FOOD STORING AND RELATED BEHAVIOR OF RED SQUIRRELS IN INTERIOR ALASKA.

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ABSTRACf

The relationship of red squirrels' (Tamiasciurus hudsonicus preblei)

food storing habits and population size to the supply of white spruce

(Picea glauca) cones was studied as part of a continuing study conducted

near College, Alaska. Field study was conducted from August 24, 1967, to

February 13, 1968. Twenty-three middens were present on the 21 ha study

area; the mean distance between them was 68.6 m. Caching activity began

prior to August 24, and continued until October 10. The cones are har-

vested from a roughly circular area surrounding the midden, with 79% of

the cones being harvested from within 20 rn of the rnidden. The rate of

cone-caching activity was recorded and indicated that at this latitude,

tirne is not a limiting factor in the nurnber of cones cached in a season.

On six cene-production plots cones were counted on the trees, in

rniddens, and on the ground. The cone crop was estirnated to be 56,720 to

177,100 cones per ha. Estimates of cones harvested by squirrels ranged

from 10% to 69% of the crop, depending on daily cone consurnption rate

and variation in caching activity. In 1967 two ~quirrels may have stored

enough cones for two winters.

Population density was estirnated at one squirrel per 0.9 ha. Beyond

a certain minimum level of cone production, approxirnately 14,000 cones

per ha, population density on the study area appears lirnited by terri-

toriality and factors other than the current food supply. Territoriality

is important in rnaintaining food storage areas, and two territories were

0.57 and 0.36 ha. Territorial competition was active and constant during

the study; rapid changes in territory ownership occur in the event of

mortality of a squirrel. Sorne changes in territorial structure occurred

after the caching period ended.

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ACKNOWLEDGMENTS

Various people have contributed to this study with both suggestions

and field assistance. For their help I would like to sincerely thank the

following people:

Dr. Frederick C. Dean, Head, Department of Wi ldlife Management,

University of Alaska, for initiation of, and his many suggestions through-

out the study, and for critically reading the manuscript .

Dr. David R. Klein, Leader, Alaska Cooperative Wildlife Research

Unit, for critically reading the manuscript.

Dr. Brina Kessel, Dean, College of Biological Sciences and Renewable

Resources, for critically reading the manus cri pt.

David L. Chesemore, Research Assistant, Alaska Cooperative Wildlife

Research Unit, for his many suggestions and assistance in all aspects of

this study.

Richard Fleming, fellow student, for his generous help on the vege-

tative survey of the study area and ana1ysis of the data.

Special thanks to my wife for her able and enj oyable field assistance,

and especially for her efforts with the typewriter .

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TABLE OF CONTENTS

INTRODUCTION

STUDY AREA

METHODS

Determination of Cone Crop

Determination of Cone-harvesting Area

Collecting and Marking Squirrels

FOOD STORING

The Midden and Its Location

Harvest Area .

Caching Behavior

Cone Cutting . .

Rate of Caching Activity

Mushroom Storage

CONE CROP ANALYSIS

Cone Counts

Cone Production

Cone Harvest by Red Squirrels

POPULATION DENSITY

TERRITORIALITY .

Vocalization

Territorial Disputes

Territory Size .

Territory Change and Expansion

Territorial Boundaries ...

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Table

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LIST OF TABLES

Analysis of forest cover on the Bonanza Creek Study Area, utilizing Cottam and Curtis' (1956) point-centered quarter rnethod . . . Analysis of cone caching observations . . Accuracy of test counts of cones on trees

White spruce cone production and red squirrel harvesting data on Bonanza Creek Study Area .

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Figure

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LIST OF FIGURES

Bonanza Creek Study Area showing grid sections, distribution of tree cover, midden location, and location of cane-production plots . . . . . .

Deviation of spotting scope count from actual number of cones on felled trees ...... .

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INTRODUCTION

This study represents the continuation of two preceding studies

(Brink 1964; Smith, M. 1967) to determine the ecological relationship of

red squirrels (Tamiasciurus hudsonicus preblei)1 to the production and

supply of white spruce (Picea glauca) seed and the regeneration of white

spruce in interior Alaska. The study area was the same as that used by

M. Smith (1967) to facilitate direct comparisons of cone crop and

population size. Field work was conducted from August 24, 1967, to

February 13, 1968. The study was supported by the Department of Wildlife

Management and the Alaska Cooperative Wildlife Research Unit, University

of Alaska, College, Alaska.

To better understand the relationship of red squirrel cone utilization

to the available cone crop, various behavioral and ecological data

concerned with food storing were collected. Primary emphasis was placed

on determining the total cone crop and the proportion harvested by red

squirrels. Estimates were made of the length of time and the size of

cone crop needed by red squirrels to store an adequate supply of canes

for a win ter.

