotting

them. Thus, the disturbance eliciting choruses

often went unnoticed by me.

During the fall of 1974 and the spring of 1975,

I noted 17 instances of the flight of aerial predators (6 goshawks, Accipiter gentilis; 1 coopers

hawk, Accipiter cooperii; and 10 Buteo spp.) over

the study site at heights varying from 3—15 m. In

addition, I recorded three instances of attack of

chipmunks by hawks, although none involved successful captures. Whenever I saw aerial predators

fly across the site, chipmunks began "chucking"

in the area that the predator first appeared. Gradu0.5 1 1.5

Time (sec)

FIGURE 27.—Sonogram of repetitive "chucking" vocalization at 1-2 kHz.
NUMBER 265 39

ally a chorus spread along his flight path, finally

including individuals in the direction that the predator disappeared from view. Chorusing usually

lasted from 5-10 minutes, after which time most

individuals quit "chucking," left their perches, and

began to move around.

Several cases occurred where I obtained a close

view of individual response to the sight of a flying

predator. Each individual looked in the direction

of the predator and immediately commenced

"chucking" loudly, at the same time climbing to a

perch. The individuals then sat alert and gazed in

the direction that the predator disappeared, sitting

motionless and vocalizing for the duration of the

"chucking" bout.

The advantage of the "chucking" vocalization to

the vocalizing individual is not readily apparent.

Perhaps it conveys to the predator that it has been

located, thus invoking the predator to leave the

area. However, it is equally feasible that the vocalization draws attention to the vocalizing chipmunk

and thus invites pursuit (Smythe, 1970). The advantageous effect it has on neighboring chipmunks,

however, is quite obvious. It alerts them to the

presence of an aerial predator and results in immobilization. An alerted, motionless chipmunk is

probably not easy for a predator to catch. These

considerations raise the question of why an individual alerts his neighbors to a predator, when he

aggressively competes with them on a daily basis.

Hamilton (1964) introduced a theoretical argument concerning the evolution of altruistic behaviors directed towards genetically related individuals.

Briefly, if the detriment accrued by the actor is

small and the behavior is sufficiently beneficial to

a genetically related recipient, then the altruistic

behavior may survive in the population. The more

closely related individuals are, the more likely it

becomes that altruistic behaviors may occur between

them. If the "chucking" vocalization is interpreted

as being altruistic, then it would only be feasible

if neighbors in the population are genetically close

relatives. In my description of dispersal of young

in the Adirondack population (see "Juvenile Dispersal and Home Range Formation"), and in the

study by Roberts and Snyder (1973), it was demonstrated that many young chipmunks set up home

ranges very close to the site of their birth. Youngsters often established ranges overlapping with each

other or with their mother. These data indicate a

high potential for close genetic relationships between neighbors, a major requirement of Hamilton's theory.

The "chucking" vocalization conforms to other

constraints imposed by Hamilton. The detriment

accrued by the vocalizing individual is probably

very low, as the individual has already been alerted

to the presence of a predator and is prepared for

attack. On the other hand, the advantage accrued

by the neighbors is great. Cooperative behaviors of

other sorts may not be expected to survive in the

population. For instance, if an individual tolerated

the intrusions of related neighbors into his home

range center (of obvious advantage to neighbors),

it would drastically affect his own survivorship and

fecundity through the loss of critical resources such

as food hoards.

HIDDEN POLARITIES IN THE POPULATION

During my entire field study, I never found signs

of extensive diggings that indicated an individual

had excavated a new, complete burrow system. The

only signs of digging were small piles of dirt at

burrow entrances, indicating that minor changes

in the burrow system were being made by the resident chipmunk. A common maneuver was for the

resident to plug the burrow entrance with leaves

and dirt and open a new entrance a short distance

away. I uncovered the burrows of several chipmunks living off the study plot to investigate chipmunk food-hoarding behavior (see "Dynamics of

Burrow-Hoarding"). These investigations revealed

that burrow systems in the Adirondacks are relatively complex affairs that would require a considerable time and energy expenditure to build (Figures

48-50).

These observations lead me to believe that burrow systems are relatively fixed commodities in the

habitat (a similar situation has been described by

Calhoun, 1962:41-51, for the Norway rat, Rattus

norvegicus). Dispersing individual's probably spend

a considerable portion of their time searching for

adequate living quarters and it is doubtful that

they establish and defend a core area until such

quarters are located. Burrow systems become vacant

in the habitat as individuals disappear due to factors such as disease and predation. Turnover in

the Adirondack population during my study revealed that burrow systems are used consecutively
40

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

by different individuals (Table 6). Numerous burrows are probably available in the habitat that

are not fit for long-term inhabitation. Dispersing

juveniles may use these systems for short periods

of time while searching for permanent quarters.

The burrow system is of tremendous importance

to the individual. In it he hoards his winter stores

of food. In addition, it offers protection from predation. In areas, such as the Adirondacks, where

there's much precipitation with alternating thaws

and freezing during the winter months, the burrow

system protects the chipmunk from drowning and/

or freezing during the hibernating season. On the

basis of these points I conjecture that it is more

critical for dispersing individuals to locate a proper

burrow than to acquire a home range containing

maximal levels of food resources. In any event,

seasonal and yearly fluctuations in food resource

availability (see "Foraging Behavior") would make

it exceedingly difficult to predict in advance which

sites will provide maximal levels of food resources

in the future.

Individuals within the population may be

thought of as competing for the best burrow systems. Several observations support this interpretation and reveal that neighbors are cognizant of one

another's burrow locations. One observation was

made during the spring of 1974 and involved three

neighboring females. Female 21 accidently died in

a trapping accident in early May (Table 6).

Within several days, her neighbor ($ 10) investigated the empty burrow. Within a week, $ 10

had moved into 9 21's burrow, thus vacating her

own burrow. The following week, a third neighbor ( $ 22) robbed $ 10's former borrow of beechnuts that $ 10 had apparently left behind when

she moved. This example indicates that chipmunks find and explore their neighbor's burrow

within a short time after the neighbor's disappearance. The fact that 9 10 moved into $ 21's burrow

indicates that she found the burrow system of $ 21

more suitable than her own. I noted no obvious

food resource differences between the home ranges

of any of the three females during the spring period. Of further interest is the fact that 9 22, when

she had a litter the following fall, left her young

in her home burrow and moved into the burrow

of 9 10 that had been vacant all summer (Table 6).

Another observation indicates that neighbors may

know the exact location of one another's burrows. An adult female (9 30) was involved in a

mating bout on 4 July 1974 (Table 16). While she

was occupied with the males, I noted a neighboring

female (9 48) pilfering stored beechnuts from her

burrow. At any other time it is doubtful that pilfering could occur without drawing the resident's

attention to the robber. This incident did demonstrate, however, that 9 48 was cognizant of 9 30's

home burrow location, and, given the right opportunity, rushed in to haul away the hoard.

Obviously, some home ranges are better than

others (possibly because of their burrow systems),

and the removal of individuals holding optimal

positions would be expected to result in compensatory movements of other individuals to fill these

areas. Since individuals adopt and defend suboptimal sites, these polarities remain hidden and can

only be deciphered if the observer is familiar with

the population, the habitat, and the available burrow systems, and if the population is observed long

enough to see natural compensatory movements

occur. A realistic view of social dynamics, then,

must not only consider readily observable phenomena, such as dominance in social encounters,

but must also deal with the fact that certain hierarchial relationships exist in the population,

with some individuals occupying more suitable locations than others. A correlation of the suitability

of home range location with aggressiveness has not

been demonstrated. Some measure of luck is probably involved as burrows may be parceled out on

a first come, first serve, basis. Once an individual,

regardless of his physical prowess, has established

residence over a particular area and burrow system,

it would probably be difficult for another individual, however strong and agile, to take over the

location. Even if the contender had the physical

advantage, site-dependent factors affecting dominance would work in favor of the resident.

SUMMARY

I have described herein social behavior in adults

and postdispersal juveniles during the nonbreeding

season. Chipmunks are highly intolerant of one

another, defending the central portions of their

home ranges by chasing intruders from the area.

Data point to the existence of space-dependent,

psychological elements affecting dominance, such

that an individual's likelihood of dominating in ag-
NUMBER 265 41

gressive social encounters is greatest near his home

burrow or home range center. Adults of both sexes

and all age classes beyond the dispersal stage show

these site-dependent attributes. Comparing interaction data with spatial use data reveals further

correlation between the ability to dominate, intensity of spatial use, and familiarity with surroundings.

Site-independent individual differences in physical attributes or psychological makeup are also inferred to exist in the population, and examples are

provided. These differences may be responsible for

the shifting of boundary zones of equilibrated dominance between neighbors. Further, they are postulated as the raw material for the formation of

dominance hierarchies among chipmunks on neutral ground in the lab (Wolfe, 1966) and in the

field. Data strongly support the notion that such

differences exist between age classes, with adults

dominating in encounters with juvenile neighbors

at all locations except close to the juvenile's burrow.

Evidence was also provided for age class, and

possibly individual, recognition that results in differential responses of residents toward different intruders at the same location. Thus, learned hierarchial relationships may exist in the population

between neighboring pairs as it relates to the delineation of boundary zones.

Predispersal Social Behavior in the Litter

The eastern chipmunk exhibits no long-term

associations between members of the mother-litter

unit after the litter's emergence above ground.

Occasionally, the mother deposits her litter in a

separate burrow at weaning time and has little to

do with them thereafter (see "Juvenile Emergence").

When the litter does emerge from the mother's

home burrow, associations are still quite transitory, the litter members growing intolerant of one

another and dispersing within two weeks time.

However, biologically important behaviors occur

during the short and transitory predispersal period

that are not observed at any other time in the life

cycle of the chipmunk.

Few investigators have observed predispersal

interactions between the mother and her litter, or

among littermates. Thoreau (1906) appears to have

been one of the first, noting in his Journal on 25

June 1858:

Sitting on Conantum house sill, I see two and perhaps

three young striped squirrels, two-thirds grown, within fifteen

or twenty feet, one or more on the wall and another on the

ground ... . Several times I saw two approach each other

and playfully and, as it were, affectionately put their paws

and noses to each other's faces. Yet this was done very deliberately and affectionately. There was no rudeness nor excessive activity in the sport. At length, the old one appears,

larger and much more bluish, and shy, and . . . calls the

others gradually to her and draws them off along the way,

they from time to time frisking ahead of her, then she ahead

of them.

More recently, Henisch and Henisch (1974) provided further descriptions of the short interactive

phase, describing cohesive, contact-promoting behaviors between individuals in the mother-litter

unit. The Henisches, like Thoreau, observed wild

chipmunks.

I made observations of litters emerging onto the

study plot from mid to late September of 1973 and

1974, the litters resulting from mid-summer breeding activities during both years (see "Mating Behavior"). Nearly all my observations of juvenile

social interactions during the predispersal phase

were of unmarked individuals. Hence, my descriptions do not distinguish between the sexes of littermates. My observations were intermittent and opportunistic, as the juveniles were sensitive to my

presence during the first week after emergence and

often retreated into logs or into the litter burrow

upon my approach.

I gathered further data during the spring of 1975.

The chipmunks apparently bred in late winter

during that year, and litters emerged onto the

study plot in mid-May. I observed one litter in

considerable detail and I made a photographic

study of behavior between the littermates using a

remote-control 35 mm camera setup. I later traced

these photographs to provide pictorial representations of behavior.

The following description is an amalgamation of

my notes on litter behavior, most being derived

from observation of three litters. I have constructed

a diagram (Figure 28) from my notes that indicates

the times at which certain behaviors appear or disappear in relation to emergence time.

During the several days following emergence,

young chipmunks rarely venture beyond 6-9 meters

from their burrows. Any disturbance usually sends

them retreating quickly into the litter burrow.

Littermates appear somewhat synchronized in their
42

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

-) dispersal and establishment (with defense)

of home ranges by juveniles

aggressive behavior among littermates

cohesive behavior among littermates

cohesive behavior between mother and litter, mother intolerant thereafter

increased transport of nest material by mother into burrow

(only for mothers whose litters emerged from home burrow)

I

5 10 15 20

DAY S

emergence

time

FIGURE 28.—Occurrence of major behavioral types in relation to emergence time of juveniles.

activities. I often observed them leaving the litter

burrow as a group, sometimes sitting together at

the entrance before beginning exploratory treks

(Figure 29).

The small band usually dissolves as the juveniles

move from the burrow, each moving off in a different direction, tasting and nibbling a variety of

objects (most of them inedible) found in the leaf

litter. Although the juveniles explore in a solitary

fashion, a loose grouping is evident at times. The

juveniles often make directed approaches toward

one another and exhibit contact-promoting behaviors. Sometimes, pairs move about together for

short periods before disbanding again to explore

by themselves. Further, littermates periodically

group together for short periods at certain favored

locations near the litter burrow (Figure 30).

Interactions with the mother are not common.

The juveniles show some tendency to follow their

mother during her foraging treks. The mother,

however, usually leaves the home burrow quickly,

leaving the youngsters behind in her home range

center. It appears that the mother makes a distinct

effort to avoid being followed and harassed by her

young. I observed no cases similar to that reported

by Thoreau, where the mother intercepted her litter and led them about. For the most part, the

mother avoids her young above ground and there is

little indication that juveniles learn proper foraging behavior by following her about. However, I

noted one exceptional case.

One juvenile was following its mother closely

while the mother was foraging in her home range

center. When the mother, with her cheek pouches

full of seeds, perched motionless on a small log, the

youngster nosed about her mouth, apparently trying to remove seeds or induce its mother to give

up a few. The juvenile tried squeezing its mother's

pouch with his forelimbs but was unable to remove

any seeds. Similar observations were made by

Henisch and Henisch (1974). They observed identical begging behavior, and, on occasion, noted

the mother to pass food to youngsters. Transfer of

food items from the mother's pouch to the young

might be of common occurrence in the natal burrow during the days preceding emergence, allowing

the young to taste and handle edible food items

from their mother's home range. Social interactions

occurring in the burrow between the mother and

her litter have not been investigated.

Although interactions with the mother are not

common, the mother may approach and investi-
NUMBER 265

43

FIGURE 29.—Two littermates examining their surroundings at the burrow entrance before

beginning an exploratory trek.

gate her young in a friendly manner when she encounters them. I noted several cases where the

mother approached and sniffed about the nose and

mouth region of intercepted juveniles, before moving on and resuming foraging activities.

After the initial 2-A day period, the mother begins to show considerable intolerance toward her

young and aggressively chases them for short distances, or snaps at them, if she encounters them

near her home range center. Chases of juveniles by

mothers (or neighboring adults) did not appear

as long or as highly aggressive as chases between

adults. It appeared to me that it would be an easy

matter for the mother, or any adult, to chase down

and kill a newly emerged juvenile. The juveniles,

although well-furred and adult-like in appearance,

are noticeably smaller (Table 14) and cannot move

as fast as adults through the leaf litter.

Intolerance by the mother towards her young

above ground occurs before dispersal, often when

the young are still living in the mother's burrow.

This raises questions concerning how the group

manages to live amicably in the same burrow system. My observations on the collection of nest

material by mothers may shed light on this problem. At emergence time, mothers whose litters

emerge from their home burrow collect large quantities of nest material (dried leaves) and transport

them into the burrow (Figure 31). It is possible

that the female, rather than expanding her own

nest to accommodate the young, builds a special

nesting cavity in her burrow system for the juveniles. She might even partition her burrow in some

way to avoid social interaction. However, the young
44

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 30.—Littermates exhibiting social tolerance at a gathering spot.

may still use the same burrow entrance as the

mother. Those mothers that transport their litters

to alternate burrow systems at emergence time

avoid social contact by isolation. It is probable that

this phase of avoidance coincides with weaning in

the species.

Littermates are quite amicable towards one another during the first week after emergence and

direct contact-promoting behaviors toward one another, even after the mother has become intolerant

towards them. The juveniles interact either by intercepting each other during exploratory trips, or

by periodically gathering at favored locations within

6-9 m of the burrow. During the spring of 1975, I

observed one litter to frequently visit a spot around

a large hollow log. By aiming a remote-control
NUMBER 265

45

FIGURE 31.—A mother hauling nest material (crushed leaves) into her home burrow just prior

to the emergence of her litter from the burrow.

camera at this spot, I obtained closeups of social

interactions (Figures 30, 37). From these closeups, I derived the drawings in Figures 32—36, 38.

The friendly relations of littermates are inferred

from their tendency to group together. Littermates

approach one another and sit together, often in

contact, and observe their surroundings (Figure 30).

Nasal investigation is common, two juveniles making contact with their noses and sniffing about each

other's nose or mouth region (Figure 32). Sometimes, they press their mouth regions close together,

tilting their heads from side to side, apparently

tasting one another by oral investigation (Figure

32e). This may grade into a general nasal and oral

investigation of the forehead, eye, or neck region,

that often includes nibbling of the fur with the

mouth (Figure 33). Sometimes, one individual will

nuzzle another by placing his nose to the throat

and sitting motionless, often with her eyes closed

(Figures 32 b, 34).

Most investigation between littermates is directed

towards the anterior end of the body; however,

some interest in the rear portions occurs. I observed

juveniles sniffing at the thigh region or nasally (and

perhaps orally) investigating the anal region of a

littermate (Figure 35). Mounting also occurs, where

one individuals climbs up another's back from the

rear, and grasps with its forelimbs in a manner

reminiscent of the adult copulatory pose (Figure

36). Such "sexual play" has been observed among

juveniles of other sciurids (C. C. Smith, 1968:42;

Horwich, 1972:21). I noted no definite thrusting

movements during sexual play. Since juveniles were

unmarked, I could not differentiate the roles of

the sexes in this behavior.

All of the forementioned behaviors between littermates appear to be friendly and do not result in

the retreat of one juvenile from another. They are

therefore inferred to be of a contact-promoting

nature, and can be contrasted with the typical adult

agonistic behaviors described earlier (see "AdultAdult Social Interactions").

Other behaviors occur between littermates that

are not so obviously amicable. Littermates may rear
46

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Vk3-i

a

b

FIGURE 32.—Nasal investigation among Httermates: a-d, nasal investigation e, naso-oral

investigation.
NUMBER 265 47

FIGURE 33.—Investigation of head and neck region of littermates.
48

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 34.—Nuzzling between littermates by one burying his

nose in the neck region of another.

up, and, balanced on their hind legs, "box" at one

another with their forepaws (Figures 37, 38). Usually the boxing is very light, with the two participants periodically pausing motionless for several

seconds before lightly boxing one another again.

On most occasions, boxing does not result in displacement, but is followed by contact-promoting

behaviors.

As the juveniles grow older, boxing may acquire

agonistic elements and grade into other aggressive

behaviors. Sometimes, one participant knocks another off a perch, to which the displaced individual

vocalizes in response. Boxing may also be followed

by aggressive snapping, a behavior having definite

aggressive elements and appearing identical to adult

snapping (Figure 19). At other times, boxing grades

into a roll-tumble fight (Figure 22), followed by a

short aggressive chase. It is probable that the development of aggressive behavior and intolerance between littermates is an important factor influencing dispersal from the litter burrow. Once dispersed,

juveniles exhibit adult-like agonistic defense of the

area around newly acquired burrow systems. Many

juveniles are defending such home range centers

within 15-18 days after their emergence.

I observed interactions between youngsters and

adult neighbors when juveniles intruded into the

home range centers of adult neighbors. Intrusions

were common during the latter part of the predispersal stage, when juveniles were regularly exploring beyond their mother's home range center. A

resident adult, becoming aware of an intruding

juvenile, approaches and aggressively chases the

juvenile from the area. Usually, the juvenile vocalizes loudly, especially if the charging adult makes

physical contact with him. The vocalization occurring at this time is a low pitched "squealing" that

is radically different than the high-frequency "chiptrill" (Dunford, 1970:224-225) that often accompanies adult-adult aggressive chases. It is possible

that the "squealing" vocalization (and perhaps the

small size of the youngster) enables adults to recognize the intruder as a juvenile, leading to reduced

levels of aggressiveness in the adult. Chases of predispersal juveniles by adults were unusually short,

and the adults never noticeably harmed juveniles,

even though the youngsters were easily overtaken in

most cases. The "squealing" vocalization is not

common in postdispersal juveniles, and chases with

adults at that time are noticeably more aggressive.
NUMBER 265 49

FIGURE 35.—Naso-anal investigation between littermates.

I made only one authenticated observation of

interaction between predispersal juveniles of different litters. Two juveniles of nearly the same age,

from litters of neighboring females, approached

one another on a log midway between their litter

burrows. The two juveniles touched noses (Figure

32a) and locked mouths for an instant (Figure 32e).

Both juveniles then instantly leaped backwards

through the air and retreated from one another in

haste. Apparently, both were startled and frightened when they did not recognize one another's

scent and /or taste, even though both appeared to

have amicable intentions at the start of the mutual

investigation.

A similar interaction occurred between the

mother of one litter and a juvenile from the litter

of a neighboring female. The mother and the juvenile met midway between their burrows. She apFIGURE 36.—Sexual play between littermates.
50

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 37.—Two littermates play-fighting while a third one watches.
NUMBER 265 51

FIGURE 38.—Play-fighting or boxing between two littermates

(top pair traced from Figure 37).

proached the strange juvenile, perhaps to ascertain

if it was a member of her litter, and investigated

its nasal region with her nose. The juvenile immediately leaped backwards and retreated, probably

startled by the strange scent/taste of the adult. The

mother did not appear startled, and, after a pause,

returned to her home range center.

Although agonistic behavior may occur among

littermates prior to dispersal, the broad range of

contact-promoting behaviors that occur is striking.

Cohesive behavior patterns have been described

for other rodent juveniles during the postweaning

period (Barnett, 1958:126; Balph and Stokes, 1963:

123; Wilson, 1973:47-52; Steiner, 1970:33-34; King,

1955:68-69) and it has been hypothesized that such

play behavior is critical in the development of

adult social and sexual behaviors (Wilson, 1973:

59-60). The function of the intra-litter social behaviors in chipmunks was not obvious, but it was

apparent that the predispersal phase provided a

rich social milieu of mutual investigation prior to

the development of the aggression and intolerance

that typifies adult behavior. The intolerance of

mothers toward their litters shortly after emergence

and the subsequent development of intolerance in

the young probably constitute the major stimuli

eliciting dispersal into the surrounding habitat.

Mating Behavior

The dynamics of mating behavior in the eastern

chipmunk have never been described in detail. This

seems strange, since the chipmunk is both common

and diurnal, a likely candidate for field-oriented

studies. Recent investigations have provided information related to breeding habits. Smith and Smith

(1972) and Pidduck and Falls (1973) discussed reproductive biology, concentrating on the delineation of breeding seasons. Another study by Smith

and Smith (1975) described the physical correlates

of estrus in the female. Isolated cases of copulation

have also been described (Smith and Smith, 1975:

762-763; Henisch and Henisch, 1974:78-84); however, no studies to date have provided descriptive

accounts of behavioral interactions between the female and her male consorts during the estrus

period.

My study will help fill that gap by providing

descriptions, gathered in the field, of intermale

competition and copulatory behavior during the

female's estrus period. To my knowledge, only one

other naturalist has published a realistic account of

the state of affairs during estrus. Burroughs (1904:

156) had the following to say about a breeding

female:

A single female will attract all the males in the vicinity.

One early March day I was at work for several hours near a

stone fence, where a female had apparently taken up her

quarters. What a train of suitors she had that day! How they

hurried up and down, often giving each other a spiteful slap

or bite as they passed.

As will be seen from my descriptions, Burrough's

short statement reveals many essential points concerning mating behavior in the eastern chipmunk.

This study was conducted from mid-June through

mid-July, 1974, on my Adirondack study plot. During 1974, breeding only occurred during the midsummer period. Nearly all chipmunks utilizing my
52

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

study plot were marked (see "Spatial Use"). However, during the breeding period, unmarked males

from off my study plot commonly invaded the

home ranges of estrus females on the plot, making

the identification of some males impossible. I located estrus females by checking the home range

sites of all females utilizing the study plot several

times each morning. Estrus was indicated by the

presence of several to many males on the home

range of a female, moving about in apparent efforts

to locate her whereabouts. If more than one female

showed signs of estrus, I concentrated my attention

on one of them. However, I periodically made short

trips across die study area to verify estrus activity

in the other females and to identify their male

suitors.

SOCIAL STRUCTURE PRIOR TO BREEDING SEASON

Prior to the breeding season, individuals of both

sexes are solitary and inhabit exclusive burrow systems (see "Adult Patterns during Spring and Early

Summer"), and both sexes aggressively defend the

central portions of their home ranges from intruding conspecifics (see "Adult—Adult Social Interactions"). Long distance excursions, by either sex, out

of the normal home range limits (Figure 12) are

rare during nonbreeding periods. As breeding season approaches, however, some males begin making long treks, 60-90 m, from their home range

centers to check on the reproductive condition of

females. I noted such movements by mid-June of

1974, 2-3 weeks prior to estrus in the population.

At this time, males typically invade the home range

centers of females and make directed approaches

toward the resident individuals. The females, when

not in breeding condition, aggressively chase away

the intruding males. Some males are persistent,

tolerating several chases in succession before leaving the female alone. When females begin coming

into estrus, nearly all males in the population make

lengthy excursions and group on the home ranges

of the estrus females. Such interactions with females

prior to estrus probably allow males to predict when

receptivity will occur.

GENERAL DESCRIPTION OF MATING BOUTS

I define the grouping of male suitors around

estrus females on their home ranges as "mating

bouts" after Farentinos (1972:318). I observed mating bouts for a total of nine females from 4 to 12

July 1974. The dates of estrus of the different females are included in Table 16. I kept close watch

on the study grid and the surrounding area from

early May until late July, and no mating bouts

occurred outside of the interval indicated. These

data point to considerable synchrony in the occurrence of summer estrus, all breeding taking place

within an eight day period. As noted in Table 16,

on two days (6 and 8 July), two or more females

were in estrus at the same time on the study area.

I noted mating bout activity as early as 8:30

A.M., but none persisted beyond 2:30 P.M. In no

case was a female involved in a mating bout on

more than one day. These data indicate that summer estrus occurs on a single day and lasts from

early morning to early afternoon, a duration of

around 614 hours. The following description is an

integration of observations from the nine mating

bouts that I followed. The structuring was similar

for all the mating bouts, allowing for a generalized

description. I include shorthand terms for some

behavior patterns in parentheses to facilitate discussion of mating chase dynamics later in this

report.

During the mating bout period, I found up to

12 adult males searching for the female on her

range (Table 16). The number I observed was

normally less than 12, especially on days when several females were in estrus at the same time on

the study site. Male composition changed on these

days as males switched from one mating bout to

another. While searching for the female, males

commonly interacted with one another. The usual

outcome of such interactions took the form of

either mutual avoidance, one-sided avoidance

where one male moved out of the padi of another,

or short aggressive chases. It appeared that the

males were more interested in locating the female

than driving away other males, hence agonistic

chases were elicited only when two males happened

into close proximity of one another.

Once I located a mating bout, I spent a considerable period of time searching for the female. The

majority of the males seemed to be unaware of the

female's whereabouts, although search behavior was

apparent. They spent most of their time investigating stumps, fallen logs, and hollows on the female's

home range. I usually spotted the female running
NUMBER 265 53

quickly out of a cavity or along a fallen log with

several males in pursuit. Her movements were very

quick and it soon became apparent that most of

her efforts were directed towards losing her male

pursuers. She often entered .cavities in stumps and

logs and then escaped out of alternate entrances,

leaving the males preoccupied with searching for

her in the cavity. In addition, she often stopped

abruptly in the leaf litter and let the males run

past her, whereupon she reversed her direction and

moved quickly to other isolated positions. These

deceptive antics were delightful to watch and the

female was often successful in losing me along with

her male chipmunk pursuers.

Usually, the males were able to eventually relocate the female by "sniffing" along her fresh path,

even when she was not visible to them. Apparently,

females secrete potent substances during estrus,

probably from the vaginal area, that result in a

"scent trail" wherever they proceed. However, from

my observation it appeared that the female's scent

trail had a limited life span. If the female managed

to throw off her pursuers for one or two minutes,

their abilities to utilize her trail decreased

markedly. Probably, the strength of the trail decreased to the point that it could not be distinguished from older trails left during earlier stages

of estrus. Having eluded the males, the female usually sat alone on a log or stump and groomed.

Often, during this period, the female was approached by a single male that managed to locate

her. Usually, the male approached the estrus female cautiously, with his tail held straight up in a

vertical position. The tail was then vibrated rapidly

from side to side, often in short bursts coinciding

with forward movements. This behavior (tail flicking) did not occur outside the breeding season or

outside the context described. The female was often

aggressive toward the approaching male. She sometimes vocalized loudly and snapped at him or

chased him away. Aggressive chases were followed

by a quick retreat from the area (bolting) as the

female attempted to isolate herself again.

If the female did not move away from the approaching male, the male then sniffed and/or licked

the vaginal area of the female (vaginal sniff). The

female then turned to investigate the male, resulting in mutual contact of the nose and mouth regions (kiss). These two behavior patterns were

sometimes omitted from the mating sequence. The

male then mounted the female by crawling on her

back and grasping with his forelegs just beneath

her forelegs. The female either tolerated his behavior or attempted to shake him off and bolt. If

he remained mounted, he inserted his penis and

began thrusting. The thrusting was very rapid and

occurred in spurts lasting around three seconds

each. If the female tolerated mounting, the male

performed ten or more of the short spurts of thrusting and then remained motionless on the female

for one or two minutes. Presumably, he was ejaculating at this time because abdominal contractions

were evident. The contractions were accompanied

by synchronous jerks of the hindquarters and bobs

of the head. Some further thrusting occurred intermittently. The female then broke from the male by

shaking him loose. She sometimes even chased her

male consort away, or snapped at him right after

copulation was terminated. On several occasions,

she bolted from the area while the male's locomotor abilities were depressed following ejaculation.

Usually, however, both members of the pair sat

near one another after copulation and began grooming.

The female groomed her vaginal area and her

whole body, while the male concentrated on licking his penis. The male also showed other behaviors that are probably indicative of his preceding

ejaculation. He often appeared to walk as if his

hind quarters were partially paralyzed and as if he

had to drag his rear along (slow walk); or he remained motionless with his abdomen flat against

the substrate and his tail curled under into a circle

in the vertical plane. The tail was then moved

slowly from side to side as if it were being rotated

on its base (tail rotation).

Copulation usually took place in a cavity where

the pair could not be observed. The male sometimes mounted the female in the open, but even

then she attempted to drag him into a cavity or

under a fallen log. My descriptions of thrusting

and ejaculation come from several cases where copulating pairs were visible.

After sitting and grooming for several minutes

(the male often sat motionless with his eyes closed

at this time), the pair rarely retreated back into

the cavity to copulate for a second time. Usually,

however, copulating pairs were interrupted by the

arrival of another male who had located their

whereabouts. The intrusion of another male (inter-
54

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ference) invariably put an end to the copulation in

progress. Either the intruder pounced on the back

of the mounted male or the consort dismounted

and attempted to drive away the intruder. In either

case, intensely aggressive fights occurred between

the contending males. The males grasped one another and rolled around on the ground for several

seconds, biting and scratching one another (Figure

22). I never noted any serious injuries as an outcome of such fights.

While the contending males were engaged with

one another, the female usually bolted, leaving

both males behind. Only rarely did the female

remain in the cavity while the males interacted aggressively. Often, the male who was interrupted

while copulating became intensely excited when he

returned to the cavity and found the female missing. He ran about, vocalizing loudly, and chased

any males that approached the site (broken-copulation fit).

The sequence of (1) isolation of the female, (2)

approach by a single male, and (3) copulation with

or without interference by other males, was a recurring cycle in the mating bout. The complete estrus

period (6i/2 hours) was composed of many of these

cycles. Complete copulations only occurred if the

pair remained isolated for two or three minutes.

In few cases did the female remain in one spot for

long periods when more than one male was in close

proximity to her. Towards the end of the estrus

period, the males seemed to show less interest in

the female, fewer males were involved in the mating

bout, and the female seemed to be more aggressive

towards approaching males, even if they were alone.

By 2:30 P.M., males showed no interest in the female and no congregation of males were found on

her home range.

MALE PARTICIPATION IN MATING BOUTS

Table 16 presents data concerning male participants involved in the nine mating bouts I observed.

TABLE 16.—Male participation in mating chases of nine females on

during early July 1974 (no females in estrus observed on 5, 7, or

the study plot

10 July)

Date of

estrus

k Jul

6 Jul

8 Jul

9 Jul

11 Jul

12 Jul

Observation

duration

(hours)

3

1.2

1

0.5

h.5

0.08

0.17

0.25

1.5

Female

in estrus

30

15

53

55

22

kS

h5

Unmarked

50

Participating

males

2, 6, 16, 18, 2k,

37, k6, 57, 60,

67, 2 unmarked

6, 7, 16, 18, 2k,

2k, 37, k6, 57,

2 unmarked

16, 18, 37, k6,

k unmarked

2k, 37, 1*6, 60,

k unmarked

2, 6, 16, 2k, 1*6,

51, 58, 60, 67,

3 unmarked

18, 2k, many

unmarked

6, 2k, 51, many

unmarked

6, 18, 2k, 67,

5 unmarked

2k, 58,

2 unmarked

Minimum

no. of males

part ic ipat ing

12

10

8

8

12

Not

estimated

Not

estimated

9

k
NUMBER 265 55

None of the females was observed continuously

through the complete mating bout (except perhaps 922); therefore, the lists of male participants

represent minimum values. I observed 9 22 and

9 30 for long periods of time and I feel that most

of the male participants in these bouts were

spotted. Another limitation is that unmarked males

from off the study area often were involved in the

bouts, especially when the female's home range

was on the periphery of the study area. These males

could not be distinguished from one another, but

I did attempt to estimate their numbers. It appeared that most mating bouts were composed of

8 to 12 males or more. The only exception to this

was the mating bout of 9 50, whose estrus occurred

late in the season on 12 July. She seemed to have

no more than four males pursuing her during my

1^2 hours of observation.

On 6 and 8 July, two or more females were in

estrus on the same day. On these days, some males

participated in more than one mating bout. On

6 July, cf 37 and cf 46 were involved in three bouts

while c? 16, cf 18, and o*24 participated in at least

two. On 8 July, cf24 was involved in two bouts.

Male switching is probably common whenever several females are in estrus in a particular area on

the same day.

The males listed for each mating bout in Table

16 were usually not involved in the individual

mating bouts simultaneously. Some males disappeared for varying periods of time and then suddenly reappeared at a later time. My efforts were

directed at following the female, hence it was difficult for me to determine the sum total of males

on her home range at any given instant. However,

in the case of 915, 922, and $30, I quickly tallied the males during the first ten minutes of observation and I found that at least 10, and 10 and

II males, respectively, were participating simultaneously in the bouts.

To approximate how far a male might travel to

join a mating bout, I calculated the distance from

the male's burrow location to estrus female's burrow location for all marked males in Table 16

whose burrows were known. The average distance

traveled was 57 m (±30) with a maximum recorded

distance 110 m for cf24 in 948's mating bout.

Comparing these distance values with the normal

extent of the home range during nonbreeding (Figure 12), it is apparent that males often travel well

beyond their neighbor's home range centers in

quest of estrus females. Assuming that males follow estrus females to the periphery of their home

ranges during mating bouts, movements by males

on the order of 135-150 m may occur during the

breeding season.

DOMINANCE HIERARCHIES AMONG MALES

The existence of dominance hierarchies among

males involved in mating bouts was examined during this study. While following individual estrus

females, I intermittently took notes concerning outcomes of male chases occurring in her immediate

vicinity. Figure 39 presents data derived from my

notes on three mating bouts, all on different days.

I recorded only eight chases during the mating

bout of 9 30. In seven, both participants were

known. These seven chases are represented in Fig39a. Admittedly, it is hard to construct a dominance hierarchy with confidence from so few chases.

However, when compared with data obtained from

mating bout of 9 22, close correspondence is obvious. Both mating bouts had similar participants

(Table 16), probably because 922 and 9 30 were

neighbors with a distance of only 10 m between

their home burrows. A chase diagram of marked

males participating in 9 22's mating bout is presented in Figure 396, along with a table including

chases involving unmarked males. Note especially

that cf24 initiated the greatest number of chases

(18) but that he was never chased by other individuals, marked or unmarked. Male 16 also initiated

a large number of chases (13), but cf 24 was clearly

dominant over cf 16 and chased him at least five

times. Comparing the chase diagrams of 9^0 and

922 (Figure 39a, b), note the striking similarity,

especially with regard to the males common to

both bouts (c?6, ^16, cf24, cf6O).

On 6 July, during the mating bout of 9 15 (a

neighbor of both 9 22 and 9 30), I recorded a total

of 16 chases involving at least one marked animal.

In 12 of these chases, both participants were

known. The chase diagram (Figure 39c) is again

similar to those for the other two mating chases

in that cf6, cf 16, and cf24, have the same dominance relationships. However, cf 18, who did not

participate to any great extent in the mating bouts

of 9 22 and 9 30, shows clear dominance over cf 24.

cf 18 initiated a total of 10 chases and was never
56

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

El

^7 C?24

3

c?60

I]

c516

d»6

cT37

lf2l cT57

E

[I

c?24

(J60

n

c?16

a

I]

c?6

^^»|(J4 6

CHASEE

<?24

d"l6

<*6

(?60

<?46

<?5I

s

(f24

\

-

-

-

-

-

-

0

5

\

-

-

-

-

-

5

4

3

\

2

-

-

2

11

<?60

-

-

-

\

-

-

1

1

d*46

-

1

4

-

-

-

5

-

-

-

-

-

\

-

0

&

k

9

9

5

2

-

2

\

27

\

18

13

9

4

0

2

3

49

E

[I

c?18

Hf

c?24

3

w

<*16

c?6

(?67

CHASEE

<?24

(?67

«?6

<?I6

«fie

\

-

-

-

-

0

<?24

5

\

-

-

5

<?67

3

-

\

-

-

3

1

2

-

-

3

rf!6

-

1

-

-

\

1

u df3^

1

3

-

-

-

\

4

\

10

6

0

0

0

0

16

a D c

FIGURE 39.—Dominance hierarchies among males involved in the mating bouts of $ 15, $ 22,

and $ 30 (top, results of aggressive displacement chases among marked individuals; bottom,

interactions among marked males as well as with unmarked (umk) males; see Table 16): a,

mating bout of $ 30 (matrix not included because only one chase was recorded with an

unmarked $); b, mating bout of $ 22; c, mating bout of $ 15.

chased. cf24 initiated a total of 6 chases, but he

was chased by cf 18 five times.

These data indicate that linear dominance hierarchies defined by the outcomes of aggressive displacement chases may exist during mating bouts.

Furthermore, the hierarchies may remain relatively

stable from day to day if the spatial position of

the mating bouts and the identity of the male participants do not change radically.

FINE STRUCTURE OF MATING BOUTS

I observed two mating bouts for a sufficient length

of time to do fine-grained analysis of mating dynamics (Table 16). I followed 9 30 almost continuously from 11:00 A.M. to 2:09 P.M. on 4 July, a

total of 3 hours of direct observation. Her mating bout probably began around 8:30 A.M. Therefore, data are missing for the first 214 hours of the

mating bout. I monitored the mating bout of 9 22

almost continuously from 9:00 A.M. to 2:29 P.M.,

on 8 July producing a total of nearly 4i^ hours

of direct observation.

A great many difficulties are encountered when

the data from these mating bouts are analyzed. A

major problem is determining when copulations

actually occurred. Since the female usually disappeared into a cavity with individual males, I rarely
NUMBER 265 57

observed directly the mounting, thrusting, and ejaculation. If the copulation comes to a natural termination (no interference by other males), ejaculation may be inferred by the presence of abdominal

contractions, penis licking, the slow walk, or tail

rotation by the male. In many cases, however, the

female bolted after spending several minutes in the

cavity with a male, leaving no time for me to observe behavioral indicators in the male. In other

cases, the pair was interrupted by another male,

forcing the female to bolt from the area and engaging the male in immediate aggressive dispute. In

these cases too, I did not know for certain if ejaculation, or even mounting and thrusting, had occurred.

From my several observations in the open of

mounting, thrusting, and abdominal contractions,

it was apparent that ejaculation could occur within

30 seconds after mounting. For this reason, if I

noted the female to be alone in a cavity with a

male for over 30 seconds, then copulation with

ejaculation was deemed possible. A further complication was that a single male may copulate and

ejaculate several times with a female over a short

period of time. I observed three successive copulations by one male over a 25 minute period. This

means that prolonged association of a male with a

female in a cavity may result in more than one

ejaculation. Of course, there is no way to determine

this unless the pair is observed directly. These

problems make the interpretation of my notes exceedingly difficult and subject to error.

A condensed version of my field notes for $ 30's

mating bout is presented in Table 17 (3 hours direct observation). This version includes almost all

situations where I noted males to disappear into

cavities with the female or to mount and attempt

to copulate in the open. The information that I

have omitted consists mainly of descriptions of male

pursuit while the female was bolting or was employing deceptive tactics to isolate herself, and descriptions of short associations with individual

males that were either interrupted by other males

or quickly terminated by the female. In nearly

every copulatory situation described in my notes,

the female had isolated herself from the male pursuers and was sitting alone, either in a cavity or on

a stump or log, before being approached by a single

male.

A reading through the condensed notes indicates

several major points. First, ten copulatory situations

are listed where copulation was deemed possible.

Actual indication of ejaculation (penis licking

in this case) occurred in copulatory situations 3, 4,

5, 6, and 10. Mounting or mounting with thrusting was directly observed in copulatory situations

3, 7, 8, 9, and 10. In copulatory situations 1 and 2,

I inferred copulation only from the long time periods that the female spent in the cavities with the

males. I did not observe other indicators of ejaculation, such as abdominal contractions, the slow

walk, or tail rotation in $ 30's mating bout. Her

mating bout, however, was the first that I monitored and it is probable that I was not sensitive

to the occurrence of some of these patterns. The

efficiency of my observations increased for subsequent mating bouts.

The three successive copulatory situations of c? 16

(3, 4, 5) demonstrate that individual males are able

to copulate and probably ejaculate (I noted penis

licking in all three cases) several times with a female in a short period of time (25 minutes). Based

on this evidence, it is possible that several copulations could have occurred during the long time

intervals that $30 was alone with males during

copulatory situations 1 and 2. It appears, however,

that after each completed copulation, both participants come outside of the cavity to groom their

genitals, before entering the same or another cavity

to copulate again.

It is informative to compare the condensed notes

with the data on male dominance (Figure 39). If

the hierarchy is correct, we may expect most of

the mating to be carried out by the dominant cf 24

(c? 18 did not participate in this mating bout) or

by cf60 and <? 16, who appeared intermediate in

dominance. According to my data, both <5"24 and

cf60 probably copulated with $30 (copulatory

situations 1 and 6, respectively) but they did not

monopolize her during my observation interval.

Male 16 monopolized 9 30 for a short period of

time (25 minutes) and he managed to copulate

with her three times in succession during that period. More striking is that c?37 and <f 46 apparently copulated with $30. According to Figure

39a, b these males were low in the hierarchy.

Neither was ever observed to initiate aggressive displacement chases. Since no other females were in

estrus on 4 July (Table 16), this observation is not

complicated by problems associated with the switch-
58

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 17.—Condensed fieldnotes for mating chase of ? 30 on 4 July 1974

Copulatory

situation

Male

pursuer Time Comments

10

2k 11:00 a.m.

11:20

11:27

Jnmarked 11:32

11:36

11:50

16

16

16

60

2

37

12:00 noon

12:03 P.m.

12:06

12:12

12:13

12:17

12:21

12:25

12:1+3

12:1+7

12:51+

12:55

1:10

1:17

1+6

1:20

1:31

1:32

Unmarked 1:1+3

1:1+1+

1:1+6

2:02

9 enters cavity in top of stump

o* 2U enters cavity

o" 2k emerges and sits; 9 emerges and bolts

9 enters cavity in log

Unmarked a enters cavity followed by o" 37;

d" 37 comes out

d* 37 enters cavity; unmarked d" chases him out;

9 comes out and bolts

9 mounted by o" 16; they enter cavity at base

of a tree

9 bolts and enters another cavity; o" l6

follows her in

d* l6 out, licks penis; 9 appears at entrance,

then goes back in; d" 16 enters with tail

vibration; 9 bolts

9 enters cavity; o* 16 enters with tail vibration

9 out, enters another cavity; a 16 follows

o" 16 comes out and grooms penis

d" l6 enters same cavity but 9 bolts and enters

another cavity; d* 16 follows her in

d" 16 out, licks penis; then d* 60 approaches

and fights with a" 16; 9 bolts

a* 60 approaches 9 and they enter a cavity

d* 60 comes out, licks penis; o* 2k arrives

and chases d" 60 away; 9 bolts

9 approached by cf 2; 9 retreats into cavity

and is mounted by cf 2 with thrusting

d* 37 enters cavity and breaks copulation;

9 bolts

d" 37 approaches 9; they enter cavity

d* 37 out, 9 out; o" 37 mounts with thrusting;

9 drags him into a cavity

d* 2k enters cavity; all three come out;

9 bolts

9 mounted by d* 1+6 who approached with tail

vibration; he begins thrusting

Copulation broken up by other males; 9 bolts

Unmarked o" approaches with tail vibration,

sniffs 9's vagina and mounts; 9 shakes him

off and bolts

9 and unmarked d* enter a cavity

9 conies out and bolts; unmarked d" grooms

penis

9 enters nest and stays there; no dfcf noted

in her vicinity
NUMBER 265

59

ing of dominant males to other mating bouts

thereby leaving the subordinates to copulate with

the female. The data for 9 30, however, are complicated by the fact that I did not monitor the first

2i/£ hours of her mating bout.

The condensed version of 9 22's mating bout is

provided in Table 18. It contains the same omissions as those described for 9 30's condensed notes

(p. 57). Covering a long time period (4i/2 hours),

it became obvious that 9 22 had a great many copulatory situations (total of 26). In the first 13 instances, however, I noted no behavioral indications

of ejaculation. On the other hand, 11 of the last

13 attempts did include indicators. This leads me

to believe that many of the earlier situations probably did not result in ejaculations. The first attempted copulations that I observed during 9 22's

mating bout support this notion. Early in the mating bout I noted c?24 attempting to mount 9 22

on several occasions, but she always kept moving so

that he could not successfully grasp her. It appeared that she was purposely avoiding copulation

with the male at that time.

Basically, the form of the mating bout of 922

is similar to 9 30's in that a great many copulatory situations occurred with a wide variety of

males. The only verified case of successive copulatory attempts by the same male was in copulatory

situations 18 and 19 by <?46.

The effect of male dominance on copulation attempts in 9 22's mating bout is uncertain. The

dominant <^24 (Figure 396) monopolized 922

from 9:00 A.M. until 10:45 A.M., and he was responsible for 7 of the first copulatory situations.

However, I noted no behavioral indicators of ejaculation in cf24 during any of these instances. For

this reason, I am uncertain if any successful copulations occurred with cT24. Male 16, intermediate in

the hierarchy, was responsible for two copulatory

situations (3 and 7) where no indicators of ejaculation occurred and one situation (16) where I noted

penis licking. Male 6, a subordinate (Figure 39), was

responsible for three copulatory situations (13, 17,

20), two of them including behavioral indicators

of ejaculation. Male 46, another subordinate (Figure 396), had two copulatory situations (18 and 19)

with indicators of ejaculation. These data indicate

that subordinate males can, and do, copulate with

the female, at least during the last half of the mating bout.

A complicating factor in the interpretation of

the data for 9 22 is that another female (9 48) was

in estrus nearby at the same time (Table 16).

Furthermore, I noted c?24 in the vicinity of the

other female around 11:00 A.M., after his prolonged

association with 9 22. Male 24 was not involved

thereafter in 9 22's mating bout. Perhaps his absence allowed subordinate males to copulate more

freely with 9 22.

UTILIZATION OF HOME RANGE DURING ESTRUS

The female usually stays within her normal home

range boundaries (Figure 12) through the entire

mating bout. In order to quanitatively compare

home range utilization during non-estrus periods

with home range use during the mating bout, I

monitored spatial use activities prior to, during,

and shortly after the estrus period of 922. These

spatial use data for 9 22 are depicted in Figure 40.

I determined pre- and post-estrus spatial use patterns by methods described earlier, and the home

range diagrams in Figure 40a, b are identical to

those included in Figure 4a, b. Note that the general home range shapes, the geometric centers, and

the spatial use patterns were similar for the preand post-estrus periods.

Figure 40c, d presents movement data for the

estrus period derived from direct following during

estrus where I monitored time spent in each grid

square. Note that the geometric center calculated

from this data and the general spatial use pattern

during estrus correspond closely with the data derived from the pre- and post-estrus periods. This

leads to the conclusion that the estrus female utilizes her home range in a fairly normal fashion

during the mating bout. The average time spent

per grid square during estrus (1.1 minutes) was

lower than during the non-estrus periods (2.6 minutes), reflecting the fast movements of the female

when she was trying to lose pursuing males during

the mating bout. The difference, however, is not

significant because of the wide spread in the estrus

female's time values. When she became isolated

with single males after her fast movements, she

spent as long as 14 minutes at single locations.