Territorial behavior was evident during the study, and the average

territory size on the study area was estimated.

lscientific names of mammals follow Hall and Kelson (1959) and those of plants follow Anderson (1959).

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STUDY AREA

The study area was located about 25 km southwest of College, Alaska,

in the Bonanza Creek Experimental Forest. Field work was lirnited to a

457 rn square (21 ha) plot established by M. Smith (1967). The study area

- was 1ocated on a south-facing slope of about 14% , in a mature stand of

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white spruce (Picea glauca). The spruce stand was interspersed with

locally abundant quaking aspen (Populus trernuloides), alder (Alnus crispa),

and paper birch (Betula resinifera = ~· papyrifera). Quaking aspen and

paper birch occur in blowdown-caused openings (Smith, M. 1967), while

alder occurs lower on the slope in areas of surface drainage.

The study area was dorninated by white spruce with paper birch,

quaking aspen, and alder locally abundant, as is shown in the cover-type

map (Fig. 1) .

A list of the major plant, bird, and rnarnrna1 species found in the

study area can be found in M. Smith (1967).

The hornogeneity and the density of the forest cover on the study

area is reflected in the data presented in Table 1. Based on its irnpor-

tance value (Curtis and Mclntosh 1951) of 213.9, white spruce is clearly

the dominant species on the area. Spruce is followed in decreasing

importance by paper birch, quaking aspen, and alder.

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Table 1. Analysis of forest cover on the Bonanza Creek Study Area, utilizing Cottam and Curtis' (1956) point-centered quarter method.

x No. trees Per cent Basal X basal Species in sample frequency area (cm2) distanceb area ~er

tree

Al nus crispa 7 4.7 464 66 3.99

Be tula resinifera 22 15.6 4,391 200 5.18

Pi ce a glauca 107 74.5 29,038 272 3.23

PoEulus tremuloides 8 5.6 1,946 243 2. 71

aMean individual basal area at BH on the study area = 248.9 cm2 .

bMean distance is the distance from the sample point to the nearest tree.

cMean area per tree on the study area = 12.38 m2.

dDensity = the number of trees per hectare.

-x Densityd

Importance are ac e Value

15.9 37 13.1

26.4 123 55.1

10.4 593 213.9

7.2 44 17.9

e For a discussion of Importance value, see Curtis and Mcintosh (1951). Calculated from a base value of 300.

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METHODS

The study area was divided into a grid having twenty-five 91 rn square

sections (Fig. 1). The section corners were marked with red and yellow

flagging so that the investigator could easily recognize his location .

Each of the 25 sections was further sub-di vided into nine sub-sections,

and the sub-section corners were also marked.

The trees in the study area were measured by the point-centered

quarter method (Cottam and Curtis 1956). Each section corner was a

sample point yielding a total of 36 sample points. Quantitative tree

data were transferred onto IBM punch cards. Frequency, basal area, mean

area per individual tree, and density were computed on an IBM 360 digital

computer using a FORTRAN IV program written by Richard Fleming, University

of Alaska; the results are shown in Table 1.

For the purpose of this study, the term midden refers to a large

accumulation of cone bracts and stripped cone stalks underlain by an

elaborate system of tunnels. On the study area the majority of cones

stored by squirrels were stored in caches dug in the midden. Pruitt and

Lucier (1958) refer to these as "kitchen middens." In addition to kitchen

middens, there were also many smaller cone storage areas throughout the

study area, containing about 10 to 20 cones in small depressions in the

moss, and these are also referred to as caches.

The study area was systematically searched for middens and each

midden was marked with orange timber-marking tape and plotted on a map

of the grid (Fig. 1). Recause more middens were progressively found

throughout the fall, the grid was traversed along different routes to

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increase the possibility of finding additional middens. The middens were

- repeatedly checked for squirrel activity. From August 24 through October, the study area was visited almost

daily. The degree of activity was noted by recording the number of red

squirrels observed and the frequency of territorial calls. All behavior

Each midden was numbered according to the sub-section in which it

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pertinent to the study was recorded.

- was located. For instance, the midden located in the center of section 12 was numbered 12C (Fig. 1). The squirrels observed were likewise

identified according to the midden within their territory. Two middens

located off the study area, but involved in the study were numbered C-1 ·~ and C-2.

The degree of activity on a midden was determined by severa!

criteria: (i) the general activity of the squirrel that defended the

midden; (ii) the number of newly eut cones in the midden; (iii) the

amount of fresh digging on the bract pile on the midden. During the

winter, the degree of activity on a midden was easily determined from

the amount of cone bracts and stripped cone stalks lying on the midden

and from the tracks in the snow leading to the entrance tunnels on the

middens.

To determine the amount of cone cutting activity, 10 ground tran-

sects, 50 rn by 1 rn, were randomly located and established throughout the

study area. Initially all cones were removed from the transects; and,

subsequently, every two days the number of new cones lying on the ground

within the transects was counted and removed. Since these counts were

made every two days, the daily cane-cutting activity was not measured.