The sites for the 26 copulatory situations during

9 22's mating bout are included in Figure 40d, I

did not map exact locations but I did note the grid

squares in which copulatory behavior occurred. The
60

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 18.—Condensed

Copulatorj

situation

1

2

3

1+

5

6

7

8

9

1 0

1 1

12

Male

pursuer

2k

Unmarked

16

21+

21+

2k

16

2k

Unmarked

2k

2k

Jnmarked

Time

9:00 a.

9:01

9:03

9:06

9:08

9:09

9:10

9:12

9:12|

9:13

9:15

9:17

9:19

9:20

9:1+1

9:1+7

10:01

10:05

10:06

10:07

10:13

10:11+

10:31+

10:35

10:38

10:1+2

10:1+3

10:1+5

11:11

11:12

fieldnotes for mating chase of 9 22 on 8 July 1974

Comments

m. 9 enters cavity with o" 2k

cf 2k appears at entrance

9 also at entrance; o* 2k tries to mount;

both go inside

9 at entrance; cf 2k trying to mount;

9 shakes him off

9 moves away from cavity; cf 2k follows;

o* 2k chases approaching o" l6; 9 bolts

Unmarked d" follows 9 into cavity

Unmarked o* comes out and sits, then goes

back in

9 out; unmarked cf out; they kiss, then

both go back in

cf 16 approaches and chases unmarked cf;

cf 16 enters cavity

cf 16 chases unmarked o" again; 9 bolts

cf 2k approaches with tai l vibration;

9 snaps; cf 2k follows and sniffs her vaginal

area; they enter cavity

Both out, sit together, both back in;

unmarked cf approaches; o* 2k chases him;

9 bolts

cf 2k and 9 enter cavity; a 2k out and chases

cf 6 away three times; 9 remains in cavity

Unmarked cf approaches; cf 2k chases him;

9 bolts

cf 2l+ enters base of stump with 9

cf 2k out and chases cf 16; 9 bolts; cf 2k has

broken copulation fit

cf 16 enters cavity with 9

cf 6 enters the cavity; cf 16 chases cf 6;

9 bolts; cf 16 has a broken copulation fit

cf 2k enters cavity with 9

9 comes out and bolts

Unmarked cf and 9 enter cavity together

cf 60 chases unmarked cf out of cavity;

9 bolts

cf 2k enters cavity with 9

Unmarked cf enters, then comes back out

cf 2k comes out and chases unmarked cf;

9 bolts; cf 2k has broken copulation fit

cf enters cavity with 9

cf 16 enters cavity; cf 2k chases cf 16 away

and reenters

cf 2k and 9 both out; 9 bolts; cf 2k has a

broken copulation fit

Unmarked cf approaches 9 with tai l vibration;

they enter a cavity

cf 60 enters; 9 bolts as cf 60 chases unmarked d
NUMBER 265 61

TABLE 18.—Continued

Copulatory

situation

13

Ik

15

16

17

18

19

20

2 1

22

23

2k

25

Male

pursuer

6

Unmarked

Unmarked

16

6

1+6

1+6

6

Unmarked

Unmarked

51

Unmarked

Unmarked

Time

11:15

11:16

11:35

11:38

11:1+2

11:1+6

11:57

12:01 p.m.

12:02

12:35

12:39

12: Ul

12:1+2

12:1+5

12:1+6

12:51

12:56

12:59

1:01

1:08

1:10

1:16

1:23

1:27

1:36

1:1+6

1:57

2:01

2:03

2:07

Comments

o" 6 enters cavity with 9

Unmarked cf enters; d 6 chases him; 9 bolts

9 goes into cavity with unmarked cf who

exhibits tai l vibration

Unmarked cf at entrance, exhibits tai l rotation

and licks penis; a" 16 chases unmarked cf away;

9 bolts

9 enters cavity with unmarked o"

9 bolts, then licks genitals

9 enters cavity with cf 16

o" 16 out, licks penis, chases unmarked cf

and reenters

o" 16 chases cf 6 who entered cavity; 9 bolts

cf 6 enters cavity with 9

o" 6 chases cf 1+6; cf 6 exhibits tai l rotation

and slow walk

Unmarked cf interferes; cf 6 chases him;

9 bolts

9 enters cavity with cf 1+6 who shows tai l

vibration

cf 1+6 noted mounted; cf 6 pounces them;

9 bolts

cf 1+6 mounts and 9 drags him into cavity

cf 1+6 out and licks penis; then goes back in

cf 1+6 out, licks penis; 9 comes out and grooms

cf 6 chases cf 1+6 away; 9 bolts; cf 1+6 has

broken copulation fit

9 enters cavity with cf 6

cf 6 and 9 out; cf 6 slow walks with a curled

tai l (no tai l rotation noted)

Unmarked cf approaches and chases cf 6; 9 bolts

Unmarked cf mounts with thrusting; after

15 seconds abdominal contractions noted;

cf 6 arrives and interferes; 9 bolts

9 enters cavity with unmarked cf

Both out; 9 bolts as another unmarked cf

approaches

9 enters base of tree with cf 51

Unmarked cf interferes; 9 bolts; cf 51 has

broken copulation fit

Unmarked cf mounts 9, 30 seconds of thrusting,

then abdominal contractions noted

9 breaks away; unmarked o" licks penis and

exhibits slow walk; 9 licks genitals

Unmarked cf approaches and 9 bolts

Unmarked cf mounts 9 under log with thrusting

followed by abdominal contractions and head

bobbing
62

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

C opulat ory

situation

26

Male

pursuer

67

Time

2:09

2:1k

2:17

2:28

2:29-3

TABLE 18.—Continued

Comments

9 shakes him off; he licks penis and 9 licks

her genitals and bolts

9 mounted by d 67 in the open, thrusting

followed by abdominal contractions

They break; 0" grooms penis; 9 grooms genitals;

they si t together

9 rushes off to chase 9 62 who was near

9 22's burrow

:00 No mating activity noted; observations

terminated

major point derived from these data is that copulations took place throughout $ 22's home range. In

her habitat there was an abundance of fallen logs

with cavities, making it possible for the female to

find a suitable site wherever she was approached by

single males.

A

2 1

1

. PRE-ESTRUS

2 2 4 5

2 15 3 22

1 19 II 1 2 8

II 47 2628 39 4

4540 7315, 6

5

4

7 8

M23I5 34992317 7

1 13 13 5013

1 4 13

5

4

POST-ESTRUS

I I

C. ESTRUS

1 I I

I 2 2 I K) I I

3 8 244 2 I

12 7 23 2 2 I I

3 4 4 O (4 I 14 I

2 8 3 235 8 I

14 I I 4 10

I

1

1 1

2 2

13

17

1 2 II 2

3 7 3 5

II 1 3821

8 6039 2

9 9 lfe 131

12 18 6

8 12

7

1 5

5 2222

7 2642 2429 9

1 12 8 2

4

1 4

D. COPULATION SITES

I I 2

2 2

I

FIGURE 40.—Home range use by $22: a, pre-estrus, 809 min

of following over 5 days (11-13, 16, 18 June), average time

spent per grid square 2.42 min; b, post-estrus, 799 min

of following over 3 days (9, 13, 14 July), average time spent

per grid square 290 min.; c, estrus, 247 min of following on

8 July, average time spent per grid square 1.10 min; d,

distribution of copulation sites through 247 min of following

during estrus. (a-c, numbers indicate total minutes spent in

each grid square; d, numbers indicate total instances each

site used on 8 July; solid circle = burrow location.)

I noted the same general form of home range

utilization during estrus and the same diversity of

copulation sites for most other estrus females observed. A notable exception, however, occurred in

two females whose home ranges were near a patch of

mixed forest beginning roughly 30 m off the east

end of the study area (Figure 41). This habitat

had a much denser undergrowth (primarily hobblebush, Viburunum alnifolium) than the beech-maple

climax forest on the study grid (see "Habitat

Analysis").

I watched the two females make periodic excursions into the mixed woods during their mating

bouts, even though these excursions took the females

off their normal home range and into habitat not

normally utilized by chipmunks. I feel that these

long distance jaunts were primarily used by the females as a means to lose pursuing males. Usually,

an estrus female would run into the mixed woods

and make a large circle, returning to her home

range after 1 to 2 minutes. I observed no copulations in the mixed woods during such jaunts.

MATING SYSTEMS OF OTHER SCIURIDS

Recent interest in the social behavior of members

of the family Sciuridae (squirrels) has generated an

abundance of data describing the mating habits

of various species. The pioneering study of the

black-tailed prairie dog (Cynomys ludovicianus) by

King (1955) described an interesting mating scheme

that has subsequently been found to occur in many

other ground-dwelling sciurids. The black-tailed

prairiedog towns are apparently organized into discrete spatial units (coteries), usually containing a
NUMBER 265

63

single adult male, several adult females, and immatures of both sexes. The coterie space is defended

from intruders by its occupants (especially the

adult male). During the breeding season, the adult

male mates with the females within his coterie with

little interference from neighboring males. The

system is thus a polygynous one where single males

monopolize and mate with several adult females.

A similar situation seems to exist among the

ground-dwelling marmots. Downhower and Armitage (1971) and Barash (1973) have described

polygynous groupings in the yellow-bellied marmot

(Marmota flaviventris) and the Olympic marmot

(Marmota olympus), respectively. A similar mating

system is also found in several spermophiles (ground

squirrels). Temporary polygynous groups, where

males defend areas enclosing a group of females

during breeding season only, have been described

for the arctic ground squirrel (Spermophilus undulatus) (Carl, 1971), and the Columbian ground

squirrel (Spermophilus columbianus) (Betts, 1973;

Steiner, 1970).

Studies on the arboreal sciurids, on the other

hand, have revealed a strikingly different pattern

of mating behavior. C. C. Smith (1968) described

mating in the red squirrel (Tamiasciurus hudsonicus) and the douglas squirrel (Tamiasciurus douglasi), who possess social systems where both sexes

defend individual and mutually exclusive territories on a year-round basis. When a female comes

into estrus, groups of males congregate on her territorry and compete for mating rights. The group of

males seems to follow the female about, hence this

form of mating behavior has been termed a "mating bout" (Farentinos, 1972:318). Smith noted that

one male was usually aggressively dominant over

other males involved in single mating bouts and

that the dominant was able to monopolize the female for considerable periods of time.

Mating systems have also been described for

Sciurus carolinensis, the eastern gray squirrel (Bakken, 1959; Horwich, 1972), and in Sciurus aberti,

the tassel-eared squirrel (Farentinos, 1972). During

the nonbreeding season, adults of both species occupy individual but broadly overlapping home

ranges. The males congregate and compete on the

female's home range during the day of estrus.

Dominance hierarchies among the males seem to

exist during mating bouts; however, the relationship between dominance and mating success in the

males is uncertain. Horwich (1972:62-69) and Farentinos (1972:322) noted that many copulations occurred with obviously subordinate males.

The differences between the polygynous mating

system found in many of the ground-dwelling sciurids (where discrete areas enclosing several adult

females are defended by single adult males prior

to and during a breeding season) is strikingly different from the mating bout systems described for

arboreal sciurids (where males compete for mating

rights on an individual female's home range only

during her estrus period). In the former system,

male dominance is highly correlated with mating

success and polygyny is the general rule. In the

latter system, male dominance may or may not be

highly correlated with reproductive success and it

remains unknown as to whether the system is effectively a polygynous one.

COMPARISON OF CHIPMUNK AND ARBOREAL

SCIURID MATING DYNAMICS

In general, the mating system of the eastern chipmunk closely resembles the mating bout systems

described for the arboreal sciurids. In both the

chipmunk and the arboreal squirrels, males congregate on the home range of the female during

the day of estrus, and compete with one another

for mating rights. Observations of aggressive displacement chases occurring between the males support the notion that dominance hierarchies exist

among the males during mating bouts. Though

the mating systems of the various species are alike

in many respects, differences are apparent. The

following discussion will provide fine-grained comparison of the arboreal sciurid and chipmunk mating systems.

The duration of the mating bout or estrus period

in the Adirondack eastern chipmunk (614 hours)

seems to be shorter than that noted in the arboreal

sciurids. Farentinos (1972) reports a mean duration of 11 hours for the tassel-eared squirrel, and

indicates that the chase lasts from early morning

until dusk. C. C. Smith (1968:37-38) describes the

mating bout in the red and douglas squirrels as

lasting for the greatest part of a day. The eastern

chipmunk is unique in that the mating bouts I

observed terminated by early afternoon. However,

there may be some variation among different chipmunk populations. Smith and Smith (1975:762)
64

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

estimated estrus in the eastern chipmunk to last

3-10 days. Unfortunately, they measured estrus by

the physical condition of the vagina in trapped

females, and not by the duration of behavioral

interactions between the sexes. Horwich (1972)

does not give estimates of estrus duration in the

gray squirrel, but he (1972:69) does indicate that

most males depart from the mating bout in its later

stages and a pairing of the female with a single

male occurs. I did not observe this phenomenon

of pairing in the eastern chipmunk. It is possible

that most male gray squirrels lose interest in the

female after she has passed peak estrus, thus leaving her to copulate with one or two subordinates

that could not gain access to her previously.

Although the number of males involved in chipmunk mating bouts varied, groups up to 12 males

are probably of common occurrence, and as many

as 10 males may be in close proximity to the female

at any one instant, C. C. Smith (1968) describes

mating bouts in red and douglas squirrels as involving 1-10 males. Horwich (1972) does not give

estimates for the gray squirrel, but Bakken (1959)

noted group sizes ranging from 3-14 males, at least

during the early stages of the mating bout. Farentinos (1972) observed six mating bouts in the tasseleared squirrel where the number of marked male

participants ranged from 6-11. He did not indicate

if unmarked males were present. These data indicate that the number of males participating in

mating bouts is variable but roughly the same for

all species exhibiting the mating bout type of mating system. It is reasonable, however, that the variables of population density and synchrony of estrus

have radical effects on group size in mating bouts.

Group size would probably decrease at low population densities or when female estrus periods are

so highly synchronized that many females in the

same vicinity are in estrus on the same day, thus

dividing the males between them.

The possible existence of sexual pheromones

released by the estrus female and used by males to

locate her during the mating chase is supported

by my own observations on the chipmunk and by

the observations of other investigators on the arboreal sciurids. All observations indicate that when

the female is not visible, the males move about

within her home range, nasally investigating objects in the environment in apparent attempts to

locate her position. In this manner, a female hidden from view is often located by the males. C. C.

Smith (1968:37) speaks of the possibility that female red and douglas squirrels emit pheromones

on the days approaching estrus such that neighboring males know beforehand when the estrus day

will occur. I have no definitive observations of

chipmunks to support this notion. Chipmunk males

however, did show an increased tendency to approach non-estrus females on their home ranges

during the two to three weeks prior to the breeding season. These were probably attempts to assess

the female's receptivity.

The synchrony of summer estrus and the lack of

spring breeding on my study area during 1973 and

1974 (spring breeding occurred in 1975) have not

been described for the eastern chipmunk at other

localities. Studies on chipmunk reproduction (Pidduck and Falls, 1973; Smith and Smith, 1972) have

indicated that spring breeding (February-April)

occurs in most populations while summer breeding

(June-August) is of variable occurrence. C. C. Smith

(1968:39-40) and Bakken (1959) indicate that two

breeding seasons commonly occur in the red, douglas, and eastern gray squirrels. Only one breeding

season (spring) has been reported for the tasseleared squirrel (Farentinos, 1972). Pidduck and

Falls (1973) monitored summer estrus in six eastern chipmunk females in Ontario and found the

estrus periods to be spread over a 25-day period,

while the nine breeding females on my study area

during 1974 were noted in estrus over an 8-day

period. My observations on litter emergence on the

study area in September of 1973 verified a summer breeding season for that year; they also indicated considerable synchrony as the litters of the

three females under observation emerged over a

3-day period (see "Juvenile Emergence"). Little data

on breeding synchrony among neighboring females

is available for the arboreal sciurids. However, Farentinos (1972) reports that the six mating bouts he

analyzed were spread over a 30-day period, indicating a reduced synchrony.

The tendency of chipmunk females to copulate

in cavities was obvious during my study. Red

squirrels show a trend toward copulation in cavities while douglas squirrels commonly copulate in

the open (Smith, 1968:38-39). Farentinos (1974)

indicates that copulation in the tassel-eared squirrel

is often in the open, usually on the trunks of trees.

Horwich (1972:63), on the other hand, indicates
NUMBER 265 65

that gray squirrels may copulate within nests. The

reluctance of the eastern chipmunk to use the home

burrow for copulation was notable during my study.

Perhaps the female does not want to advertize the

location of her burrow because it may lead to the

pilfering of her food hoards. Perhaps also, the female cannot copulate effectively if she finds herself

cornered by a large number of males in her burrow

system.

The advantages of copulating in cavities are

readily apparent. First, copulating pairs in the open

are quite vulnerable to predation, especially by

aerial predators; copulation in cavities obviates

this danger. Farentinos (1974) observed predation

by goshawks (Accipiter gentilis) oriented toward

males involved in the mating bouts of tassel-eared

squirrels. Likewise, I also noted goshawk predation

during a single mating bout in the chipmunk, although no animals were captured by the bird. Accipiters, hawks, and owls (owls are active during

darkly clouded days) may find chipmunks much

easier to capture during mating bouts because the

males are usually far off their normal ranges and

hence unaware of the locations of cavities and hollows in which to retreat. Further, the males are preoccupied with locating the estrus female. Chipmunk

males involved in mating bouts on the study area

often ran under my legs or across my boots without showing any awarnesses of my presence.

A further advantage of copulation in cavities

is that it decreases the likelihood that the copulating pair will be interrupted by the approach of

other males. I commonly observed cases where chipmunk males passed close to cavities enclosing the

copulating pair without locating them. It is my

feeling that the female probably is not able to copulate successfully if her location is known by more

than one male. Deceptive behaviors employed by

the estrus female to lose pursuing males, so common in chipmunk mating bouts, have not been

reported for the arboreal sciurids.

Aggressive chases are common among eastern

chipmunk and arboreal sciurid males involved in

mating bouts. Intensely aggressive fights between

males sometimes occur during chipmunk mating

bouts, but they are uncommon. Farentinos (1974)

describes fights between males in the tassel-eared

squirrel, but remarks that they are rare. Fighting

was not described for the other arboreal sciurids.

Tail flicking by the male when approaching

estrus females during a mating bout has been described by Farentinos (1974) and Horwich (1972:

62-69) for the tassel-eared and eastern gray squirrels, respectively. The chipmunk is unique in that

it holds its tail in a rigid vertical position during

tail flicking. Farentinos (1974) feels that tail flicking normally occurs in conflict situations that evoke

approach and avoidance tendencies. He observed

that tail flicking seemed to be specific to the mating

bout context and was not evoked by conflict situations outside of the breeding season.

Aggressiveness of the female towards approaching

males during estrus is common in chipmunks and

was also noted in the tassel-eared and eastern gray

squirrels by Farentinos (1972) and Horwich (1972:

62-69). Farentinos (1972:318, 322) observed that

female tassel-eared squirrels were very aggressive

toward the dominant male and most other males

involved in the mating bout, while she was obviously complacent toward certain subordinates. Horwich's (1972:66) observations that gray squirrel

females tended to pair and copulate with certain

subordinate males late in the mating bout may also

support the notion of differential treatment of males

by females. I noted no specific trends of differential

treatment of males by females in my study, although I observed that females readily accepted

some approaching males and aggressively repelled

and bolted from other approaching males.

A comparison of the fine structure of copulation

indicates similarities among the species. Vaginal

sniffing or licking just prior to mounting was seen

in male chipmunks, male gray squirrels (Bakken,

1959), and in male tassel-eared squirrels (Farentinos, 1972). Farentinos defined four copulation

phases in the tassel-eared squirred that closely resemble the phases I defined for the eastern chipmunk. There is an initial phase of rapid thrusting

followed by slower and deeper thrusting. The pair

then remains motionless as ejaculation is occurring.

Then the female pulls away. In chipmunks, ejaculation may be accompanied by abdominal contractions and head bobbing.

My observations of chipmunks indicate that the

ejaculation phase may be reached in around 30 seconds, after which the male remains mounted for

up to one to two minutes. A period of 30 seconds,

however, may be sufficient for insemination to occur. Farentinos (1972) calculated the mean duration of copulation in the tassel-eared squirrel to be
66

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

around 72 seconds. C. C. Smith (1968:38-39) noted

that male red and douglas squirrels often remained

mounted for a up to 4-8 minutes, but he did not

describe the various phases of copulation. Horwich

(1972:69) estimated that the entire copulation act

of gray squirrels lasts from 15-30 seconds, and he

reported no cases of extended copulation.

After the termination of copulation, nearly all

species exhibit genital grooming. C. C. Smith (1968:

38-39) observed extensive penis licking in male red

and douglas squirrels following copulation. Horwich (1972:67-68) also noted penis licking in gray

squirrel males and used it as an indicator that cop

ulation had occurred when the pair was in a cavity.

The male usually came out in the open and exhibited this behavior. Farentinos (1972) did not

describe postcopulatory grooming behavior in the

male tassel-eared squirrels. Penis licking was a

common male postcopulatory behavior in the

eastern chipmunk, and the male usually came out

of the cavity before commencing this behavior. I

noted other postcopulatory male behaviors (the

slow walk and tail rotation) that have not been

described for the arboreal sciurids. Female postcopulatory grooming of the genitials occurred in

chipmunks and has been described in douglas squirrels by C. C. Smith (1968:38-39).

Farentinos (1972) made the interesting observation that after subordinate male tassel-eared squirrels copulated with the female, they became very

aggressive for short periods of time. During these

periods they initiated many chases and often chased

even the dominant male. A related phenomenon

seems to be found in the eastern chipmunk. Males

that had just copulated with, but lost track of, the

estrus female, had postcopulatory "fits" in which

they ran about, vocalizing loudly in a highly agitated fashion. I do not know if this influenced their

rank positions in the dominance hierarchy, but they

did exhibit an increased tendency to initiate chases

when other males approached them.

The eastern chipmunk appears unique in that

many copulations (minimum of 10 and probably

20 or more) occur during the mating bout, with a

great variety of males. C. C. Smith (1968:61) remarked that copulation only occurred several times

during mating bouts in red and douglas squirrels

and that the dominant male appeared to successfully monopolize the female. Farentinos (1972:319

indicated that as many as eleven copulations occurred during mating bouts in the tassel-eared

squirrel. He also noted that the dominant male was

usually responsible for the first, or first several,

copulations. He did not provide data on the number of different males that copulated with individual females. Farentinos feels that the first copulations are the most likely to result in fertilzation,

hence the dominant males were thought to be the

fathers of most litters. Horwich (1972:66), on the

other hand, emphasized that it was not the dominant male who paired with, and subsequently copulated with, the female in gray squirrels. The matter remains unsettled for the eastern chipmunk,

but it may be possible that the dominant male is

responsible for most of the earlier copulations during the estrus period.

Recent studies on the deermouse, Peromyscus

maniculatus (Birdsall and Nash, 1973), have demonstrated that mixed litters, resulting from sperm

mixing and multiple copulations, are of common

occurrence. Similar studies, utilizing plasma proteins of the young, need to be carried out on the

eastern chipmunk and the arboreal sciurids in

which multiple copulations with a variety of males

has been verified. Until that time, hypotheses concerning the correlation of male dominance with

mating success will remain speculative.

The participation of individual males in many

mating bouts is probably of common occurrence in

the arboreal sciurids. Farentinos (1972) provides

data concerning this subject. He observed a total

of six mating bouts on his study area and many

males participated in more than one chase. A

similar trend occurs in the eastern chipmunk

(Table 16). None of the other studies provide data

on this point.

I could not locate data for the arboreal sciurids

concerning how far males move off their normal

home ranges to participate in mating bouts. It is

obvious, however, in the territorial red and douglas

squirrels that males must move off their own territories in order to breed. In chipmunks, long movements by males of up to 100 meters beyond the

normal ranges were common during breeding season. Data on home range use by the female during

estrus are also lacking in the arboreal sciurid literature, although C. C. Smith (1968:37) mentions that

female red and douglas squirrels spend much of

their time near the periphery of their territories

during estrus. The female chipmunk utilized her
NUMBER 265 67

home range during estrus in a manner similar to

normal utilization, although her average speed of

movement increased. I noted no increased tendency

of the female to use the periphery of her home

range although some female chipmunks made long

distance trips into dense cover off their home range

to lose pursuing males.

The problems of interpretation of data concerning mating bouts of both chipmunks and the arboreal sciurids is obvious. A critical matter is determining if male dominance is correlated with mating

success. This problem can only be answered

through the coordination of field descriptive studies

with laboratory studies on reproductive physiology

and biochemistry. Of great importance is testing

for the existence of mixed letters through blood

protein analysis (Birdsall and Nash, 1973) as well

as determining which copulations during the estrus

period are most likely to result in fertilization.

Only in the case of the douglas and red squirrels

(C. C. Smith, 1968: 37-39) is the dominant male

apparently responsible for all copulations during

the mating bout. Any consideration of evolutionary

transitions from the mating bout type of mating

scheme to the highly polygynous scheme exemplified by the black-tailed prairiedog (King, 1955)

will rest on a resolution of these problems.

Foraging Dynamics in the Chipmunk Population

Habitat Analysis

This study was carried out in the Adirondack

mountains of upstate New York on the east side of

Buck Hill (elevation 658 m or 2157 ft) near the

village of Rainbow Lake in Franklin County. Buck

Hill is almost completely covered with mature hardwood forest dominated by beech (Fagus grandifolia)

and sugar maple (Acer saccharum), except at its

lower elevations where mixed woods consisting of

varying proportions of coniferous and deciduous

species are found (see Braun, 1950:414-422, for a

discussion of Adirondack forest types). The transition from the hardwood forest to the mixed woods

on Buck Hill is abrupt and is correlated with drainage. Hardwood forest occupies the rich soils of the

well-drained slopes, while mixed woods is primarily

found at lower elevations in low, but not boggy,

flats. The flats are composed of soils derived from

glacial outwash. Soils on the slopes are derived

from glacial till (Kudish, 1975:37-38).

My study area was located in the hardwoods

about 46 m above the mixed woods, at an elevation

of approximatly 534 m. The transition zone between the two habitats just below my study site

was abrupt and a well-defined ecotone was present.

The existence of the nearby alternative habitat

(mixed woods) must be kept in mind as it is a

significant factor in the biology of chipmunks on

my study area. In 1973 the study area measured

61.0 X 76.3 m (1.15 acre or 0.465 ha). In 1974, I

enlarged the area to measure 91.5 X 91.5 m (2.06

acre or 0.835 ha). Figure 41 depicts the 1973 and

1974 study areas and shows the location of the

nearby mixed woods and the abrupt ecotone.

The predominant tree species in the hardwood

forest are beech, sugar maple, and yellow birch

(Betula lutea). Red spruce (Picea rubens), red maple

(Acer rubrum), and striped maple (Acer pennsylvanicum) are present in smaller numbers. Occasionally, black cherry (Prunus serotina) or eastern

helmock (Tsuga canadensis) are encountered. In

general, the hardwood forest is relatively free of

undergrowth, except for an abundance of wood

fern (Dryopteris spinulosa).

1974 study area

(2.07 acre)

(034 h3.)

1973 study area

(1.15 acre)

(0A7ha.)

W Hardwoods

Mixed Woods

ecotone

(loo'n)

FIGURE 41.—Study plots for 1973 and 1974, and the location

of the nearby mixed woods and ecotone.
68

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

In the mixed woods are found varying proportions of red spruce, balsam fir, yellow birch, and

red maple. Although beech is occasionally found,

beech and sugar maple are notably absent. Dense

patches of hobblebush (Viburnum alnifolium) are

common. Chipmunks were abundant in the hardwood forest at all times during the study. They

were abundant in the mixed woods only for short

periods of time, especially when the red maple seed

crop was ripe (see "Spring and Summer Foraging

Behavior"). It appeared that the mixed woods could

not support dense populations for long periods.

I gathered data on tree species composition in

the hardwood forest during the fall of 1973 over an

area of 1.61 acres (0.652 hectare). This sampling

area included all of the fall 1973 study area and most

of the 1974 plot (Figure 41). I recorded all trees

over 1.83 m (6 ft) in height, and I measured their

circumferences at chest height (CCH). Since shrubs

were absent and since most saplings were greater

than 1.83 m (6 ft) in height, I omitted very little

woody vegetation from analysis. There were, however, many seedlings of sugar maple and beech

less than ankle high that I did not measure.

An analysis of the frequency distributions of size

classes (based on CCH) for each species provides

a tabular representation of forest structure that is

useful in characterizing the forest (Table 19). Note

that both beech and sugar maple have similar distributions, with an abundance of smaller trees and

a broad distribution of numbers among the larger

size classes. Yellow birch has an abundance of large

trees but it is noticeably lacking in the smaller size

classes.

By direct observation, I estimated that only those

trees with CCH's greater than 0.61 m (2 ft) penetrated into the forest canopy. Table 20 presents

proportions of canopy sized trees for the different

species. Since mature canopy trees are usually the

only trees responsible for seed production, these

proportions are ecologically important measures.

This simplification is applicable to all species except striped maple. Mature striped maple are subcanopy trees. Fortunately, there were only two

mature striped maples on the study site and their

omission is not critical to a treatment of seed production. Beech obviously predominates the canopy

in terms of numbers. Sugar maple and yellow birch

TABLE 19.—Size class distributions of trees by CCH {circumference at chest

height; sampling area = 1.61 acre or 0.652 hectare)

Tto

Q)

-p

<D

•H

t/}

ft

§

o

i

Size classes by CCH

m

0.00-0.15

0.15-0.30

0.30-0.1+6

0.1+6-0.61

0.61-0.76

0.76-0.91

0.91-1.07

1.07-1.22

1.22-1.37

1.37-1.52

1.52-1.68

I.68-I.83

1.83-1.98

1.98-2.13

2.13-2.29

2.29-2.1+1+

2.1+4-2.59

Totals

(ft)

(0.0-0.5)

(0.5-1.0)

(1.0-1.5)

(1.5-2.0)

(2.0-2.5)

(2.5-3.0)

(3-0-3.5)

(3.5-4.0)

(4.0-4.5)

(4.5-5.0)

(5.0-5.5)

(5.5-6.0)

(6.0-6.5)

(6.5-7.0)

(7.0-7.5)

(7.5-8.0)

(8.0-8.5)

.GO0)

(3

I69

80

44

17

7

9

7

9

9

12

7

2

1

_

-

-

-

373

U 0)

S 1-1

co e

290

79

29

6

1

1

_

_

2

2

1

2

4

2

5

1

425

Numbe r

(U 41

_

2

5

7

4

4

4

3

3

2

-

_

_

_

_

_

1

35

d)

0

-d h

5

5

_

3

3

2

_

1

1

_

_

_

_

_

_

_

-

20

of trees

<u

edapl

_

-

-

1

1

1

2

1

_

_

_

_

_

_

_

-

6

P( (D

-H H

W 1

3

19

2

_

_

_

_

_

_

_

_

_

_

_

_

_

-

24

M

8

1

W

_

1

1

_

_

_

_

_

_

_

_

_

_

_

_

_

-

2

X U 0 u <$ <u

H X! S o

_

-

_

_

_

_

_

_

_

1

_

_

_

_

-

1
NUMBER 265 69

TABLE 20.—Species proportions

for canopy sized trees (CCH's

greater than 0.61 m (2 ft);

sampling area = 1.61 acre or

0.652 hectare; N = 116 trees)

Species

Beech

Sugar maple...

Yellow birch..

Red spruce....

Red maple

Black cherry..

Total

Proportion

0.53

0.18

0.18

0.06

0.6k

0.01

1.00

occupy the next position at nearly equal proportions (Table 20).

Species proportions are often misleading because

they ignore the sizes of individual trees. Two areas,

differing radically in tree size and age distributions,

may produce nearly identical species proportions.

For instance, the similar proportions of sugar maple

and yellow birch in Table 20 are misleading because they do not take into account the fact that

sugar maple canopy trees are much larger on the

average than yellow birch canopy trees (Table 19).

To help alleviate this interpretive problem, I estimated the total basal areas of all tree species on

the study plot (Table 21) and the total basal areas

of canopy sized trees of beech, sugar maple, and

yellow birch (Table 22). These totals are potentially useful in comparing the developmental stage

or relative age of the forest in which I worked with

other study areas.

TABLE 21.—Basal area totals (all trees greater

than 1.83 m (6 ft) height measured; sampling

area = 1.61 acre or 0.652 hectare)

Species

Beech

Sugar maple...

Yellow birch..

Red spruce

Red maple

Black cherry..

Striped maple.

Hemlock

Total.

m2/ha ft2/acre

Ik.26

10. lU

3.79

l.oU

O.58

0.32

0.16

0.02

62.0

kk

16

k

2

0.7

0.1

30.31 131.!

373

U25

35

20

6

1

2k

2

886

TABLE 22.—Basal area totals calculated from canopysized trees only (CCH's greater than 0.61 m (2 ft);

sampling area = 1.61 acre or 0.652 hectare)

Species

Beech

Sugar maple... .

Yellow birch.. .

ft2/acre

II.89

8.72

51.7

37.9

15.1

63

21

21

My vegetation analysis allows generalizations to

be made concerning the hardwood forest. Due to

the relatively high total basal area estimate, the

abundance of large trees on the study area, and the

distribution of trees among all size classes in the

dominant species, the forest can be characterized

as a mature and undisturbed growth. There was no

indication of logging activities on the study area

and no signs of fire damage were evident.

Foraging Behavior

AUTUMN FORAGING

CHIPMUNK UTILIZATION OF TREE SEEDS.—Most of

the tree species listed in Table 19 bear seeds that

mature in late summer or fall, producing seeds edible to the chipmunk by late September. Red maple

is an exception in that its fruit ripens and falls to

the ground in June in the Adirondacks (see "Spring

and Summer Foraging"). The seed production

levels of the fall-maturing species are extremely

important variables in the foraging ecology of chipmunks, because chipmunks rely heavily on the seeds

for subsistence during the winter months (see

"Winter Months").

I estimated relative autumn seed production

levels for the various species from 1973-1975 by

visually comparing seed production within each

species through the three seasons. This data is presented in Table 23 with a ranking per species of

negligible, moderate, or abundant seed crop.

The importance of each species as a potential

food source for chipmunks is also dependent upon

its relative abundance in the habitat. Tables 19-22

summarize abundance data, revealing striped maple,

red spruce, and black cherry as minor elements in

the forest. Beech and sugar maple are obviously

dominant species, and yellow birch is subdominant.

An additional variable influencing the adequacy of

tree seeds as a food resource is seed size. Data on
70

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 23.—Autumn seeding success for tree

species on the study area (levels determined by

visual comparisons of seeding during the three

years of study)

Species

Beech

Sugar maple... .

Yellow birch.. .

Striped maple..

Red spruce

Black cherry.. .

1973 197*+ 1975

XX

XX

XX

X

X

- = negligible seed crop; X = moderate

seed crop; XX = abundant seed crop.

seed size is included in Table 28, derived from seeds

recovered from food hoards (see "Dynamics of Burrow-Hoarding").

Because of the small number (2) of mature

striped maples on the study plot (p. 68), the moderate striped maple seed crops of fall 1973 and fall

1974 did not provide a major food source for the

chipmunk population (Table 23). However, some

utilization of the seeds occurred, as evidenced by

the composition of excavated burrow hoards (Table

30). Red spruce, another minor species, produced

moderate cone crops in late summer 1973 and 1974.

I noticed no chipmunk utilization of this food item.

Probably, red squirrels from the nearby mixed

woods (Figure 41) gathered the cones from the

crowns long before they shed their seeds (see "Interspecific Competition for Food Resources").

Yellow birch, a subdominant, produced an abundant seed crop during the fall of 1974 (Table 23).

Although seeds were available in great numbers

on the ground during October 1974, chipmunk

utilization was low (Table 30). Chipmunks probably avoided collecting the yellow birch seeds because of their small size (Table 28). Black cherry

never produced a ripe seed crop during my study

and there was only one canopy-sized tree on my

study plot (Table 19). The tree did, however, drop

unripe seeds one summer that were utilized by

chipmunks (p. 81).

The major food sources during the fall months

of 1973 and 1974 were the seeds of the dominant

species, beech and sugar maple. During fall 1973

a moderate beechnut crop occurred and most foraging by chipmunks was directed toward this item.

During fall 1974, both beech and sugar maple produced abundant seed crops and foraging by the

chipmunk population was directed at both species.

It appeared, however, that the chipmunks preferred

beechnuts to sugar maple seeds. This preference is

probably dependent upon the substantially larger

size of individual beechnuts (Table 28). During

the fall of 1975, seed crop failures occurred in all

species, resulting in the absence of any major food

resource on the study plot. The responses of the

population to this failure are discussed under

"Temporal Availability of Food Resources."

Although chipmunks concentrated their foraging

during the fall months on tree seeds, other items

were also consumed (Table 25). I noted one chipmunk eating a small gilled mushroom (agaric) and

another consuming a land snail. I observed several

chipmunks chewing on the leaves and stems of a

common fern, Dryopteris spinulosa.

FOOD HOARDING METHODS.—Although chipmunks

sometimes immediately consume seeds and nuts

when they find them, most are packed away into

their internal cheek pouches (Figure 42) and transported to other locations for storage. Two hoarding patterns are exhibited by chipmunks: burrowhoarding and scatter-hoarding.

Depositing seeds or nuts in the home burrow

(burrow-hoarding) is the predominant method employed by adults through the fall period. Scatterhoarding, or the deposition of single pouchfulls at

scattered locations under leaf litter (Figure 43), is

rare among adults in the autumn. I observed a

single case of adult scatter-hoarding in October of

1973. In October of 1974, I watched an adult locate and pouch a scatter-hoard, and transport it

into her burrow. It is probable that the adult was

responsible for making the scatter-hoard.

I commonly observed scatter-hoarding among

newly dispersed juveniles during October of 1973

(p. 79), although some of the juveniles also exhibited burrow-hoarding. I recorded one case of

juvenile scatter-hoarding during October of 1974

and commonly watched them burrow-hoard. It is

probable that the development of burrow-hoarding

in juveniles coincides with the acquisition of a

permanent burrow system. If a juvenile hoarded

in a temporary burrow, he would have to transport the hoard when adequate quarters were located. (See "Spring and Summer Foraging Behavior" for further implications of scatter-hoarding.)

CROWN FORAGING VERSUS GROUND FORAGING.—

During September and October of 1973, adult for-
NUMBER 265 71

FIGURE 42.—The eastern chipmunk has internal cheek pouches into which he loads seeds, nuts,

and bulbs for transport to his burrow-hoard.

aging for beechnuts occurred both on the ground

and in the tree crowns in response to the moderate

beechnut crop (Table 23). However, crown foraging was the predominant method of collection.

Although beechnuts were available in the leaf litter

by late September, chipmunks were not filling their

cheek pouches while ground foraging. In contrast,

pouch filling commonly resulted from crown foraging. Adults moved to the ends of uppermost

branches in beech trees in search of hairy burrs

enclosing two or three nuts. The chipmunks severed

the burrs from the branches and removed and

pouched the nuts, which were still enclosed in their

woody seed coat. The empty burrs were dropped

to the ground. Once their cheek pouches were full,

the adults descended to the ground, transported

the nuts to their home burrows, deposited them,

and climbed to the crowns again via the same

routes. I watched this sequence of behavior many

times and it was definitely the major adult method

of obtaining and storing food during the fall of

1973.

In contrast to 1973, I saw no crown foraging at

all by chipmunks during the fall of 1974. Adult
72

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 43.—Chipmunk uncovering a scatter-hoard.

chipmunks foraged exclusively on the abundant

beechnuts and sugar maple seeds (Table 23) that

had fallen from the crowns into the leaf litter.

Beechnuts were pouched with their woody seed

coats intact; the wings of the maple samaras, but

not the membranous seed coats, were removed before pouching. The seeds and nuts were transported into the home burrows for deposition. A

major question arises from these observations:

What factors were responsible for the shift from

crown foraging to ground foraging over the two

fall seasons?

I feel that the shift was related to the different

densities of available food over the two seasons.

In 1973 the beechnut crop was moderate. If the

chipmunks waited for the seeds to fall from the

crowns, the seeds would become buried in the thick

mat of freshly fallen leaves. Chipmunks foraging

on the ground locate seeds primarily by using smell,

much search time being devoted to nosing about in

the leaf litter. It is possible that during years of

moderate to low seed availability (like the fall of

1973), seeds would drop into the leaf litter at such

low densities that search time would become prohibitively high. Under such circumstances, chipmunks can reduce search time by climbing trees

and visually locating seeds on the branch tips. The

drawbacks of tree climbing are (1) the danger involved in climbing (see "Climbing Ability of Chipmunks"), (2) the time invested in climbing. In

1973, the gain accrued from crown foraging outweighed the disadvantages.

During the period of peak beechnut availability

in 1973 (25 September-12 October), the time it

took for chipmunks from different locations on the

study area to fill their pouches while crown foraging remained remarkably constant. I timed a total

of 24 instances of pouch filling in seven individuals

during six observation days from 25 September to

12 October. The mean number of minutes from the

beginning of ascent to the return to the ground

with a full pouch was 5.8 minutes (S.D. ± 1.15).

In these measurements, I timed only those trips

that resulted in full pouches and were not interrupted.

In 1974, I monitored the ground foraging behavior of two adults on my study plot during peak

beechnut and sugar maple seed availability (6-11

October). The average time for a total of 48 uninterrupted trips from leaving the burrow to returning with a full pouch was 4.6 minutes (S.D. ±2.31),

somewhat less than the 1973 measurements, but of

comparable magnitude. Apparent from these measurements is that ground foraging during the autumn of 1974 was efficient enough to rule out the

need for crown foraging. It is doubtful that

the two chipmunks could have reduced their

pouchfilling times by crown foraging because of the

time needed to climb and descend trees. In any

event, the chipmunks obviated the dangers of crown

foraging during 1974 by staying on the ground.

CLIMBING ABILITY OF CHIPMUNKS.—My observations of crown foraging during the autumn of 1973

indicate that chipmunks are not finely adapted for

arboreal maneuvering. I observed a total of four

individuals to fall out of crowns at heights of approximately 18 m. On four other occasions, I heard

the unmistakable thumps of falling chipmunks hitting the ground and I visually located them just

after their falls. None of the chipmunks appeared

seriously injured, but all had landed in the soft

leaf litter.

During the autumn of 1973, the sugar maple seed

crop was negligible (Table 23). Yet the chipmunks

regulary ascended the sugar maple trees, returning to the ground minutes later with full pouches.

Closer observation revealed that the chipmunks

were crossing from the sugar maple crowns into

adjacent beech crowns to forage for beechnuts.

After filling their pouches, the chipmunks crossed
NUMBER 265 73

back into the sugar maple crowns and returned

to the ground via the same route. In several instances, red maple or the single black cherry tree

(Table 19) were used for ascent and descent. Of

special significance is that chipmunks did not regularly climb or descend the beech trees themselves.

The simplest explanation for this behavior is

that chipmunks cannot climb safely on beech

trunks. The bark of mature beech is very smooth.

A chipmunk would find it difficult to climb the

lower portions of the trunk where the trunk diameter is so great that he would essentially be moving

vertically (up or down) on a flat, smooth, surface.

Descending with a full pouch would increase the

danger of falling. Mature sugar maple, on the other

hand, have rough, heavily furrowed bark insuring

an adequate foothold during ascent or during descent with a full pouch. Chipmunks are able to

maneuver in beech crowns, probably because the

higher branches have small diameters that allow

the chipmunks to reach around them for footing.

Also, many of the upper branches are oriented

close to the horizontal, making them easier to climb

than vertical surfaces.

Several observations support my interpretation.

The only beech tree on the study plot that the

chipmunks periodically climbed had a crooked

trunk with unhealthy, cracked bark, and a long

furrow that extended to its lowest limbs. A chipmunk attempted to ascend a large beech tree, but

fell from a height of around 3 m. After making

a second unsuccessful attempt, he abandoned his

efforts. Another chipmunk with a full pouch was

descending from the crown of a large beech tree.

After descending to the lowest crotch in the tree

(about 9 m above the ground) he became noticeably

hesitant in his movements. Finally, he reascended

to the crown, crossed over into a sugar maple crown,

and descended without hesitation.

Although sugar maple trees provide relatively

safe access to beech crowns, some danger is involved.

Crossing between crowns usually included a jump

of around 0.9 m between branch tips. I observed

one chipmunk lose his footing during such a jump,

falling 18 m to the ground. It is probable that

most falls occur in connection with this leap, some

resulting in injury or death.

Although juveniles emerged onto the study area

by mid-September of 1973 (see Table 10), they did

not begin climbing trees until early October. Prior

to that time they foraged without much success in

the leaf litter. This indicates that chipmunks do

not have a strong disposition to climb trees in

search of food. Probably, the juveniles learned the

whereabouts of the food resource by observing tree

climbing in neighboring adults. I observed no indication of mothers teaching their young to climb

trees during the predispersal phase. When the juveniles first began to climb, they often spent long

periods (up to 20 minutes) in the crowns before

returning to the ground with empty pouches. Although tree leaves blocked my observation of their

activities, I assume they were consuming, but not

pouching, food.

TEMPORAL AVAILABILITY OF FOOD RESOURCES.—

During the fall of 1973, beechnuts were available

for collection for approximately one month, from

mid-September to mid-October. By 12 October,

the resource was apparently depleted, as evidenced

by the disappearance of adults into their dens. I

observed no adults on the study area after 12 October. I verified the near depletion of beechnuts by

scanning beech crowns with a spotting scope. Nearly

all burrs were open and empty. I also searched the

leaf litter for nuts and uncovered few. Some juveniles remained active after the adults disappeared,

two being observed above-ground during my last

observation sequence on 24 October. Figure 44

shows the decline in activity for October 1973.

During the autumn of 1974, beechnuts and sugar

maple seeds were available in abundance on the

ground and in the crowns from 18 September

through 18 October. On 19 October the crowns

of both sugar maple and beech still had seeds,

although most had fallen to the ground. The seeds

and nuts were still common in the leaf litter compared to their rarity in the leaf litter at the same

time during the previous year. Adults and juveniles

alike were still active on 19 October, the date of my

last observation sequence (p. 16). Figure 44 graphs

activity levels through October of 1974, demonstrating high levels through the termination of my study.

I was later informed by residents of the Adirondacks that chipmunks were preoccupied with foraging in hardwood forests until mid-November or

later. These observations are in sharp contrast with

the situation in 1973, when the crop was deplete

by mid-October and most chipmunks were entering

into hibernation.
74

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

25

SI

z

Si

 15

1974

10 15

DATE - DAYS IN OCTOBER

FIGURE 44.—Activity levels for October 1973 and 1974. Ordinate value derived

from the standard observation sequences denned on pp. 2-5. Note that activity

declined gradually through October during 1973 but maintained high levels

during 1974 (T = termination date of autumn study for the year).

During the fall of 1975, no major food resources

were available to the chipmunks (Table 23). Aboveground activity on the study area was low, most

chipmunks retiring to their burrows by late September. The seed failure seemed to be Adirondackwide, chipmunk activity during October being oriented only towards artificial food sources provided

by Adirondack residents.

ESTIMATED WINTER HOARD SIZES FOR 1974.—I

estimated the number of beechnuts comprising a

full pouch by uncovering a beechnut scatter-hoard

made by an unmarked adult female living off my

study plot. She buried 34 beechnuts from a single

load. Similarly, Allen (1938:78) found 32 beechnuts

in the full pouches of a trapped chipmunk. It is

reasonable to assume that both cheek pouches of

adults can hold comfortably a total of 25 beechnuts.

During the fall of 1974, I gathered data allowing

for a crude estimate of potential food hoard size.

I monitored foraging behavior of two adults during early October. One adult transported an estimated 25 pouchfulls of beechnuts into her burrow

over a 3-hour interval on 6 October. On 8 October, another adult transported an estimated 22

pouchfulls during a 3-hour interval. Assuming a

minimum of 25 beechnuts per pouchfull, the first

individual stored 635 beechnuts and the second

stored 550 during the 3-hour interval. Based on this

data, it is safe to assume that the chipmunks could

easily have stored a thousand nuts per day. If nuts

were available in quantity for a week, stores of

around 7000 nuts could be built with ease. My

data on food availability for the autumn of 1974

indicate that nuts were available in abundance for

a minimum of a month, and were foraged upon

for one and a half to two months. Taking into account this long availability, hoard sizes approaching

15,000 to 20,000 are easily conceivable.

SPATIAL AVAILABILITY OF FOOD RESOURCES.—Since

beechnuts and sugar maple seeds comprised the

major autumn food resources, maps of the crown

distributions for canopy-sized, seed-producing trees

reveal critical aspects of food spatial availability

patterns (Figures 45, 46).