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However, the counts illustrated a general trend in cutting activity.

Determination of Cone Crop

To determine the per cent of the cone crop harvested by red squirrels,

sorne method of determining the total cone crop on the study area had to

be devised. Six cone-production plots were established, three having ac-

tive middens within their boundaries and three not having middens. The

plots were circular, with a diameter of 40 m. In the three plots having

middens, the center of the midden was chosen as the plot center, and the

three plots lacking a midden were established from sub-section corners.

The plots were randomly located by assigning numbers to middens and grid

subsection corners and selecting numbers from a random number table.

Because cone production was observed to be restricted to trees with

a DBH of more than 15 cm, all white spruce larger than DBH of 15 cm were

classed as potential cone-producing trees. Each potential cone-producing

tree was marked permanently with metal tags so that cone production

comparisons can be made in future years. To compare plots having middens

to those not having middens, the number of potential cone-producing trees

was counted and the total basal area of the potential cone-producing

trees was calculated on each plot.

After cone cutting by red squirrels had ceased, tluee cone counts .1

were made on each plot: a count of the cones on the trees, cones lying ~}

on the ground, and cones in each midden on the three plots having middens.

The cones on trees were counted from the ground with a 20X spotting

scope. Before the tree cone count was attempted on the plots, 10 test

counts were made on trees off the study area. For each test count, the

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cones were first counted from the ground; then, the tree was felled and

the actual number of cones was counted to determine the accuracy of

counting with the spotting scope.

In an attempt to get more accurate counts, severa! photos of tree

crowns were taken with a 35mm camera using a 300mm lens. The slides were

projected on a screen divided into a grid to determine whether accurate

counts could be made using this method. However, because of frequent

poor light conditions and a lack of clarity in the slides, no greater

accuracy could be attained using this method than with the 20X spotting

scope.

To facilitate counting the cones on the ground in each cone-

production plot, a 40 rn square plot was superimposed on the circular cone-

production plot. The 40 rn square plot had an identical center with the

cane-production plot. The 40 rn square plot was divided into 100,4 rn

square sample plots, which were numbered consecutively. A random number

table was then used to select 10 sample plots in which to count cones.

Each sample plot in the square was eligible regardless of its location

in the circular cane-production plot. The number of cones in the 10

sample plots was then extrapolated to calculate the number of canes on

the ground in the 40 rn square plot and reduced accordingly for the total

number of cones in the circular cane-production plot. The number of

cones lying on the ground was counted separately from the number of cones

in the midden on each plot.

The number of cones in the middens was counted by excavating the

middens by hand and counting the cones.

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Determination of Cone Harvesting Area

In order to determine the size of a squirrel's cone-harvesting area,

on each of the three plots having a midden, various distances up to 40 rn

were measured from the center of the midden outward and marked on trees

as reference points. When squirrels were observed carrying cones into

their middens, the point where the squirrel picked up the cone was noted

and the distance from the midden estimated on the basis of the marked

trees. The number of cones hauled per trip and the time required to make

the haul were also noted in many of the observations.

Collecting and Marking Squirrels

Attempts were made to mark squirrels with a Nel-Spot "707" pellet

pistol. The paint pellets were sufficient for marking the squirrels by

hitting a tree or log very close to the squirrel at the proper angle so

the paint would splatter on the squirrel. However, from field observations

and tests on a captive squirre 1, i t was found th at the paint would be vis-

ible on the fur of the squirrel for no longer than 24 to 72 hours.

National live traps were used for trapping squirrels on the study

area, and Nyanzol "A" fur dye was used for marking the captured squirrels.

Fitzwater's (1941) formula was modified for longer dye stability. Two

grams of the dye were dissolved in 100 ml of tap water, and only 3 or 4

ml of hydrogen peroxide (10 volume) was used. After being shaken

vigorously, it was allowed to stand for at !east 8 hours. Such a mixture

remained useable for up to 4 days. Cotton swabs were used for applying

dye, and various patterns were employed to aid in field identification

and differentiation.

Red squirrels were also marked with number 1 Monel fingerling tags

placed on the outer fringe of the ear near the base. To further aid in

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field identification a loop of colored, plastic-coated bell wire (1.3 cm

diameter) was inserted under the Monel tag before it was clamped on the

ear. These bell-wire tags were visible for up to 15 rn in the field.

Halvorson (1963) first used electrical wire ear tags as an effective

means for identifying squirrels in the field.

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FOOD STORING -- In interior Alaska, the red squirrel's diet consists largely of

conifer seeds (Dice 1921, Murie 1927, Brink 1964, Smith, M. 1967). This

dependence on a single food source appears to be the reason for the

harvesting and storing habits of the red squirre1 and the defense of its

storage area (Smith, C. 1963).