During 1973, chipmunks foraged almost exclusively on beechnuts. Figure 45 reveals that individual chipmunks residing anywhere on the study

plot would have access to a minimum of 13—15

beech trees if movements were restricted to within

24.4 m of the home burrow. Movements usually
NUMBER 265 75

(50 n

1

FIGURE 45.—Crown-shadows of canopy-sized beech trees on

2.41 acre (0.98 ha) study plot (this plot includes all of the

1974 study plot depicted in Figure 41, plus 15 m (50') to

the west; dotted lines included for trees whose trunks were

off the plot, but whose crowns intersected the plot).

FIGURE 46.—Crown shadows of canopy-sized sugar maple

trees on 2.41 acre study plot (see legend on Figure 45).

Dotted lines included for trees whose trunks were off the

plot, but whose crowns intersected the plot.

ranged beyond 24.4 m Figure 12 and p. 19), making a minimum of 20-30 trees available on most

chipmunk home ranges.

Since foraging in the crowns required sugar

maple access routes, the spatial distribution of canopy-sized sugar maple trees is also instructive (Figure 46). Even if individuals restricted their movements to within 24.4 m of their burrows, a minimum of 4 or 5 sugar maple trees would be accessible. Since movements normally ranged beyond 24.4

m, most home ranges included ten or more trees.

Superimposing Figure 45 onto Figure 46, I calculated that at least 90% of the sugar maple crowns

overlap with adjacent beech crowns. Remembering

that chipmunks move readily from crown to crown

once access is obtained, it becomes evident that

nearly all canopy-sized beech trees on their home

ranges were accessible for crown foraging.

Individual canopy-sized beech trees varied in productivity levels, although all mature trees produced

visibly moderate nut crops. Large sample sizes tend

to buffer the effects of variability. Since individual

chipmunks had access to at least 20-30 nut producing beech trees within their normal ranges, I

feel that sampling areas were large enough to approximate the average productivity levels of the

hardwood forest and to include at least several

high-productivity trees. This obviated the need

for long excursions out of the normal ranges (Figure 12) during the 1973 autumn season. Stated

differently, I conclude that chipmunks experienced

no added payoff in terms of food resource location as a result of excursions 30 m or more from

their home burrows.

During the autumn of 1974, beechnuts and sugar

maple seeds were available in abundance on the

ground (Table 23), all canopy-sized trees producing

high levels of seeds. Beechnuts tend to fall straight

down, making the crown diagram (Figure 45) a

good approximation of nut availability. Sugar

maple samaras are wind dispersed, tending to make

their availability pattern more homogeneous than

is indicated by the crown diagram (Figure 46).

Taking into account the high production levels

and seed dispersal patterns of both species, I conclude that the spatial patterning of the seed and

nut resource was maximally homogeneous during

the fall of 1974. Using the same argument presented

for the autumn of 1973, I further conclude that

chipmunks had little need to make long excursions
76

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

out of their normal home range confines (as indicated in Figure 12) in search of concentrations of

food resources.

The foregoing conclusions only apply to the peak

period of food availability. During late September

of 1974, most foraging was taking place under

scattered beech trees that were shedding nuts before most other trees. For several days, these trees

produced scattered and concentrated resource

patches that induced long movements approaching

60 m by some individuals on my study plot. The

long movements stopped after two or three days

when nuts began falling throughout the forest.

During the autumn of 1975, a failure of seed

and nut production occurred throughout the study

area and the surrounding forest (Table 23). Lacking available food even at long distances from

their burrows, most chipmunks disappeared from

above-ground by late September.

JUVENILE FOOD BEGGING.—I gathered no evidence

indicating that newly emerged juveniles are taught

to forage by their mother. However, the observation

described on page 42 offers evidence that provisioning of natural food items by the mother might

occur. The surrender of pouched food items to the

young may commonly occur in the natal burrow

preceding emergence. Although it would not enlighten the young about foraging techniques, such

behavior would allow youngsters to taste appropriate food items before weaning.

WINTER MONTHS

I made no detailed investigation of hibernation

and winter behavior in the Adirondack chipmunks;

however, I did perform a laboratory study of feeding behavior in an artificial environment that simulated winter conditions (see p. 89).

The eastern chipmunk does not put on large

deposits of subcutaneous fat prior to hibernation

(Panuska, 1959). His primary source of energy during hiberation is his burrow-hoarded food. Studies

by other investigators have shown that the chipmunk may enter torpid states accompanied by low

metabolic rates during the winter months (Wang

and Hudson, 1971; Panuska, 1959). Torpidity is

cyclic, however, with torpid periods rarely continuing beyond three or four days. It is probable that

chipmunks experiencing torpid states undergo

arousal every several days to consume portions

of their food hoard. Some individuals cannot be

induced to torpidity; further, the degree of torpidity

varies considerably between chipmunks (Panuska,

1959). The intensity of torpor may be related to

latitude, with individuals from colder regions at

high latitudes entering torpidity with greater regularity (see "Food Storage and Energetics").

Although the Adirondack chipmunk spends most

of his winter underground, he may emerge during

warm periods to forage on seeds and nuts still hidden in the leaf litter. Adirondack residents living

near my study area have reported short spurts of

foraging activity during the winter months, usually

during periods of snowmelt. In several cases, they

observed chipmunks to burrow up through 0.5-

1.0 m of snow during late winter. It is possible that

this latter activity is correlated with early breeding

behavior in the species. The final spring emergence

of adult chipmunks in the Adirondacks usually

occurs in early May, in response to the disappearance of snow and the advent of warm weather.

SPRING AND SUMMER FORAGING

I designate the spring and summer foraging period as lasting from the emergence of chipmunks

in late April or May until late July. I gathered

detailed notes on foraging during this period in

1974 and 1975, and I gathered supplementary notes

in 1973 and 1976.

EMERGENCE FROM HIBERNATION.—Chipmunks

emerged from hibernation in response to weather

factors at different times during each year of study.

In 1974, I spotted the first chipmunk on my study

area on 28 April, after monitoring the area since

mid-April. I noted spurts of activity through the first

two weeks of May, but intermittent cold spells and

shallow snow depressed activity on certain days.

Activity was consistently high after 14 May. In

1975, I arrived on the study plot on 1 May. I noted

much activity by 3 May, and activity levels were

consistently high thereafter in response to continually mild weather and the disappearance of snow.

In 1976, mid-April was marked by an unusually

warm spell and the absence of snow. I was told by

Adirondack residents that chipmunks were very

active during this period. I noted much activity

upon my arrival during the first week of May. Then
NUMBER 265 77

cold weather set in that depressed activity. Heavy

snowfall on 19 May lasted several days. Activity

levels finally rose as warm weather returned in

late May.

FORAGING ON OVERWINTERED SEEDS AND SPROUTS.—

During May of 1974, few overwintered beechnuts

were available in the leaf litter. This reflects the

moderate beechnut crop of the previous fall and

the efficiency with which chipmunks utilized the

available nuts at that time (Table 23; "Autumn

Foraging"). Scattered nuts that escaped predation

germinated into small seedlings during May. Chipmunks consumed the entire seedling when they

encountered one.

During the spring of 1975, beechnuts and sugar

maple seeds were abundant in the leaf litter, reflecting the successful seed crops of the previous fall

and the inability of the chipmunks to utilize all

of them at that time. During the first two weeks

of May, chipmunks from all parts of my study area

were actively pouching and burrow-hoarding these

items.

Chipmunks collecting overwintered seeds are

tapping a temporally unstable resource. As temperatures rise the seeds are bathed in warm waters

from spring rains and the seeds germinate. The

value of the seed and nut resource to the chipmunks

changes radically during this process. Before germination, seeds and nuts are compact, storable energy

packets. Once germinating, nutritional content

rapidly decreases as the seeds utilize stored energy

reserves for growth. Soon the seeds become soft and

swollen with water, making storage in the burrow

unreasonable. Eventually unfolding leaves, the stems

and roots of the seedlings become woody, the resource now being almost useless to the chipmunks.

By 15 May, seeds were rapidly germinating and

seedlings of both species carpeted the forest floor.

Chipmunks relished the succulent seedlings of

beech, consuming them rapidly whenever encountered. Chipmunks never hoarded seedlings. By 25

May, most seedlings were becoming woody and

chipmunk utilization was low. That an abundance

of seeds escaped predation indicates the inability

of the chipmunks to utilize a large percentage of

the abundant seed crops of fall 1974. This can be

contrasted to the spring of 1974, when seedlings

were rare after the moderate beechnut crop of fall

1973 (see Table 23).

TROUT LILY BULB UTILIZATION.—Trout lilies

(Erythronium americanum) were very abundant on

all parts of my study plot and their bulbs were an

important food item from late May through July

during all years of my study (1973-1976). Small

shoots usually appear by late April, but leafing

and flowering do not occur until mid or late May.

Shoots rise from small spherical bulbs with diameters up to around 13 mm. The bulbs are sweet to

the taste. Chipmunks located them by digging down

at the base of emergent leaves and uncovering the

bulbs at 2.5-5.0 cm depth. Small rootlets emerging

from the bulbs were snipped off with the incisors

before the bulbs were eaten or pouched. Utilization

from late May through July during each year was

evidenced by an abundance of excavations visible

on the forest floor.

On 10 June 1974, I followed an adult and monitored her foraging behavior continuously for 7.75

hours. Nearly all her foraging behavior during this

interval was directed towards the excavation of

bulbs. She excavated an approximate total of 124

bulbs, consuming 22 of them on the spot and hoarding the other 102 bulbs. It is obvious from this

data that individual chipmunks can build substantial hoards of bulbs. The uncovering of a burrowhoard in mid-June revealed such stores (see "Burrow-Hoarding Dynamics" and Table 29).

Although trout lily bulbs were superabundant in

the hardwoods, most plants did not flower and

fruits were never in abundance. This led me to

question how the species survived the high incidence of predation by chipmunks. By excavating

trout lily bulbs through June and July, I found

that most reproduction occurs vegetatively. After

the leaves wilt away in mid-June, the bulbs send

out one to three lateral shoots that extend up to

about 0.4 m. The shoots concentrate tissue at their

tips, gradually transforming into new bulbs. In

July, the connecting lateral shoots disintegrate. The

new bulbs lie hidden until the following spring,

when they produce emergent leaves. This mode

of reproduction gives the species a high reproductive potential. It appeared that chipmunk predation

on the study area did not drastically alter their

numbers.

Other wildflower species in the hardwoods produce edible bulbs. These species are not abundant

like the trout lily and were never directly observed
78

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

to be excavated on the study area. However, bulbs

of these species were periodically utilized by chipmunks, as evidenced by their inclusion in an early

summer burrow-hoard (Table 30).

LONG MOVEMENTS FOR RED MAPLE SEEDS.—Red

maple is a common species in the mixed woods

near the study plot (see "Habitat Analysis") and

several trees are found in the hardwood stand

(Table 19). Red maple flowers in late April or early

May, the seeds ripening and falling to the ground

in late June. During 1973 and 1975, the red maple

seed crop was abundant. Chipmunks on my study

area readily pouched and hoarded the seeds by foraging under the scattered trees in the hardwoods

and by making excursions into the nearby mixed

woods (Figure 41). Although I did not quantify

recruitment into the mixed woods, I made the general observation that chipmunks were exceedingly

common there through late June and early July of

the two years. At other times during the year, the

chipmunk population in the mixed woods was

sparse. Few individuals overwintered there.

The red maple seed crop of 1974 was almost

negligible, probably in response to heavy frosts during the first week of May, which coincided with

flowering in the species. Scattered trees did, however, produce significant seed crops.

On 19 June 1974 I followed an adult female

(9 30), who lived near the center of my study area.

After an hour of normal movements, she made a

long and directed movement to a point 33 m beyond the southeast corner of my study grid. There

she began foraging under a single red maple that

had an abundant seed crop. After 30 minutes of

foraging, she returned to her normal range with a

full pouch, deposited the seeds in a hollow log,

and returned to the red maple to forage.

I subsequently found other individuals utilizing

the site. Figure 47 depicts a map of the study area,

the site of the red maple tree, and the marked animals I noted utilizing the site on a regular basis

from 19 through 30 June. As one can see, long

movements by both sexes to the red maple site occurred, the longest being 158 m for c?16. (For

comparison with normal movements see Figure 6).

A major point is that movements to the red maple

site were often well beyond the normal home range

confines measured for specific individuals earlier in

the season. The extreme patchiness of the red maple

FIGURE 47.—Recruitment of individuals to a single red maple

tree that produced abundant seeds during the summer of

1974. Circles identify individual chipmunks that commonly

foraged under the red maple tree. The circles are placed at

their home burrow locations. Distances between the home

burrows and the red maple site are indicated for each

individual.

resource required deviations from the normal spacing system. My observations did indicate, however,

that each individual was still spending much time

in his normal home range area, mostly foraging for

trout lily bulbs. Relatively fast and directed movements to the red maple occurred between bouts of

trout lily foraging. The maple seeds were depleted

by the first week of July and the chipmunks thereafter remained in their normal ranges.

The problem of how and why individual chipmunks located the red maple tree at such great

distances from their burrows remains unsolved.

Trout lily bulbs were still available in abundance

in the hardwoods during late June, although their

external leaves had wilted away; however, chipmunks demonstrated heavy utilization of the bulbs

as late as mid-July. Therefore, the absence of food

resources on the normal range cannot be used as an

explanation for the initiation of long movements.

Big movements may periodically occur in spite of

food availability near the burrow, since there is a

high premium on the location of highly concentrated, preferred food items. However, I doubt that

periodic, random long movements would suffice to

bring so many individuals to such a small site. I

was unable to gather any evidence that individuals

learned the whereabouts of the site by watching

and following neighbors, although this is a feasible

explanation.
NUMBER 265 79

During the period from mid-June to mid-July of

1974, long distance movements by males were common for reasons other than foraging. I noted females in estrus on my study site from 4 to 12 July

(see "Mating Behavior"). Investigative excursions

by males into the home ranges of females were

common as early as 20 June. Interestingly, I noted

no male investigative approaches at the red maple

site, although both sexes utilized the site during

late June.

I observed ^16 several times filling his pouch

at the red maple site without showing any attention to nearby females. Yet, he often approached

females as he crossed their ranges while transporting food back to his home range or while moving

from his burrow to the red maple site. Another

male made many long excursions in late June and

was involved in many interactions with females.

Several times he passed near the red maple site and

I noted that he approached females in that area.

However, I never saw him utilizing the red maple

site for foraging.

I feel that long distance movements by males

during late June can be attributed to two possible

motivations, one being related to securing food

resources, the other to the location of estrus females.

Lack of interactions of a sexual nature under the

red maple tree indicates that the two motivational

states are not compatible. An interesting observation lends credence to this interpretation: when

females came into estrus, none of the males that

congregated on their home ranges spent any time

foraging.

SCATTER-HOARDING BEHAVIOR.—During May and

early June of 1974 and 1975, I attempted to locate

the home burrows of all chipmunks on the study

plot by chasing individuals into cavities and placing small piles of sunflower seeds at the entrances.

Usually, individual chipmunks emerged after several minutes, located and pouched the seeds, and

subsequently transported them to the home burrow

(thereby revealing the burrow location).

By early June of both years, this method of burrow location usually proved unsuccessful. Most

adult chipmunks persistently scatter-hoarded the

sunflower seeds in the leaf litter, rather than taking them directly into their burrows. To check if

scatter-hoarding was being induced by sunflower

seeds only, I baited with beechnuts I had collected

the previous fall. Most chipmunks scatter-hoarded

the beechnuts. Proof that scatter-hoarding regularly occurs in response to natural food items came

during June and early July when I observed adult

chipmunks commonly scatter-hoarding trout lily

bulbs and red maple seeds.

This predominance of scatter-hoarding among

adults during the summer is strikingly different

from the hoarding behavior of adults during the

fall. During the autumns of 1973 and 1974, adults

burrow-hoarded almost exclusively. Scatter-hoarding

was rare, although I noted it among newly dispersed

juveniles during 1973 (see "Autumn Foraging").

It is my observation that most scatter-hoards are

temporary and are later transported into the home

burrow by the chipmunk that made them. On 10

June 1974, I followed an adult female continuously

for 7.75 hours. During that interval I watched her

locate six scatter-hoards of trout lily bulbs and

transport each into her home burrow. In one instance, she went successively in a directed fashion

to three separate scatter-hoards, stuffing her pouches

and transporting the bulbs into her burrow. The

absence of investigative behavior (nosing around

the leaves) indicated that she was aware of the

precise locations of the hoards.

On 13 July 1974, I watched an adult locate three

different scatter-hoards of bulbs and transport

them into his burrow. In one of these instances,

he made a directed movement to, and transported

into his burrow, a scatter-hoard he had laid down

only one hour earlier. In early May 1975 I observed an adult female scatter-hoard a load of overwintered beechnuts she had gathered from the leaf

litter. Six hours later, she made a directed movement to the precise spot of the scatter-hoard and

transported it into her burrow.

Table 24 lists the approximate longevities of 16

scatter-hoards that I monitored. I carefully checked

each hoard at least once a day from the time I

observed it to be made. I induced some of the scatter-hoards by baiting with sunflower seeds. The

data indicate that many scatter-hoards have a short

duration, disappearing within hours, or at least

within a day or two, of the time they made. Others

escape transport. One scatter-hoard lasted six days.

Two lasted at least 12 days (at which time I left

the study area for a month) and another lasted at

least 22 days. The latter scatter-hoard consisted of

red maple seeds. After 15 days the seeds had

sprouted into small seedlings and the hoard was
80

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 24.—Maximum longevity of scatter -

hoards

Type of

scatter-hoard

Trout lily bulbs

Trout lily bulbs

Sunflower seeds

Sunflower seeds

Sunflower seeds

Sunflower seeds

Sunflower seeds

Sunflower seeds

Sunflower seeds

Red maple seeds

Red maple seeds

Red maple seeds

Trout lily bulbs

Red maple seeds

Red maple seeds

Red maple seeds

Maximum

longevity

1 hour

6 hours

2.5 hours

2.5 hours

2.5 hours

1 day

1 day

1 day

1 day

2 days

2 days

2 days

6 days

12 days or more

12 days or more

22 days or more

probably of little use to the chipmunks. It is probable that germination results if any seeds are left

scatter-hoarded in the moist leaf litter for longer

than two weeks.

I observed no clear-cut patterns concerning where

scatter-hoards were made. Some were within 3 m

of the home burrow, others were 18-24 m from

the burrow, close to the normal home range periphery. In addition, I observed red maple seed scatter-hoards to be made by chipmunks near the red

maple site during June of 1974 (see p. 78) up to

100 meters from home burrows and well out of

normal ranges.

OTHER FOOD ITEMS.—Chipmunks periodically consume perishable items that are not fit for longterm storage in the burrow-hoard. It is my impression that such perishable items do not constitute

much bulk in the chipmunks diet; therefore, they

are best viewed as supplemental food types. Their

importance in the diet, however, should not be

underestimated. It is possible that these items provide vitamins or minerals necessary for healthy

existence.

Table 25 summarizes my observations on consumption of perishable items. I observed each of

the items to be consumed on two or more occasions unless otherwise indicated. I saw only several

instances of earthworm and insect predation; however, it is possible that chipmunks commonly consume such invertebrates while investigating hollows inside trees and stumps or in the ground.

An observation of bird brain consumption warrants detailed description. During late June of 1974,

I watched an adult chipmunk locate a winter wren

(Troglodytes troglodytes) nest among the roots of

a large fallen tree. The nest contained two chicks.

The chipmunk removed both chicks, broke open

their skulls, and consumed their brains. She left the

bodies of the chicks laying on the ground uneaten.

I observed no other predation of bird chicks during

my study.

TABLE 25.—List of food items utilized by chipmunks on the Adirondack

study plot

Hoarded food items

Major

Beechnuts

Sugar maple seeds

Trout lily bulbs

Red maple seeds

Minor

Yellow birch seeds

Striped maple seeds

Black cherry seeds

Bulbs of miscellaneous

wildflowers

Miscellaneous small

seeds

Perishable food items

Agaric mushrooms

False truffles

(underground puffballs)

Fungus on rotten leaves

Wood fern (chewing on

leaves and stems)

Beech and sugar maple seedlings

Sugar maple flowers

Trillium flowers and fruits

Newly unfolding leaves of beech

and sugar maple samplings

Oxalis leaves (based on single

observation)

Insects (larvae, pupae, adults)

Earthworms

Bird brains (based on single

observation)
NUMBER 265 81

In addition to excavating wildflower bulbs, chipmunks sometimes excavate small underground puffballs (false truffles) during the summer months.

The truffles are spherical, with diameters seldom

exceeding 2.5 cm. They were found 7.5-12.5 cm

below the leaf litter in rich soil along a small

temporary stream that crossed my study plot. The

chipmunks never hoarded this item; they consumed

the dark brown hyphae enclosed inside the leathery

covering.

The single mature black cherry tree on my study

site (Table 19) produced abundant berries in

1974. Most of the berries, still green and unripe,

began falling in early July in response to insect

larval infestation of their outer flesh. I observed

some utilization of the berries; chipmunks whose

ranges overlapped the tree commonly carried pouchfulls into their burrows. During some years, this

may produce a significant autumn seed crop.

SPATIAL AVAILABILITY OF FOOD RESOURCES.—I did

not map the distributions of spring and summer

food resources, but several points were obvious to

me. First, the spatial availability of overwintered

beechnuts and sugar maple seeds (and seedlings)

approximated their spatial availability in the leaf

litter during the previous fall (see "Autumn Foraging"). Seeds were available throughout the study

plot and chipmunks apparently were not forced

to move out of their normal ranges (Figure 12) in

order to intercept them. The trout lily bulb resource was superabundant and very homogeneous

on the study plot. Although some variation in density was apparent, trout lilies were available everywhere on the plot and foraging by chipmunks did

not drastically reduce their numbers. The red

maple seed crop was also homogeneously distributed

during years of successful seeding, but only in the

mixed forest near the study plot. Few red maple

trees were on the study area (Table 19). The presence of seeds in the mixed forest induced chipmunks to move off their normal ranges to forage

in the mixed woods when seeds were available.

BURROW PILFERING.—I noted three instances during my study of individuals removing hoarded food

items from other chipmunk's burrows. The first

two instances of pilfering occurred in response to

the disappearance of a neighbor. During early May

1974, 9 22 robbed 9 10's former home burrow of

beechnuts, a week after 9 10 had moved to a new

burrow system nearby (see p. 40). In early May

1975, I watched o"6 remove eight pouchfulls of

beechnuts from a burrow around 15 m from his

home burrow. A week prior to this incident, I had

observed an unmarked chipmunk utilizing the burrow. Probably, the unmarked individual met his

end, because I never observed him in the vicinity

of the burrow thereafter.

The most interesting case of burrow pilfering

occurred on 4 July 1974, when 9^0 was in estrus

(p. 40). While she was involved with males near

her home range periphery, a neighboring female

(9 48) intruded into her burrow and made off with

four pouchfulls of beechnuts. This was my only

observation of the pilfering of an inhabited burrow.

The resident did not distinguish the intruder from

her male suitors. At any other time, 9^8 probably

could not have approached the burrow without

drawing 9 30's attention.

LATE SUMMER INACTIVITY

It is significant that above-ground activity levels

were low from late July until early September during all three years (1973-1975) of study. Many investigators have noted the late summer lull in

activity (Yerger, 1955; Seton, 1929:210-211; Schooley, 1934; Allen, 1938:73), and several explanations

have been expounded. Wolfe (1966) felt high temperatures and summer breeding (particularly gestation and lactation in females) to be two likely

causes. Dunford (1972) reviewed this problem, refuting the high temperature hypothesis and pointing to the inadequacies of the summer breeding

hypothesis. He concluded that the causative factors

of the late summer lull remain a mystery, but suggested that food supply might be a critical factor.

My observations of the Adirondack population tend

to support a food supply hypothesis, but also point

to the importance of other factors.

DWINDLING FOOD SUPPLY.—During years of successful red maple seeding, the seed supply is depleted by early or mid-July. Seeds and nuts of sugar

maple and beech may be available during August

in the tree crowns, but these resources are not ripe

for consumption or collection until mid-September.

Trout lily bulbs are available in late summer, but

their external leaves are wilted away and they must

be located by smell alone. It is also possible that

biochemical changes in the constitution of the bulbs
82

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

render them a poor food source during late summer

and fall.

Late summer, therefore, is earmarked by low food

availability in the Adirondacks, no major food

sources being available above ground (Figure 51).

However, late spring and early summer hoarding

behavior directed towards (1) overwintered beechnuts and sugar maple seeds, (2) trout lily bulbs,

and (3) red maple seeds has resulted in underground food stores that the chipmunk can rely on

until September. It is probable that during late

summer food scarcity, burrow-hoarded food is of

critical importance. The lack of concentrated

sources of food above ground probably results in

lowered activity levels from late July until midSeptember. Another factor, however, may also influence the activity of chipmunks during this time

period.

BOTFLY INFECTIONS.—In some areas, chipmunks

are heavily infested by the larval stages of the botfly, Cuterebra emasculator (Merriam, cited in Seton,

1929:198; Mearns, 1899:352). The larvae burrow

under the skin, usually in the lower abdominal

region. Fifty percent of the animals captured in

the study area during mid-September of 1974

showed botfly infection (Table 26). Note that

newly emerged juveniles, like adults, had a high

incidence of infection.

TABLE 26.—Botfly infestation levels in animals captured from

10-25 September 1974

Age group

Adults

Juveniles..

0

10

16

No. of

per

1

8

10

infections

individual

2 3

2

h l

k

-

l

Total %

infected

50

50

Recent studies by Bennett (1955, 1972, 1973)

have delineated the effects of the botfly parasite on

chipmunks. During development, the larvae apparently have little effect on the activity of chipmunks,

although parasitized animals are often highly

anemic. However, after the larvae leaves its host,

lesions become purulent (puss-filled) and activity is

severely reduced. Chipmunks with one to three

larvae are usually not permanently damaged, but

heavily infected animals (9-14 larvae) may die of

post-emergence infection. Bennett felt that purulent lesions are normal in the natural situation,

and populations should show some reduction of

activity during the period of infestation. Bennett

demonstrated that the parasitic larval stage only

occurs during late summer or early fall, from late

July through September. Therefore, I feel the reduction in above-ground activity during late summer in the Adirondacks could be related to botfly

infestation. First, chipmunks may become inactive

in response to actual parasitization or to secondary

infection after the larva leaves. Second, the reduction in their movements may decrease the incidence

of infection.

Bennett (1972) studied the life history of the

parasite, but never observed the method of host

infection or general oviposition behavior. Eggs may

be laid above ground, at the entrances to cavities

or tunnels. Adult chipmunks may brush against

them during their daily explorations. Some flies

may penetrate directly into the burrows to lay eggs

(C. emasculator is host specific to Tamias striatus).

This would explain the presence of developed

larvae in juveniles that have just left their burrows

for the first time.

Base on the evidence I have presented, I feel

that the late summer lull in activity is best explained by a combination of two factors: (1) low

food availability above ground, and (2) botfly infestation.

DYNAMICS OF BURROW-HOARDING

The adaptive value of burrow-hoarded food during the winter months is obvious. Since chipmunks

do not put on fat reserves prior to hibernation

(Panuska, 1959), they must rely on hoarded food

for energy during the hibernation period. However,

the high incidence of burrow-hoarding behavior

that I observed during the spring and summer indicates that hoards may likewise be critical for the

summer or late summer period. To learn more

about the dynamics of hoarding behavior, I excavated burrow systems of chipmunks living slightly

off the study plot during the springs of 1974 and

1975. Students and faculty involved in the ecology

program at nearby Paul Smiths College provided

manpower for the excavations.

I located home burrows by chasing chipmunks

into small cavities and leaving piles of sunflower
NUMBER 265 83

seeds at the entrances. Upon discovery of a pile,

individual chipmunks usually pouched the seeds

and transporated them into their burrows. This

method revealed the whereabouts of the chipmunk's

major burrow system, the site of his nest and his

burrow-hoarded food.

STRUCTURE OF BURROWS.—Figures 48-50 diagram

the major aspects of burrow structure in three

burrows that I excavated. In addition, I excavated

three other burrows that I have not pictured. Burrows varied in complexity, but share many attributes. The following general description is derived

from the six excavations.

Burrows usually possess a single entrance that

is used by the resident chipmunk, although one

that I excavated (Figure 49) had two entrances in

close proximity that led to a common tunnel. Some

burrows have alternate entrances that the resident

chipmunk keeps plugged (Figure 48) with leaves

or soil. On the study plot I commonly observed a

shift in entrance location from fall to spring, although individual chipmunks were obviously still

living in the same burrow systems. Several times,

I saw chipmunks stopping up old entrances with

leaves as they shifted their use to a new entrance

nearby.

The entrance leads into a tunnel (around 3.75

cm diameter) of variable length (3-4.5 m in Figures

48-50) that opens into the main burrow system.

The long entrance tunnels may penetrate down

into the soil or may run horizontally into hillsides

or into mounds produced by stumps of large fallen

trees. The depth of the main system ranged from

about 0.5 to 1.0 m, lying just above hardpan in

glacial till soil.

The main system is a complex network of interlacing, anastomosing tunnels of variable diameter.

It is probable that many burrow systems were originally constructed among the root systems of large,

dead trees; as the roots rotted away, a natural system of tunnels was provided.

The nest cavity is centrally located in the burrow

system, with three to five passageways leading into

surrounding galleries. The cavity is spherical with

a diameter of 15-25 cm and is filled with crushed

leaves used as nesting material. The nest is surrounded by many elongate cavities, or galleries,

that are interconnected by smaller tunnels. The

galleries are the storage sites of most hoarded food

and may be 0.3-0.6 m in length, with diameters up

to around 12.5 cm. Tunnels and galleries alike

often possess small dead-end pockets, filled with

hoarded food or woody husks and seed coats left

over from consumed food. I found no defecatoria

in the tunnels I excavated.

Burrows also contain deep, tapered passageways

leading down into hardpan. In several cases, the

diameters of these passageways decreased such that

a chipmunk could not fit. This indicates that the

passages had their origins as root-tunnels. One such

passage was filled with water at hardpan level. It is

possible that deep tunnels act as drains, preventing

flooding of burrow systems during heavy rains or

spring thaws.

The striking complexity of burrow systems offers

further evidence for the traditional nature of burrows on the study plot. As I stated previously, I

never saw signs of large scale diggings that indicated complete burrow systems were being constructed. The energy required for such a project

would be prohibitive. Suitable sites in the habitat

probably already have burrows, and chipmunks dispersing into new areas face the major problems of

locating them and assessing their suitability for

permanent habitation.

FOOD HOARDS.—Stored food is located at several

major positions in the burrow systems. Most is

found in elongated galleries, usually those closest

to the nest cavity. Smaller hoards are stashed in

small side pockets throughout the burrow. Substantial amounts of food items are deposited in the

nesting material, a single concentrated hoard often

occurring at the bottom of the nest cavity. The

positions of major and minor hoards in the three

excavated burrows are indicated in Figures 48-50.

The numbers of food items recovered from burrows varied considerably from year to year from

burrow to burrow. Table 29 tallies the hoard composition of three burrows I excavated in early summer of 1974. Remember that the fall of 1973 was

earmarked by a moderate beechnut crop and by a

crop failure in sugar maple (Table 23). Note that

all three burrows contained beechnuts in early

June, two with substantial amounts of 1290 and

2700 (Table 29). This indicates that reasonably

large hoards of beechnuts remained available for

summer use after the winter period of hoard utilization. Two of the burrows had trout lily bulb

hoards, a sign of spring foraging. The 1974 excavations did not reveal marked segregation of food
84 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

i 0.6 - 0.76m depth

(2-2.5 ft;

Hardpan soil

- 5.5m -

(18 ft)

deep passageways

entering hardpan

Plugged

Sit ranee

• 0.3"> -

(1.0 ft)

FIGURE 48.—Burrow-structure of an adult male, excavated 10 May 1975: a, side view; b, top

view. (Approximate depths, in meters, included inside circles for overhead view; H = minor

hoard; HOARD = major hoard; NEST = location of cavity filled with nesting material, crushed

leaves.)
NUMBER 265 85

0.46 - 1.2m depth

(1.5 - fc ft)

Hardpan soil

- 7.3m -

(24 ft)

©

Batranees

I- 0.>

(1.0 ft)

deep passageiwy

entering hardpan

FIGURE 49.—Burrow-structure of an adult female, excavated 20 June 1975: a, side view; b, top

view. {Approximate depths, in meters, included inside circles for overhead view; H = minor

hoard; HOARD = major hoard; NEST = location of cavity filled with nesting material, crushed

leaves.)
86

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Entrance

O.9 - 1.07m depth

(3 - 3-5 ft)

Hardpan soil

- 3.3m •

(11 ft)

Entrance

• 0.3m

(1.0 ft) deep, tapered

passageways entering

hardpan soil

FIGURE 50.—Burrow-structure of an adult male, excavated 1 June 1974: a, side view; b, top view.

(Approximate depths, in meters, included inside circles for overhead view; H = minor hoard;

HOARD = major hoard; NEST = location of cavity filled with nesting material, crushed leaves.)
NUMBER 265 87

types in the hoards, although trout lily bulbs were

only found in nesting material at the bottom of

the nest cavity.

It is notable that one burrow contained approximately 100 red maple seeds (Table 29). Since the

red maple seed crop had not yet matured at the

time of excavation (14 June), the seeds must have

been hoarded at least a full year earlier. Their

dark coloration and dried appearance attested to

their age. I subsequently germinated the seeds in

the lab, verifying their viability. This important

discovery points out that chipmunks have the potential to hoard seeds and nuts in viable condition

for time spans much longer than the winter period.

On 4 July 1974, I was monitoring the mating

activities of a female on the study plot. While she

was involved with males, a neighboring female

intruded into her burrow and made off with a

minimum of four pouchfulls or approximately 100

hoarded beechnuts (p. 40). More nuts were probably removed before I came upon the scene. This

places the lower limit of beechnut storage at approximately 9 months, and infers they can be

stored for much longer periods.

Table 30 lists the hoard compositions of three

burrows I exacavated in the spring and early summer of 1975, following the abundant beechnut and

sugar maple seed crops of fall 1974 (Table 23). The

strikingly large numbers of items recovered from

these three burrows is evident, one burrow containing 5460 beechnuts in early May. This is due

not only to large scale hoarding during the previous

fall in response to the abundant seed crops, but

also to extensive hoarding of overwintered beechnuts that were abundant in the leaf litter through

May.

The hoards I uncovered in 1975 were not only

larger than those I uncovered in 1974 (cf. Tables

29, 30), they were also more varied. Along with

large numbers of beechnuts, all burrows contained

sugar maple seeds and striped maple seeds. Red

maple seeds were common in two burrows. They

were at least a year old and still viable. One chipmunk hoarded large amounts of yellow birch seeds

(Table 30) in response to the extensive crop during

the winter of 1975 (Table 23). However, the

lesser weights of the seeds (Table 28) made them

an almost negligible food source.

The burrow I excavated on 10 May 1975 (Table

30) contained only two trout lily bulbs, chipmunks

at that time foraging on overwintered beechnuts

(see "Spring and Summer Foraging Behavior").

However, the two I excavated on 20 June contained

549 and 608 bulbs, reflecting high levels of foraging on bulbs during early June. I found small

numbers of seeds of the trout lily in the same two

burrows. In addition, I recovered bulbs of two other

wildflower species from one burrow (dwarf ginseng,

Panax trifolius, and spring beauty, Claytonia caroliniana). Flowering in early June, both species are

relatively uncommon in the study area and I never

directly observed chipmunks excavating their bulbs.

Most food items were hoarded in galleries or side

pockets, but two burrows had substantial hoards

mixed with crushed leaves at the bottom of the

nesting cavity. Segregation of items by species was

not striking, although one burrow contained two

segregated hoards, one of beechnuts and the other

of trout lily bulbs.

FACTORS AFFECTING STORAGE SPAN OF FOOD.—

Food items cannot be stored indefinitely and several factors work against the chipmunk in this

respect. Nearly all beechnuts in every hoard I examined showed signs of sprouting. Evidently, the

moisture levels in burrows are sufficient to induce

germination. If left unchecked, it is probable that

the nuts would take root, swell, and shed their

seed coats, making them more unsuitable for storage. Chipmunks react to sprouting in an interesting

manner: almost without exception, every sprouted

beechnut had its sprout neatly nipped off. Apparently, chipmunks remove the sprouts, an action that

retards germination. Fortuitously, they may derive

some nutrition from the consumption of the sprouts.

Sugar maple seeds were also prone to sprouting.

I found some germinated with unfolding leaves.

Unlike beechnuts, their sprouting was left unchecked by the chipmunks. Many sugar maple seeds

in the food hoards were rotting. Apparently, they

do not store well. Some beechnuts were also rotting, the nuts being attacked by a blue mold. The

seeds of red maple and striped maple appeared to

store well. Few seeds of either species (the red

maple seeds were nearly one year old) showed signs

of rotting or germination. The stored bulbs were

all products of spring hoarding (less than 1.5

months storage) and showed no signs of deterioration.

These observations reveal that chipmunks must

contend with the processes of germination and
88 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

rotting, both processes reducing the effective storage time of food items. Chipmunks may retard their

effects by storing items in dry chambers and by

nipping sprouts from germinating seeds. However,

another factor may be a far more serious threat,

especially to the chipmunk's critical beechnut store.

I found small adult tenebrionid beetles (Tenebrionidae), usually in abundance, among hoarded

seeds and nuts in all burrows that I excavated. The

larvae of these beetles attack the seeds and nuts,

burrowing into their centers to consume tissue.

Examing the hoarded food items shortly after

excavation, I found no evidence of serious larval

damage. However, beechnuts from infested hoards

that I subsequently stored under mild refrigeration

became thoroughly infested with larvae by late July.

It is possible that the beetle's life cycle is timed

such that damage to nuts and seeds occurs only during the late summer period. The large number of

beetles in all burrows that I excavated indicates

that larval infestation was imminent in all the chip

munk food hoards. I did not excavate any food

hoards in late summer or fall to assess damage.

However, it is probable that late summer insect

damage substantially reduces the size of most beechnuts food hoards, unless chipmunks have special

behavioral responses designed to reduce levels of

predation.

Sifting through nest material I found an abundance of small arthropods. Pseudoscorpions (Chelonethida) and small mites (Acarina) were exceedingly common in all nests. I also captured fleas

(Siphonaptera), but they were never so common as

to indicate serious infestation.

FOOD STORAGE AND ENERGETICS.—Several studies

have been performed measuring the metabolic rates

(oxygen consumption) of eastern chipmunks under

different ambient temperatures (Ta) for both normothermic and torpid or semi-torpid individuals.

Neal and Lustick (1975) defined the thermoneutral

zone for chipmunks as ranging from 28° to 35° C,

with oxygen consumption averaging 1.21 cm3 O2/

gm/hr in the zone. They found oxygen consumption below 28° C to be confined by the equation

cm3 O2/gm/hr = 4.25 - 0.10 T,. Neumann (1967)

defined the thermoneutral zone as 28° to 36° C

and found a metabolic rate of 1.25 cm3 O2/gm/hr

in this range. Neumann described metabolism below

28° C with the equation cm3 0,/gm/hr = 4.42 -

0.11 T .

Wang and Hudson (1971:65) placed the thermoneutral zone at 28.5° to 32.0° C and derived the

following equation for metabolic rate below 28.5°

C: cm3 O,/gm/hr = 4.47 - 0.12 Ta. They found

metabolism in the thermoneutral zone to be 1.03

cm3 O2/gm/hr. This value is somewhat lower than

those calculated by the other investigators; this may

be partially explained by the fact that Wang and

Hudson defined a relatively narrow thermoneutral

zone. The average metabolic rate in the thermoneutral zone for all three studies combined is 1.16

cm3 O2/gm/hr.

The values related above were derived from resting, normothermic animals. Investigators have long

been aware that the eastern chipmunk may enter

torpid states of decreased metabolic rates during

the winter months (Cade, 1963; Condrin, 1936).

Both Neumann (1967) and Wang and Hudson

(1971) studied the phenomenon of torpidity in the

eastern chipmunk and measured metabolic rates of

torpid animals.

Neumann, who gathered his experimental animals near Syracuse, New York, observed torpidity

at ambient temperatures varying from 0° to 22° C,

with the frequency of torpidity being greatest from

January through February. He found torpidity to

be sporadic, rarely lasting over 24 hours in length,

although torpid periods often occurred in cycles

during the winter period. The metabolic rates of

semi-torpid animals at ambient temperatures of

7° to 10° C varied from 0.5-0.8 cm3 O2/gm/hr.

Nontorpid or normothermic individuals, during

the summer months, exhibited 3.7-4.0 cm3 O2/gm/

hr metabolic rates in the same temperature range.

Deeply torpid individuals at 15° to 22° C had

metabolic rates ranging from 0.04-0.4 cm3 O2/gm/

hr. It is obvious from this data that torpid or semitorpid animals may effectively decrease their metabolic rates to levels 10% or lower than their normothermic rates for particular ambient temperatures.

Wang and Hudson (1971:60) gathered their experimental animals near Ithaca, New York. Of the

61 animals, 52 exhibited torpor at some time from

11 November through 29 May, at ambient temperatures ranging from 1.5° to 25.8° C. The majority

had torpor phases lasting from 20 to 130 days within which repeated episodes of torpor were observed.

It is obvious from this data that much variability in

frequency and degree of torpidity exists between in-
NUMBER 265

89

dividuals. Perhaps, too, large differences exist between populations at different latitudes. Wang and

Hudson (1971:73) found oxygen consumption during torpidity to range from 0.06-0.73 cm3

 O2/gm/

hr, these values being similar in magnitude to those

reported by Neumann (1967).

Evident from the studies on torpidity is the difficulty in determining average metabolic expenditures over the winter months. Not only does an

individual's metabolism fluctuate widely, but variation exists between individuals, between geographical locations, and probably between years. It would

be difficult to estimate the amount of food needed

for the entire winter period without measuring the

entire winter metabolic expenditure of individuals

at specific locations under natural conditions.

Further difficulties arise if winter metabolism

depends upon the state of the food hoard. Small

hoards, along with low temperatures, may induce

torpor under natural conditions. However, Neumann (1967) and Wang and Hudson (1971) did

not find strong correlation between these factors.

To gain more information about winter metabolism, I measured food consumption in six captive chipmunks (captured at Rock Creek Park in

Washington, D.C.) over three months from 27 November 1974 to 21 February 1975. The chipmunks

were housed in separate plastic burrow systems

("Habitrail," produced commercially for hamsters),

connected to a large wooden box. The wooden box

was subdivided with wire mesh into six chambers,

each chipmunk having access to one chamber. The

plastic burrow systems were kept covered and dark,

while the chambers in the box were illuminated

with overhead incandescent bulbs regulated by an

automatic timer to mimic outdoor light conditions

in Washington, D.C, during the time interval of

the experiment. The entire setup was housed in an

indoor environmental control chamber at the National Zoological Park that was maintained at an

ambient temperature of 10° to 15° C for the 3-

month period.

I offered excessive amounts of food (peanuts and

sunflower seeds) to each chipmunk in the lighted

chambers during the period from 27 November

through 25 December, the chipmunks storing large

amounts of this excess in their plastic burrow systems. In this way, my setup induced natural hoarding behavior. After 25 December I stopped feeding

and the chipmunks relied entirely on their food

hoards until the termination of the experiment. I

provided water continually throughout the experiment, and treated it with a vitamin and mineral

additive to avoid nutritive deficiencies.

By keeping track of the weights of food offered

and the amounts left unused, and by periodically

removing and weighing the food hoards in the

artificial burrow systems, I was able to estimate

food consumption over the 3-month period. The

data are presented in Table 27, which shows average consumptions (N = 6) of the food items during

each of the three months of experimentation.

TABLE 27.—Data derived from an experimental study of winter metabolism

(N = 6 chipmunks)

27

26

25

Dates

Nov to

Dec to

Jan to

25

2k

21

Dec...

Jan...

Feb.•.

Food item

Peanuts

Sunflower

seeds

Peanuts

Sunflower

seeds

Peanuts

Sunflower

seeds

Average dry weight

ingested per month

(gm)

132.8

20.0

117.2

16.8

98. k

30.8

Calories

ingested

per hour

1180

176

ioto

1U8

872

270

Calories

metabolized

per hour

1288

1128

108U

Average

of chi

(go

102

106

96

weights

pminks

t

.7

.3

.0

Metabolic

rate

(cal/gm/hr)

12.5

10.7

11.3
90

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

I estimated caloric content of peanuts and sunflower seeds (meat only) from tables in The Atlas

of Nutritional Data on United States and Canadian Feeds (U.S. National Research Council and

Canadian Department of Agriculture, 1971). Willson (1971:416) points to the danger of deriving

caloric values in this manner, since the values

may differ with the variety, growing conditions,

etc., of the seeds. Still, these values (5880 cal/gm

dry weight for sunflower seeds; 5970 cal/gm dry

weight for peanuts) are somewhat intermediate

when compared to caloric values of other plant

seeds cited in the literature (Willson, 1971; and

Harmeson, 1973; Grodzinski and Sawicka-Kapusta,

1970; Kendeigh and West, 1965) and probably are

accurate within 10 to 20 percent. Extreme accuracy

is not needed to draw relevant conclusions.

Both peanuts and sunflower seeds are very high

in ether extract (The Atlas of Nutritional Data on

United States and Canadian Feeds, 1971), indicating

lipid contents approaching 50%. Smith and Follmer

(1972) found digestive efficiency in squirrels to be

directly correlated with lipid content, nuts with

30% lipid content having 94% of their calories

metabolized. In determining calories metabolized

per hour by chipmunks (Table 27), I assumed 95%

efficiency of caloric utilization.

Metabolism (cal/gm/hr) ranged from 10.7 to

12.5 through the three months of experimentation.

This is comparable to the normothermic metabolic

rate for ambient temperatures in the 10° to 15° C.

range. Wang and Hudson (1971:65) derived the

equation cm3O2/gm/hr = 4.47 - 0.12 Ta for

normothermy below 28.5° C. Substituting 12.5° C

for T,, the calculated O2 consumption is 2.97 cm3

O*/gm/hr. This can be converted to caloric metabolism by assuming 4.8 kilocalories per liter of O2

consumed (Fulton, 1946:1094), the conversion being 14.3 cal/gm/hr.

Comparing my estimates with this estimate indicates that my experimental chipmunks conformed

approximately to normothermy for the three winter

months. This is in line with the fact that I never

saw any signs of torpidity during the experiment. I

provided nesting material (leaves and toilet paper),

but the animals tended to mat it down. Perhaps

poor insulation contributed to the maintenance of

normothermic metabolic rates. Perhaps, too, the

collection of my experimental animals at a southerly latitude (Washington, D.C., 38.9° N) further

reduced the probability of torpid states. It is my

feeling that my experimentally determined winter

metabolic consumption cannot be used to estimate

food needed to survive an Adirondack winter, chipmunks on my northerly study area (44.7° N) almost

certainly entering torpid or semi-torpid states periodically during the winter months.

THE SPRING BURROW-HOARD.—In order to derive

estimates of the length of time spring food hoards

can sustain individual chipmunks, I measured the

dry weights of sample food items found in the 1975

excavated food hoards. (Table 28). Grodzinski and

Sawicka-Kapusta (1970) surveyed the literature and

found the average energy content for seeds (minus

coats) of deciduous trees to be 5680 calories; I used

this estimate of calories per gram of dry weight

for my calculations.

Beechnuts comprised the major portion (in dry

weight) of all food hoards I uncovered. I found no

caloric measurements for American Beech (Fagus

gradifolia) in the literature. Gradzinski and SawickaKapusta (1970) found European Beech (Fagus

sylvatica) to contain 6976 cal/gram dry weight, a

value substantially higher than the deciduous tree

average. Perhaps American Beech is also high, making my estimates of hoard longevity slightly low.

To estimate the total calories available for metabolism in the food hoards, I assumed a digestive

efficiency of 85%, based on data provided by Smith

and Follmer (1972) for squirrels. They found digestibility (the ability to metabolize ingested calTABLE 28.—Dry weights of food items

burrow hoards

found in excavated

Species

Beechnuts

(without skins)

Sugar maple seeds

(without skins)

Red maple seeds

(outer skin removed)..

Striped maple seeds

(outer skin removed)..

Yellow birch seeds

(with wing and seed

Trout lil y bulbs

(without skins)

Spring beauty bulbs

(whole bulb)

Dwarf ginseng bulbs

(whole bulb)

Sample

size

18

2k

15

15

100

3^

35

15

Average

dry weight/item

(gin)

0.153 + 0.050

0.027 + 0.008

0.010 + 0.002

0.021 + 0.003

0.0016

0.054 + 0.025

0.069 + 0.0U3

0.320 + 0.166
NUMBER 265 91

ories) to be correlated with lipid content, 85%

digestibility corresponding to 20% lipid content.

This is probably low for American Beech, the lipid

content of European Beech being 30.5% (Grodzinski and Sawicka-Kapusta, 1970). By assuming a

slightly low value, I avoid overestimating potential

food hoard longevities.

I used Neumann's (1967) estimate of metabolic

rate (1.25 cc/gm/hr) to calculate metabolic needs

during the summer months. This rate assumes a

resting, normothermic animal in the thermoneutral

zone (28° to 36° C). This is probably equivalent

to a chipmunk resting in his burrow, next to his

food hoards, during the warm summer months. I

assumed that metabolic increase due to aboveground foraging during the summer is at least offset by the collection of new food items; otherwise

it would not be beneficial for chipmunks to waste

energy foraging. I converted the oxygen consump

tion metabolic rate to caloric consumption by assuming 4.8 kcal/liter O2 (Fulton, 1946:1094). This

produces a caloric expenditure of 6 cal/gm/hr. For

an 85 gram adult chipmunk (Table 14), this is

equivalent to 510 cal/hr or 12.2 kcal/day metabolic

expenditure. I use 12.2 kcal/day as the caloric need

of chipmunks for calculations of hoard longevity.

Tables 29 and 30 present the burrow-hoard

longevity data for 1974 and 1975. The total dry

weights of the 1974 food hoards are substantially

lower than the 1975 hoards, reflecting the moderate

beechnut availability during the fall of 1973 and

the abundant beechnut and sugar maple seed crops

of fall 1974 (Table 23). The estimated longevities

of the three 1974 hoards ranged from around 1 to 5.5

months, one adult male having enough food stored

to last at least until nuts and seeds were again

available the following fall. The other two individuals, obviously, would have to supplement their

hoards through the summer months to survive with

health until fall.

The estimated longevities of the three 1975

hoards ranged from around 6.5 to 11 months (Table

30). These high values indicate that all three chipmunks had enough food stored to last well into

the following winter. One adult male potentially

had enough food to last until the next spring, especially if his metabolic rate decreased with torpidity

during the winter months and if few seeds were lost

through rotting, germination, or insect predation.

The critical data on winter metabolism in the

Adirondacks is not available.

The importance of the spring hoards for sumTABLE 29.—Burrow-hoard contenu and data for 1974 on estimated hoard longevity

(dash = < 0.5 gramn)

Excavation date of burrow,

resident and hoard contents

Number of

food items

2700

1

1

17

1290

100

312

2

Dry weight

equivalents

(gm)

-

-

1

klk

197

1

17

_

Estimated Estimated

total energy longevity

content of hoard of hoard*

(kcal) (days)

1 June 197^: Adult

Beechnuts

Red maple seeds

Black cherry seeds.

Trout lily bulbs...

Total

June 1971*: Adult a

Beechnuts

Red maple seeds..

Trout lily b»ilbs.

Fern fronds

Total

Ik June 1971*: Adult 9

Beechnuts I+89

215

75

2351

1221

30

•Assuming metabolic needs of 12.2 kcal/day and 85$ digestibility.
92

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 30.—Burrow-hoard contents and data for 1975 on estimated hoard longevity

(dash = < 0.5 grams)

Excavation date of burrow,

resident and hoard contents

10 May 1975: Adult d1

Beechnuts

Striped maple seeds

Sugar maple seeds

Trout lil y bulbs

Total

20 June 1975: Adult 9

Beechnuts

Sugar maple seeds

Striped maple seeds

Red maple seeds

Trout lily bulbs

Trout lil y seeds

Total

20 June 1975: Sex unknown

Beechnuts

Sugar maple seeds

Striped maple seeds

Red maple seeds

Yellow birch seeds

Trout lily bulbs

Trout lily seeds

Dwarf ginseng bulbs

Spring beauty bulbs

Total

•Assuming metabolic needs of

Estimated Estimated

Dry weight total energy longevity

Number of equivalents content of hoard of hoard*

food items (gm) (kcal) (days)

1560

1970

2

835

33

53

921

31*+1

kok

90

1008

5^9

10

11

2

10

30

_

531+

2U38

1566

501

156

100

608

32

88

150

373

k2

11

2

_

33

28

10

^99

1+7U2 330

3033 211

283U 197

12.2 keal/day and 85% digestibility.

mer, fall, and winter survival during 1975 was

multiplied by the beechnut and sugar maple seed

crop failure during the fall of 1975. The chipmunks

probably supplemented their hoards with red maple

seeds and trout lily bulbs during the early summer

period. However, no new food items were available beyond August of 1975, and nearly all chipmunks had disappeared into hibernation by late

September (see "Autumn Foraging").

A major point derived from my data on burrowhoarded food is that the hoard is critical for times

other than the harsh winter months. Almost certainly, the hoard is relied on extensively during

the late summer lull in above-ground activity. In

addition, during years of fall seed crop failure,

hoarded food from the previous fall and spring may

become critical for survival through the winter

period. Thus, chipmunks may sometimes rely on

seeds and nuts gathered a year or more in advance.

INTERSPECIFIC COMPETITION FOR FOOD RESOURCES

The red spruce and balsam fir cone crops in the

mixed woods near the study site were nearly a complete failure during late summer and fall of 1973

(Table 23). In response, red squirrels (Tamiasciurus

hudsonicus) set up territories in the hardwoods

during early fall and utilized the moderate beechnut crop ripening in the trees at that time. By late

September 1973, one red squirrel was utilizing a

portion of the study grid and I observed his interactions with resident chipmunks whose home ranges

overlapped his territory.

The red squirrel aggressively chased the chip-
NUMBER 265 93

munks when he encountered them on the ground.

In one instance, I watched the red catch a chipmunk and inflict a bloody wound by biting. The

chipmunk, however, survived and the wound

healed. At least seven chipmunks utilized his territory regularly, and the red squirrel appeared unable to effectively defend the area from them.

The red squirrel collected beechnuts by foraging

in the crowns. He severed burrs at their basal attachment and let them drop to the ground. After

5 to 10 minutes of crown foraging, he usually descended and collected the freshly dropped burrs,

transporting each burr singly to locations near the

center of his territory. There he buried them in

the leaf litter, usually caching 20 to 30 burrs (each

containing 2 nuts) in the same hole. I never observed the red squirrel to hoard large amounts in a

central location as red squirrels are known to do

with cones in coniferous woods (Smith, 1968:58-59;

Merriam, 1886:214). The red squirrel lived in an

underground burrow just off my study area; I never

saw him transport food into his living quarters.

I feel that the foraging and hoarding habits of

the red squirrel made his food supply quite vulnerable to foraging chipmunks. I observed chipmunks

picking up burrs (and removing nuts) under crowns

while the red squirrel was busy dropping them

from above. It is probable that chipmunks also located and pilfered many of the scatter-hoards made

by the red squirrel, although I never directly observed it. I noted no red squirrel utilization of the

abundant beechnut and sugar maple seeds during

fall 1974. However, the red spruce and balsam fir

cone crops were also excellent, negating the need

for red squirrels to migrate out of their preferred

mixed forest habitat.

Two species of nocturnal flying squirrels inhabit

the forest surrounding the study site (Glaucomys

sabrinus and G. volans). It is well known that G.

volans makes food caches in the autumn (Muul,

1968:18; Sollberger, 1943) and that seeds and nuts

are a favored food item. This species sometimes

caches nuts singly, but is also known to lay away

large hoards in the hollows of trees (Jackson, 1961:

179); it almost certainly utilizes beechnuts if they

are available during the fall season.

The habits of the northern flying squirrel (G.

sabrinus) are not well known and no direct accounts of food hoarding have been reported in the

literature. However, Merriam (1886:207) does mention that it is fond of beechnuts. Apparently, G.

sabrinus is restricted mainly to mixed woods, while

G. volans prefers hardwoods (Jackson, 1961:177).

Neither species hibernates, although G. volans may

enter torpidity (Muul, 1968:47). Both species probably rely on hoarded food for winter survival.

The nocturnal deermouse, Peromyscus leucopus,

were abundant on the study area. They are somewhat arboreal, nests being found in tree hollows as

high as 21 m (70 ft) (Merriam, 1886:263). This

species lays up large hoards of food items in the

fall, usually in holes in trees or hollows logs. Merriam (1886:264) mentions that beechnuts are a

favorite food and that he usually shucks the nuts

by removing the burr and the woody seed coat before hoarding. A local logger, Tom Kilfoyle (pers.

comra.), has uncovered large hoards of 500 or more

shucked beechnuts in tree hollows. These hoards

were probably made by P. leucopus, but may have

been the doings of Glaucomys spp. The whitefooted mouse, Peromyscus maniculatus, inhabits

Adirondack hardwoods and is known to make food

hoards (Howard and Evans, 1961). Neither species

of Peromyscus are hibernators and both probably

rely extensively on food hoards for winter survival.

Red-backed voles (Clethrionomys gapperi) are

also common in the hardwood forest. Both Merriam (1886:271) and Jackson (1961:228) mention

that they will feed on beechnuts. These voles are

not known to make extensive food hoards, but I

have observed individuals in the Adirondack region scatter-hoarding sunflower seeds gathered at

bird feeders.

Shorttail shrews (Blarina brevicauda) were common on the study area, especially during the spring

of 1975, following the excellent fall 1974 seed and

nut crop. Although shrews are predominantly insectivores, the shorttail does consume and hoard

seeds and nuts. I observed one shrew near my study

area hauling away for storage hundreds of sunflower

seeds that I was using to attract chipmunks for

photography. Shorttail shrews probably gather large

quantities of beechnuts and other seeds from the

leaf litter. They may also periodically pilfer chipmunk scatter-hoards made during the summer

months. Merriam (1886:169) found captive shorttail shrews to relish beechnuts, and Jackson (1961:

51) mentions their affinity for the same.

Various bird species also feed on nuts and seeds.

I noted blue jays (Cyanocitta cristata) foraging in
94

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

the crowns for beechnuts during the autumns of

1973 and 1974. Dr. Eugene Morton (pers. coram.)

of the National Zoological Park has observed blue

jays hoarding nuts under bark and under leaves

on the ground. Evidently, blue jays can transport

several nuts at a time in their mouth cavity. Periodically, large migrating flocks of purple grackles

(Quiscalus quiscula) set down in beech crowns to

forage upon nuts. Nuthatches (Sitta carolinensis and

S. canadensis) and chickadees (Parus atricapillus),

common birds in the Adirondacks, also utilize a

portion of the seed crops.

I have treated elsewhere the topic of insect predation on burrow-hoarded nuts (p. 88). I did not

assess insect damage to beechnuts and sugar maple

seeds prior to their ripening in the tree crowns, but

insect predation potentially could drastically reduce the number of seeds or nuts reaching maturity. I mentioned earlier (p. 81) that heavy insect

larval predation in a black cherry tree in the study

area resulted in the premature dropping of unripe

berries during one year.

DISCUSSION

In reviewing the literature, I found a noteworthy

lack of recent inquiries into the foraging ecology

of the eastern chipmunk. In spite of this, I did

locate many other useful references to chipmunk

foraging behavior primarily from the notes of early

naturalists such as C. H. Merriam, C. Kennicott,

J. J. Audubon, J. Bachman, and J. Burroughs. A

great portion of this information is summarized

and expanded upon by E. T. Seton in his Lives of

Game Animals (1929). It is somewhat comforting

to discover that these men had their eyes wide open

to the events of natural history, and, that after an

apparent void of forty years or more, many of

their observations can be verified and are of relevance to contemporary ecological investigations.

VARIABILITY IN FORAGING BEHAVIOR.—The best

demonstration of year-to-year variability in foraging

behavior in response to resource availability levels

was the switch from crown foraging for beechnuts

during the moderate crop of 1973 to ground foraging during the abundant crop of 1974 (see "Autumn Foraging," Table 23). Descriptions of crown

foraging are rare in the literature (except for shrubs

and small trees), but Merriam (1886:238) recalls

observing chipmunks gathering beechnuts at heights

approximating 18 m during early November. He

saw an individual making regular journeys from

his burrow to the crown, evidently transporting

pouchfulls into his burrow. Merriam did not specify

if the chipmunk climbed directly up the beech

trunk. I found no mention in the literature of the

use of rough-barked species (such as sugar maple)

as "ladders" lending access to beech crowns. The

presence of the complicating factor of bark texture

as it relates to climbing ability adds a new dimension to the study of crown foraging. Perhaps crown

foraging in beech trees is not feasible in areas lacking rough-barked access species.

Variability related to seasonal changes occurred

in hoarding behavior. Scatter-hoarding was common in the spring and early summer, while burrowhoarding was the predominant adult hoarding pattern during the autumn. The data indicate that

most scatter-hoards are temporary and are removed

to the burrows within a day or two after they are

made (see "Scatter-Hoarding Behavior"). Some

chipmunks appeared to "remember" the exact

whereabouts of food caches made several hours

earlier, making directed movements to them and

transporting the food into their burrows.

Merriam (1886:235) described scatter-hoarding

behavior in the Adirondack chipmunk, but his

account is not detailed. Kennicott (1857) remarked

that scatter-hoarded caches are probably for temporary use, small caches being transferred to the

central (burrow) hoard long before winter. My

observations verify Kennicott's assertion.

The adaptive value of scatter-hoarding was not

readily apparent in my study. Food gathered on

all portions of the home range was scatter-hoarded.

Further, scatter-hoards were often made quite close

to the home burrow (within 3 m), where transport

of the food items into the burrow would have required no increase in time or energy. Scatterhoarded food items may undergo a drying or "curing" process during their sojourn in the leaf litter,

similar to the curing of seeds scatter-hoarded by

desert heteromyid rodents (Shaw, 1934). However,

I feel this to be unlikely because the moist and

shady conditions of the Adirondack hardwood leaf

litter would induce germination, a process opposed

to the successful storing of seeds and nuts.

The only mention of scatter-hoarding behavior

in recent literature is by Yahner (1975). He ob-
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95

served chipmunks scatter-hoarding single acorns in

early September and switching entirely to burrowhoarding by late September. Yahner also did not see

an apparent adaptive value, noting scatter-hoarding

at many locations in the home range. He brings up

the possibility that scatter-hoarding may be a vestigial behavior reflecting the phyletic history of the

species. Yahner points out that scatter-hoarding is

common in tree squirrels of the genus Sciurus. It

is my feeling that scatter-hoarding must be adaptive. The predominance of this mode of hoarding

during early summer on my study area was obvious.

If it were not adaptive, there would be strong selection against the wasting of time, energy, and food

on inefficient behavior. I am at a loss, however, to

offer a logical argument for its adaptability.

FOOD ROBBING.—I observed pilfering of burrowhoarded food three times during my study, twice

in response to the disappearance (due to dispersal

or death) of resident chipmunks from their burrows. The most interesting case was the pilfering

of a female's burrow-hoarded beechnuts by a neighboring female when the resident was in estrus and

was being pursued by male consorts on her home

range periphery (p. 81). Some males involved in

the mating chase entered her burrow, but none

made off with food. Obviously, if the breeding

males removed part of her hoard, they would potentially lower the survivorship of their own progeny. One would expect considerable inhibition

among the males against stealing the hoards of females, especially during breeding season. Of interest here is my observation that foraging behavior

seemed to be incompatible with sexual behavior in

males during the summer breeding season (p. 79).

The only reference to burrow pilfering that I

located was by Burroughs (1919:144-150). Burroughs relates three occasions during the autumn

when he noted chipmunks raiding their neighbor's

stores. Usually, the residents intercepted intruders

and chased them from the burrow. Burroughs was

unclear about how much food the robbers made

off with, but he did mention that one carried away

items in his pouch. Burrow pilfering may be a

serious threat to the resident's hoard, and one

towards which he must exercise constant vigilance.

I have no idea how frequently robbing occurs in

the natural population.

TYPES OF FOOD ITEMS.—The types of food items

utilized by chipmunks on my study area (Table 25)

correspond closely to item use reported by other

authors. Nearly all investigators refer to the utilization and storage of edible seeds and nuts produced

by mature hardwood species (see Allen, 1938, for a

review). The tree species, of course, vary with locality. The consumption and storage of edible bulbs

and tubers is not mentioned in most studies, although Merriam (1886:236) observed the following:

On the western side of the Adirondack region the chipmunk feeds largely upon the tuberous roots of the dwarf

ginseng . . . (Aralia trifolia) . . . and the yellow grain-like

tuber of the unspurred dicentra . . . (Dicentra canadcnsis).

He makes no reference, nor do other authors, to

the use of trout lily bulbs (Erythronium americanum); these bulbs were heavily utilized by chip

munks on my study plot, especially during the

spring and early summer.

Most authors have agreed that perishable items

constitute a minor part of the chipmunk's diet.

Allen (1938) reviews the literature concerning the

periodic consumption of insects and other arthropods. I observed chipmunks eating newly unfolded

leaves of beech and sugar maple saplings; Allen

(1938:77) reported the eating of newly unfolded

elm leaves. Mearns (1899:352) reported that chipmunks in the Catskill Mountains readily consumed

the fruiting bodies of mushrooms. I did not observe

much mushroom utilization, although some chipmunks excavated and consumed subterranean puffballs (Lycoperdales).

I located several references to the consumption

of birds by chipmunks (e.g., Ginevan, 1971), but

the observations of William Brewster as quoted by

Seton (1929:201) are particularly interesting. Brewster shot and wounded a wood thrush which a

chipmunk subsequently pursued and killed. The

chipmunk then consumed the brain of the thrush.

This corresponds to my observation of a chipmunk

consuming the brains of two nestling winter wrens

(p. 80).

The food resources used by chipmunks during

my study can readily be divided into two categories

(Table 25). The first category includes all items

which are hoarded by chipmunks. Some of these

nonperishable food types comprise the major portion of the chipmunk's diet and considerable time

and energy is invested in their collection. Bulbs,

maple seeds, and beechnuts fall into this group.

Other hoarded items are listed in Table 25, but
96 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

these represent a minor portion of the total dry

weight of burrow hoards (Tables 29, 30). A second

category includes highly perishable items that are

not stored and that comprise a minor proportion

of the total diet. Foraging for items in this category

appeared nonsystematic, and relatively small

amounts of time and energy were devoted to their

pursuit. Insects and other arthropods, subterranean

fungi, new leaves, and bird brains fall into this

category.

SEASONALITY OF FOOD AVAILABILITY.—A predominant seasonal pattern in food availability within

the study area was noted for seed production in red

maple, sugar maple, and beech. Red maple seeds

ripen and fall during late June and are removed by

chipmunks by mid-July. Beechnuts and sugar maple

seeds mature from late September to October and

most are gathered during the autumn season. During years of abundant production, however, the

seeds and nuts may lie dormant under the snow,

providing an abundant food source during winter

snowmelts or for a short period during the spring.

The seasonal availability of trout lily bulbs is not

clear. Bulbs are available underground all year, but

it is problable that nutritional values of the bulbs

change with the season. Efficiency and intensity of

foraging on the bulbs underwent a decrease when the

above-ground leaves wilted away in mid-June. One

point is apparent concerning food availability: seasonal patterns are very predictable, maturation times

varying less than a week or two from year to year.

Figure 51 diagrams the seasonal availability patterns of the major storable food resources. For

comparison, I include a chart of the seasonal pattern of life history events for the Adirondack chipmunk. Note that the midsummer lull (late July

through August) in chipmunk activity coincides

with the gestation and nursing phases of adult females and with a period of low food availability.

Emergence and dispersal of the young coincides

with the appearance of food items in the spring and

fall.

Yearly variation in production levels of seeds and

nuts is marked (Table 23) and probably highly

unpredictable on a year to year basis. Long term

cycles may exist, but no data is available for the

Adirondack region. Probably, inclement weather

during the flowering period for each species (May)

radically affects the seed crop success. Further, some

species may be unable to produce large crops each

| TBtTORAL AVAIIAHriJTY OF MAJOR FOOD ITEMS |

red maple sugar maple

Trout lily bulbs seeds beechnuts ^ seeds

—

JFMAMJJASOND J

| TBCORAI ASPECTS OF UFE CYCIS |

Hibernation

Spring Fall

emergence dissappearance

1 Midsummer lull ••

in activity

Spring and early summer

foraging and hoarding period

Fall foraging and hoarding

I 1 period

Breeding

i—i

Gestation

Breeding

Gestation

Nursing Nursing

Bnergence and dispersal of young

JFMAMJJASOND J

FIGURE 51.—a, Temporal availability of major food items in

study area (does not include yearly fluctuations in production levels for the different species); b, temporal aspects of

chipmunk life cycle to be compared with a.

year, even if environmental conditions are favorable. After the spring flowering period, flower remains drop to the ground. Chipmunks could derive

important cues concerning the impending autumn

seed and nut crops from the prevalence of such

remains.

BURROW STRUCTURE.—The burrow systems of the

eastern chipmunk have been described by Panuska

and Wade (1956) and Thomas (1974). Panuska

and Wade defined two types of systems: "simple"

and "extensive." Simple systems consist merely

of a tunnel with a slightly widened terminal end,

while extensive systems are a complex plan of

tunnels with large living and storing chambers.

Panuska and Wade excavated 21 simple and 9

extensive systems, while Thomas excavated 33 simple and 17 extensive systems. I excavated only extensive systems used by resident chipmunks (see

"Structure of Burrows"). My descriptions of resident

burrow systems are similar in most respects to the

extensive systems decribed in both studies cited,
NUMBER 265

97

with the exception that Adirondack burrows demonstrated greater complexity of the tunnel system.

Further, neither Panuska and Wade nor Thomas

reported deep, tapered, dead end tunnels that may

function in drainage of the burrow system during

wet spells.

Simple systems are apparently not used for food

storage in the Adirondacks, as I never observed

food transported into any cavities other than the

home burrow. Panuska and Wade (1959) found

a dearth of stored food in all systems they excavated, while Thomas (1974) found some stores in

simple systems and larger stores in extensive systems. Thomas did not uncover extremely large

stores such as those I found in Adirondack burrows.

His excavations were made in Louisiana, where

winters are short and mild. He conjectured that

large stores may not be used under those climatic

conditions.

Like myself, Panuska and Wade and Thomas

usually found only one active entrance to extensive systems, although Thomas found plugged alternate entrances in some burrows. I also found

plugged entrances. I found no accumulated concentrations of feces (defecatoria) in home burrows,

and none were described in the two studies cited.

Toilet chambers, however, have been reported for

the eastern chipmunk (Calahane, 1947:380). I found

all home burrows to contain a large nest cavity

filled with crushed leaves. Panuska and Wade uncovered only one leafy nest. Thomas found cavities containing thin carpets of leaves (whole and

crushed), but did not describe cavities packed with

leaves. Perhaps insulation is not important at southerly locations.

FOOD AVAILABILITY AND THE BURROW-HOARD.—

The dynamics of burrow-hoarding are relevant to

a discussion of food availability because hoarding

effectively alters availability patterns (see "BurrowHoarding Dynamics"). The hoarding habit is certainly critical to winter survivorship; since chipmunks do not put on fat reserves, they need energy

reserves in the form of burrow-hoards during the

winter months. The burrow-hoard may also be

critical to Adirondack chipmunks during late July

and August, when no food items are abundant

above ground (Figure 51). The potential long storage of food items was demonstrated by the occurrence of viable year-old red maple seeds in spring

burrow-hoards. Further, the storage of beechnuts

for a period of ten months was demonstrated. My

estimates of energy content in spring hoards indicate that stores could potentially maintain individual chipmunks for periods up to ten months, and

maybe a year. Such long term storage may aid in

seeing chipmunks through years of low food availability, such as the winter of 1975-1976 on my

study area (Table 23).

FOOD RESOURCES PATTERNS AND SPATIAL DYNAMICS

Spatial and temporal patterning of food resources

in the environment is a critical factor in the determination of spatial structure in chipmunk populations. For this reason, I will integrate the descriptive data presented in this monograph with a

theoretical argument.

What set of circumstances allows and favors the

chipmunk's general mode of spatial organization:

a solitary, sedentary, defensive, and dispersed condition? Lifelong existence in one spot is only

allowed if food resources are available or can be

made available in that spot continuously. Since I

have demonstrated that temporal patterns of resource availability occur on my study site, then a

primary problem for chipmunks is how to survive

through periods of low availability. Chipmunks

hoard food during peak periods of food production

and utilize the hoards during periods of scarcity

(see "Dynamics of Burrow-Hoarding"). Torpid

states may lower metabolic requirements during

the winter months (Scott and Fisher, 1972). Hoarding activities and torpid states both buffer the

effects of temporal fluctuations in food availability,

allowing for a sedentary existence.

The advantages accrued to living at a fixed location are obvious. The individual learns details

concerning his home range that lead to efficient use

of the area's resources. Furthermore, an exact knowledge of the area leads to effective antipredator

responses. Also, individuals can construct and occupy elaborate living quarters (burrows in the case

of chipmunks) that would not be feasible for nomadic species. The chipmunk's burrow offers protection from predation during sleep or rest periods,

provides comfortable quarters during inclement

weather, and serves as a locus for hoarding activities.

A moderate degree of homogeneity or uniformity

in the distribution of most major food resources
98

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

occurs on the Adirondack site (see "Spatial Availability of Food Resources"). This allows the population to be uniformly dispersed or nearly so over

the hardwood habitat. In addition, it makes it

feasible for individuals to gather resources within

reasonable distances from their burrows. Long distance movements that tend to conflict with the

sedentary way of life are only resorted to under

special circumstances of food resource patchiness

(see "Long Movements for Red Maple Seeds"). Be

aware that I am only implying that resources are

homogeneous enough to allow for sedentary existence. Differences in the level or degree of homogeneity may greatly affect the fine-structure of spacing, even within the general framework of the

sedentary, solitary, aggressive, and dispersed condition.

The absence of pair bonding or the need for

bonding among most mammals has been discussed

by other authors (e.g., Orians, 1969). One of the

factors favoring a solitary life style is the phenomenon of lactation, which allows females to raise

young by themselves, thus dispensing with the need

for provisioning of the young by other individuals

(mates). Smith (1968:59) presents a mathematical

argument based upon foraging and hoarding efficiency that also helps to explain the advantage of

a solitary existence in red and douglas squirrels

(Tamiasciurus hudsonicus and T. douglasi). Similarities of the life styles of these squirrels and the

eastern chipmunk make Smith's arguments applicaable to the chipmunk.

The exhibition of defensive behavior by residents

(p. 26) has apparent adaptive value. It is advantageous for individuals to keep intruders out of

their home areas because they compete for available resources and potentially may rob food stores.

All of the above points combined describe conditions that both allow and favor a dispersed, solitary, sedentary, and defensive mode of life. In

nearly all respects, the conditions encountered on

my Adirondack study site conform to this set. Nevertheless some trends in saptial use exhibited by

chipmunks are not so easily explained.

The spatial structure of the chipmunk population can best be described as one where individuals are dispersed, solitary, and sedentary, but where

individual home ranges overlap considerably, and

where use-intensity (time spent per unit area) is

highest near the home range center and decreases

toward the peripheral area (Figure 12). In most

respects, the spatial structure is reminiscent of that

expounded by Calhoun and Casby (1958) for small

mammals, where home range use conforms to a

bivariate normal distribution, and where home

range centers are spaced approximately 2-sigma

apart (see Calhoun and Casby for a discussion of

sigma as a measure of home range use).

Dominance in social encounters is dependent

upon distance from home range centers (p. 40; Dunford, 1970:229), such that an individual only dominates in the central portions of his home range.

Hence, only a "core area" is actually defended. A

very obvious and straightforward series of questions

is: Why do home ranges overlap in the observed

manner? Why do chipmunks not divide up the

habitat so that each individual occupies and defends an exclusive area? Why do chipmunks not

restrict their movements to the core area?

The feasibility of a non-overlapping spatial system is exemplified by another Adirondack sciurid

which exists in sympatry with the eastern chipmunk. In the Adirondacks, the red squirrel (Tamiasciurus hudsonicus) is a common species in

mixed forest, especially red spruce-balsam fir flats

(Smith, 1968). My field observations during the

summer of 1973 indicate that red squirrels inhabiting Adirondack coniferous woods have a social

structure conforming to Smith's descriptions for

that species in the Northwest.

The red squirrel, like the chipmunk, is solitary,

sedentary, and dispersed. Furthermore, it is a food

hoarder, and is known to build large central caches

that are drawn upon during times of low food

availability. The primary utilized resources for red

squirrels in coniferous woods are mushrooms and

the cones of coniferous trees. The cones of most

species mature and are available for consumption

and hoarding in the autumn. Hence, they are comparable in terms of temporal availability to the

fall seed crop that forms the basis of the winter

hoard of the eastern chipmunk (see "Autumn Foraging"). The red squirrel does not normally inhabit burrows, but their tree nests are centrally

located in their home ranges in close proximity to

their underground hoards.

Red squirrels are aggressive and defend their

home areas from intruders. Smith (1968:33) observed shifts in dominance depending upon proximity to the home range center. The mating structure
NUMBER 265 99

of the red squirrel is comparable in many respects

to the mating structure I described for chipmunks

(cf. Smith, 1968:37-39; and "Mating Behavior").

No long term cohesive associations occur between

the mother and her litter in red squirrels, members of the litter becoming aggressive and dispersing soon after weaning (Smith, 1968:41-43). The

same situation occurs in the eastern chipmunk (see

"Juvenile Dispersal" and "Predispersal Social Behavior in the Litter"). In many respects, then, red

squirrels and chipmunks follow similar life

styles, both conforming to the sedentary, solitary,

dispersed, and aggressive mode of existence. However, there is one striking difference between the

two species.

Red squirrels inhabit discrete, non-overlapping

and contiguous territories in coniferous woods

(Smith, 1968:33-34), this being in contradistinction

to the overlapping home range system of the eastern chipmunk. Thus, the red squirrel demonstrates

that a non-overlapping type of home range system

is a real and feasible type of system for a sciurid.

Having demonstrated this, I ask again why chipmunks conform to the overlapping mode, or conversely, why the red squirrel has opted for the nonoverlapping mode. A possible explanation lies in

an analysis of the spatial patterning of food resources in the habitats of the two species. The

strong similarities between the two species in other

aspects of their life style greatly simplifies the following consideration.

I define several variables to help conceptualize

the spatial systems of the two species. This set of

measures is only meant to be applicable to species

conforming to the sedentary, solitary, and dispersed

mode of life.

Let A equal the average area for each individual

within a large sample population, calculated by

dividing the total area (T) of the sample by the

number of individuals utilizing the area (N). For

convenience, I assume the area T to be inhabited

by a relatively uniform distribution of individuals,

such that all portions of the habitat are utilized.

Hence, any references to densities of individuals

refers to "ecological density" as opposed to "crude

density" (Odum, 1971:163). If the average area (A)

is visualized as a circle, a hypothetical average

home range diameter (D) can be calculated as

being the diameter of a circle of area A. The value

D is a realistic measurement when we deal with

the red squirrel who exhibits roughly circular, nonoverlapping and contiguous home ranges in coniferous woods (see home range maps in Smith, 1968).

Let D equal the actual average home range diameter calculated by measuring actual home ranges

of all individuals within the sampling area T.

Thus, D is a real measurement derived from spatial use-patterns, while D is calculated from population density. D may or may not approximate D,

depending upon the spatial system of the species in

question. The relationships of these variables are

depicted in Figure 52. For the sake of clarity in

contrasting the two species, the D's for each species

are depicted as being equal in magnitude. In reality, D for chipmunks is probably much smaller than

that for red squirrels in most habitats.

Included in Figure 52 are two-dimensional representations of home range use and overlap. These

representations depict a cross-section through the

centers of four neighboring home ranges. Note that

in red squirrels, individuals (on the average) restrict their movements to the calculated A, hence

their actual average home range diameter (D) is

approximately equal to D. In chipmunks, the actual average home range diameter (D) is much

greater than D, due to the overlapping nature of

the home ranges.

An important point is made by assuming the

sampling area T can only support N animals because there is only enough food for N animals to

survive. This is akin to the notion of the carrying

capacity of the environment (see Odum, 1971:183),

and is dependent upon the reality of assuming that

food supply ultimately determines population

densities. The carrying capacity, of course, varies

from year to year and season to season, and there may

a

D=D D>D

cross section through

centers of four

ranges

FIGURE 52.—Home range use and overlap: a, red squirrel

discrete, non-overlapping, and contiguous territories with

aggressive defense; b, chipmunk overlapping home ranges

with aggressive defense <D = actual average home range

diameter; D = hypothetical average home range diameter).
100

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

be a lag in population responses to changes in immediate carrying capacity. These problems tend to

complicate the issue. For the sake of convenience

and clarity, I will consider carrying capacity as

remaining somewhat stable from year to year.

Assuming that T can support N animals, it follows that A can supply enough food, on the average, for a single individual. The importance of

the qualification "on the average" cannot be stressed

too greatly. It implies that there exists a probability (P) that any circular area equal to A that is

selected at random from the area T will produce

enough food to support a single individual. I feel

that this probability is very important to individuals in that it greatly influences their strategy of

spatial utilization. This probability value is largely

a reflection of the spatial patterning of food resources in the habitat. The more patchy or heterogeneous the food distribution is, the lower the

probability that adequate food will be found in

any randomly chosen circular area equal to A. It

follows that some of the areas would contain excess

resources and others would contain inadequate resources. The more homogeneous the food distribution becomes, the higher is the probability that

adequate resources will be found in a circular area

equal to A.

I propose that the value of the probability (P)

affects the strategies of individuals in the following

manner. If P is high, then the individual will concentrate his activities within a circular area of a

diameter_ approximating D and an area approximating A (Figure 52a). The best way to conceptualize this is by imagining N animals uniformly

distributed across area T, the number of individuals

being the product of the carrying capacity of T.

Through interactions with one another of an agonistic nature, each individual establishes his own

dominance arena. If P is high, the individual will

concentrate his movements within his dominance

area, which approximates A. The advantage of

visualizing the process in this manner is that it

allows for variability in home range size or domiance arenas due to individual differences in aggressiveness (see "Social Behavior with Chipmunk Population"). However, an individual possessing a

dominance arena less than A is not necessarily

doomed to death; he may only suffer lowered survivorship or lowered fecundity.

In the situation where P is low and food heterogeneity is high, it is advantageous for the individual to make periodic excursions out of his dominance arena so that he might locate patches of

concentrated food resources. If an individual were

to restrict his activities to his dominance arena,

then a great percentage of the time he may not

have enough food to survive in a healthy condition. However, it would be a useful strategy to

concentrate movements in the central portions of

the home range for two reasons. First, if patches

are available within the area A, they would be

located first, thus avoiding a wastage of time and

energy on lengthy excursions out of the dominance

arena. Furthermore, defense of the central portions

of the home range would be more efficient if individuals concentrated their activities in their core

areas.

It is expected, then, that a species with a low P

for a particular habitat would have a greater urge

or motivation for making periodic excursions into

neighboring core areas, and that, for many individuals, it would be fatal or very detrimental to

survivorship or fecundity if excursions were not

made. Of course, short term behavioral adjustments

to resource patterns would occur, allowing the individual to forfeit long excursions if food is abundant within his core area. However, seasonal and

yearly variations in fruiting levels of different tree

species and of different individuals within each

species would make patchiness somewhat unpredictable. This would keep foraging patterns of

individuals from becoming greatly stereotyped for

long periods.

Using the argument just presented, I propose

now to test if resource patterning in the red squirrel and chipmunk habitats can be used to explain

their disparate spatial systems. Data for red squirrels is drawn from Smith (1968) and data for chipmunks is derived from this study.

Smith provides quanitative data describing resource distribution for two populations of red squirrels in two different habitat types. The first population consisted of 13 individuals in a forest dominated by lodgepole pine (Pinus contorta). The

average home range size and standard deviation

for the 13 squirrels was 1.88 ± 0.83 acres (0.76 ±

0.34 hectares). The principle food types utilized by

red squirrels at this site were lodgepole pine cones,
NUMBER 265

101

terrestrial fungi, and a rust fungus (Peridermium

spp.) found on lodgepole pine bark.

Smith indicates that the terrestrial fungi are

uniformly distributed in the habitat and occur in

relatively high densities; his sampling areas for

mushroom production were small (4 quadrats, 15.25

m on a side). The rust fungus averaged 19.2 viable

growths per lodgepole pine tree. Therefore, the

spatial patterning of the rust can best be viewed

in terms of the spatial patterning of the lodgepole

pine trees. The average number of lodgepole pine

trees per territory was 166.6 (±89.19). As a measure

of the uniformity or homogeneity in the distribution of the lodgepole pine trees, I calculated the

average density of trees per territory and found

it to be 85.5 (±19.8) per acre or 211.2 (±48.9) per

hectare, indicating a fairly high level of uniformity.

This also indicates, as Smith rightly stated, that

food supply gained is roughly proportional to area

of territories.

At his other study site, Smith measured the territories of six individuals and found an average territory size of 1.01 (±0.52) acres or 0.45 (±0.21) hectare. The only major food item available at this

site during the year of study was the cones of western hemlock (Tsuga heterophylla). There was an

average of 62.2 (±18.8) trees per territory, and the

average density per territory was 70.5 (±26.0) per

acre or 174.1 (±64.2) per hectare, indicating that

the trees were not as uniformly distributed as at

the other site and that each territory contained

fewer trees.

Exact figures are not important here. Suffice it to

say that red squirrel territories appear to contain

at least 50, and often over 100, cone producing

trees (and Peridermium producing trees in lodgepole pine forests). If terrestrial mushrooms are consumed as a major item, their distribution is uniform and dense. What does this mean in terms of

resource patchiness? Obviously, terrestrial mushrooms are homogeneously distributed in terms of

red squirrel territories. Moreover, data indicate a

relatively uniform distribution of trees in both

habitats. Therefore, patchiness created from variation in densities of trees or mushrooms over the

habitat is not a major consideration. Assuming that

some variability exists in cone production or Peridermium production between individual trees

leads to the conclusion that patchiness is determined to a great degree by the number of trees

included in each territory.

We know from elementary statistics that increasing sample size (in this case the number of trees)

reduces the effects of variability among individual

units. A red squirrel, by monopolizing 50 or 100

individual trees, is likely to "own" a sample size

of trees large enough to reduce the effects of individual differences in productivity (of cones and

Peridermium) between trees. In other words, productivity, or the number of cones and/or Peridermium growths per unit area on the individual's

territory, probably closely approximates the average productivity per unit area calculated from the

total sampling area T.

If each territory contained only several trees,

then in many cases the productivity on the territory would deviate greatly from the average productivity of T. In other words, this means that a red

squirrel, by monopolizing a circular area of a size

approximating A, has a high probability of assuring

himself adequate resources and a healthy existence.

Having no reason to venture out of A because of

the absence of a payoff, the red squirrel remains in

his dominance arena and conforms to the nonoverlapping type of spatial system. Of course, if

total productivity varies from year to year, territory size and population density may vary accordingly.

Now I shall analyze the situation with chipmunks

First, since individuals do not inhabit mutually

exclusive and contiguous areas, I must approximate

A from density measurements on the study area (in

red squirrels, A was equal to the average territory

size measured for each habitat). This is done by

counting the number of utilized burrows on the

study area and dividing by the total area (T/N). I

used data from the spring of 1974 for this purpose.

A density of IS individuals for 2.066 acres (0.8S6

hectare) resulted in a calculated A of 0.16 acre

(0.065 hectare). This yields an average diameter (D)

of 28.7 m. Remember that the actual diameter (D)

is much larger than D (Figure 526). How does the

spatial distribution of the chipmunk'^ major food

resources compare to the calculated A or D?

Trout lily bulbs are very dense and homogeneously distributed across the habitat (see p. 81), such

that an area approximating A anywhere on the

study site would have a high probability of con-
102

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

taining the average density (calculated from the

total area T) of bulbs. The situation for beechnuts, however, is somewhat different. The spatial

availability of beechnuts is dependent upon the foraging mode employed by the chipmunks.

If chipmunks crown forage (see "Crown Foraging

versus Ground Foraging"), then the spatial availability of the nuts is a function of the location

and accessibility of the crowns (Figure 45). If the

chipmunks ground forage, then spatial patterning

of nuts is a function of the crown locations and the

nut dispersal pattern. Beechnuts tend to drop

straight down from the crown. Therefore, the seed

shadow for each tree is represented by the projection of the crown onto the ground and Figure 45

can be used as an estimate of resource patchiness.

Superimposing, at random locations, circles of

size A (D = 28.6 m or 94 ft) on Figure 45 reveals that

a maximum of around 12 beech crowns would be

included in A, the average number of crowns per

area A being 6.0. This contrasts sharply with the

situation described for red squirrels, where territories of sizes approximating A contain 50 or more

individual trees that vary in productivity levels.

The effect this has on chipmunks is as follows. If

variability in production exists between trees, then

a sample size of around six trees within an average

area of A may not appreciably buffer the effects of

variability. Furthermore, heterogeneity derived

from slight clumping of beech trees in certain

areas (Figure 45) may result in some home ranges

of size A that contain only two or three trees. This

leaves the individual at the mercy of the productivity levels of his few trees.

Obviously, it would be advantageous for most

chipmunk individuals to partake in excursions out

of A, the payoff being the location of concentrated

resource patches exceeding concentrations in their

own home areas. Of course, movements would be

restricted, so that the central area and food cache

are still adequately defended. Thus, individuals

must fight two opposing tendencies: one for adequately defending the central or core area, and the

other for increasing the sample of size of trees to

reduce the detrimental effects of variability in production between trees and density changes across

the habitat. By adopting an actual home range

diameter (D) of 60 to 90 m through trespass into

other core areas, an individual increases his actual

utilized area to encompass 30 or more beech trees.

This is probably a large enough sample size to

buffer the effects of density changes across the habitat and variability in production levels between

individual trees.

The situation with sugar maple seeds is more

complicated. I will not analyze it in detail since

beechnuts were the preferred food item during the

autumn, even when sugar maple seeds were available in abundance (see "Autumn Foraging"). Analysis of Figure 46 indicates that individual trees

are not densely distributed, and, on the average,

an area of the size of A would contain only two

crowns. However, sugar maple seeds are wind dispersed, such that the seed shadows of individual

trees are larger than the crown projections indicated in Figure 46. This tends to buffer the effects

of low densities of trees and variability in production between trees. However, some patchiness does

occur, seeds being concentrated under the crowns

of productive trees and under the groupings of

trees evident from Figure 46. It is my opinion that

the spatial distribution of sugar maple seeds is

similar in many respects to the situation I have

described for beechnuts such that the distribution

of this resource also encourages the overlapping

home range system.

The spatial patterning of red maple seeds is even

more patchy. Only five canopy-sized trees were on

the study area (Table 19), so most areas of size A

would contain no trees at all and P would be very

low indeed. This resource could only be intercepted

by most individuals if a widely overlapping home

range system is employed. It is possible that if red

maple were the only critical resource, chipmunks

would find it hard to maintain a sedentary and

solitary mode of life in the hardwoods.

In conclusion, the chipmunk data indicate that

the patterning of the critical resources conform to

the expectations generated by my argument, where

P is low and the individual finds it to his advantage to make periodic movements out of his dominance arena (A) in order to exploit resource

patches.

Observational data of actual foraging by chipmunks supports my contentions. I noted numerous

examples of the location of high productivity beech

trees in the peripheral areas of "normal" home

ranges (Figure 12) during the height of the nut
NUMBER 265

103

season in the autumn. Further, I verified longer

movements of around 60 m from the home burrow

to individual beech trees dropping beechnuts prematurely (p. 76). In addition, I observed very long

distance excursions to a single red maple tree that

produced an abundant seed crop during one summer. Thus, individuals that locate such concentrated food resources receive an obvious payoff:

more seeds. Since long movements involve subordinance while trespassing through other individuals'

core areas, I postulate that in chipmunks the motivation to trespass and risk being chased is high.

In red squirrels, the motivation to venture into

other territories under normal conditions is probably much lower.

A problem I have not expanded upon in this discussion is "defendability" of areas in space by individuals (Brown, 1964). Motivations to trespass

are probably partially dependent upon the efficiency with which residents can locate, travel to,

and aggressively confront intruders. Data on the

efficiency of defense in red squirrels and chipmunks

are not available. The situation in red squirrels is

complicated by the existence of territorial calls

that advertize an individual's location and presumably help to repel intruders (Smith, 1968:34-

35). General observations on chipmunks in the

Adirondacks, however, prove helpful.

If an individual chipmunk restricted his movements to a circular area of around 30 m diameter

at the hardwood study site, it is apparent that the

majority of the intruders into his area could be

spotted or at least heard by the resident (remember that the study habitat was relatively free of

undergrowth; p. 67). Of course, by making longer

movements and spending time out of the core area,

the resident forfeits efficiency of defense. It would

appear, therefore, that there are no obvious environmental (aspects of habitat structure reducing visibility or masking auditory cues) or physical (abilities of the individual to locate, travel to, and expel

an intruder) restrictions on the adoption of a territorial mode of spatial organization by chipmunks,

if the diameter of the territories approximated the

calculated A (D = 28.6 m or 94 ft). Thus, the overlapping mode of spatial organization is best viewed

as a response toward other factors, such as the

spatial and temporal fluctuations in food resource

availability.

If spatial heterogeneity of food resources is correlated with the spatial patterning of individuals

in the population, then two approaches are available to test for the causative role of resource heterogeneity in the correlation. First, by artificially manipulating resource patterns, changes in spacing of

individuals may be invoked. This experiment, however, rests on the assumption that individuals

within the population can adapt to new conditions

over a short period of time. As pointed out by

Slobodkin (1968:193), this may not be the case.

Adaptation can occur at different levels. Some

adaptation is short term behavioral response of individuals. Physiological adaptations by individuals

may occur over longer time intervals. Responses

of the population through selective mortality and

fecundity (eventually involving genetic changes)

are of a very long term nature. Thus, if elements

of the motivation to trespass are genetically programmed, the population would be resistant to

short term changes induced by habitat manipulation.

A second approach is more adequate for shortterm study. An investigator can study a single animal species inhabiting several habitats that differ

radically in resource heterogeneity. Supposedly,

these different populations have had time to adapt

to their respective habitats over long periods (assuming resource heterogeneity remained relatively

constant through the time period). If the levels of

gene flow between the habitats is low, then specific

adaptations are even more feasible.

Neither type of approach has been applied to

chipmunks, but some data are available on red

squirrels with regard to the second approach.

Smith's studies (1968) of red squirrels in coniferous

forests in the Northwest and my own studies of red

squirrels in Adirondack coniferous forests (unpublished data) have indicated the existence of a nonoverlapping and contiguous territorial mode of

spacing. Layne (1954) studied red squirrels in hardwood forests at Ithaca, New York. Layne did not

find the species to be obviously territorial in that

habitat. He noted cases of toleration between individuals and did not recognize the territorial significance of some vocalizations that Smith (1968:

34-*-35) found correlated with territoriality. In addition, Layne provided evidence for overlap in use

of space by individuals.
104 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Perhaps a study of food types and their spatial

heterogeneity at Ithaca would reveal levels of heterogeneity or patchiness much greater than in coniferous forests, thus increasing the need for long

movements and home range overlap. Increased

movements out of core areas might result in lowered efficiency of defense of the core area, leading

to a degeneration of the effectiveness of the red

squirrel's conspicuous territorial call in repelling intruders. Territorial calls probably cannot function

in repelling intruders unless they are periodically

backed by adequate territorial defense. Heterogeneity in the spatial patterning of food resources at

Ithaca is indicated by the large number of nut and

seed producing tree species that Layne mentions

are utilized by red squirrels in his area.

Further studies of chipmunks and other sciurids,

designed to correlate spacing with spatial and temporal patterning of food resources, are needed to

test the validity of the hypotheses presented here.
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elements, follow the format of the series for which the manuscript is intended.

Legends for illustrations must not be attached to the art nor included within the text but

must be submitted at the end of the manuscript—with as many legends typed, doublespaced, to a page as convenient.

Illustrations must not be included within the manuscript but must be submitted separately as original art (not copies). All illustrations (photographs, line drawings, maps, etc.)

can be intermixed throughout the printed text. They should be termed Figures and should

be numbered consecutively. If several "figures" are treated as components of a single larger

figure, they should be designated by lowercase italic letters (underlined in copy) on the illustration, in the legend, and in text references: "Figure 9JD." If illustrations are intended to be

printed separately on coated stock following the text, they should be termed Plates and any

components should be lettered as in figures: "Plate 9b_." Keys to any symbols within an

illustration should appear on the art and not in the legend.

A few points of style: (1) Do not use periods after such abbreviations as "mm, ft,

yds, USNM, NNE, AM, BC." (2) Use hyphens in spelled-out fractions: "two-thirds." (3)

Spell out numbers "one" through "nine" in expository text, but use numerals in all other

cases if possible. (4) Use the metric system of measurement, where possible, instead of

the English system. (5) Use the decimal system, where possible, in place of fractions.

(6) Use day/month/year sequence for dates: "9 April 1976." (7) For months in tabular listings or data sections, use three-letter abbreviations with no periods: "Jan, Mar, Jun," etc.

Arrange and paginate sequentially EVERY sheet of manuscript—including ALL front

matter and ALL legends, etc., at the back of the text—in the following order: (1) title page,

(2) abstract, (3) table of contents, (4) foreword and/or preface, (5) text, (6) appendixes,

(7) notes, (8) glossary, (9) bibliography, (10) index, (11) legends.
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