The red squirrel is bath energetic and persistent when storing food

for the winter. There are numerous reports of squirrels storing large

amounts of readily available food in a relatively short period of time.

Murie (1927) cited a cache discovered by Otto Geist in an abandoned cabin

in which within 3 weeks, a red squirrel cached about 2 bushels of high-

bush cranberries (Viburnum edule), 2 bushels of aider canes, and nearly

1 bushel of cow-parsnip seeds (Heracleum lanatum) .

Squirrels often store a wide variety of food items. Seton (1929)

ci tes instances of red squirrels storing potatoes in robins' nests.

He mentions that squirrels usually store soft or perishable food in - trees, and hard, durable food is buried or stored in hoards or caches. Food storing by red squirrels seems more prevalent in the northern

latitudes of its range than in the southern latitudes (Osgood 1900, Dice

1921, Murie 1927, Seton 1929, Layne 1954, Hazard 1960, Smith, M. 1967).

Hatt (1943) found that red squirrels in New York rarely stored food in

middens, but in interior Alaska, storage of food appears to be almost

entirely in caches on the middens.

C. Smith (1963) discusses the evolution of food storing by red

squirrels. He states that it appears that their harvesting and storing

habits have evolved to result in the collection of conifer cones before

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they 1ose their seeds, and the storage of the cones in damp places so

the seeds will remain in the cones until they are eaten. With the severe

winters in interior Alaska, red squirrels probably could not utilize

conifer seeds without this habit, because deep snow and frozen ground

would prevent them from retrieving widely scattered individually stored

cones, or scattered individual seeds in an efficient manner.

Food storing appears to be an innate characteristic in red squirrels.

Layne (1954) observed young squirrels, a few days after weaning, attempting

to hide food, and Hazard (1960) observed captive squirrels, isolated

since a young age, storing food.

M. Smith (1967) stated that cutting and storing activity by red

squirrels in interior Alaska begins between August 1 and 15, while Dice

(1921) first observed cutting and storing in interior Alaska on September

6. In 1967 the study area was not visited until August 24. At this time

few freshly eut cones were observed, and it appeared that cone cutting

and caching had just begun. On September 3 caching activity reached a

peak and until September 16 was vigorous, and with little daily fluc-

tuation except during periods of heavy rainfall or snow when caching

activity ceased. After September 16 a decline in caching activity became

noticeable.

M. Smith (1967), in persona! communication with Robert Gregory

(Research Forester, U. S. Forest Service), learned that in interior

Alaska white spruce seed usually matures and begins to fall about August

20, and at least 50% falls by September 15. The investigator, during

this study, first observed seeds falling on September 14, and inspection

of cones lying on the ground on this date indicated that many of the

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cones were open and had already shed sorne of their seeds.

By October 10, caching activity had for the most part ended. Caching

after October 10, and until the first snowfa11 on October 17, consisted

of activity on and close to the middens, in which cones were moved from

the perimeter of the midden to its center. Generally, it appeared that

the squirrels were attempting to decrease the perimeter of their midden

and concentrate the cones into a smaller area.

The Midden and Its Location

Cone storage middens are conspicuous in spruce forests of interior

Alaska. On the Bonanza Creek study area many middens had large bract

piles, dotted with numerous entrance tunnels to the underground tunnel

system. These large middens appeared to be the center of vigorous

squirrel activity and perhaps were established for a long period of

time. They contrasted with smaller middens also present in the study

area that were lacking the degree of activity observed in the larger

middens. The middens were variable in size, but sorne were as large

as 75m2, and the smaller middens were about 30m2. The importance of

the smaller middens is not known, but they may represent ownership by

young squirrels and perhaps are only active during years of cone ahun-

dance. The three middens excavated during this study were 75 m2, 50 m2,

and 58 m2 . Sorne of the midden sizes reported in the literature are as

follows: Osgood (1900) observed a midden in Alaska of 122m2 (400 ft 2);

Hatt (1929), in the few middens he observed, estimated sizes of 107m2

(350 ft2) and 47.5 m2 (156 ft2); and Brink (1964:50) estimated the average

size of the larger middens on his study area near Fairbanks, Alaska, to

be " a few meters in diameter."

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The middens on the study area were comprised of cone bracts approx-

imately 20 cm deep on top of mineral soil. Under the bract pile was an

elaborate system of tunnels that the squirrel used for sorne cone storage

and shelter in the winter. In October and November, squirrels were

observed hauling dry grass and beard lichen (Parmelia ~·) to bath the ir

middens and tree nests. This behavior may suggest that squirrels use

both tree nests and their middens for shelter during the winter. The

use of underground midden nests is well substantiated in the literature.

Shaw (1936) found that western pine squirrels (!. È.· fremonti) used brush

piles for shelter and suggested that they lived at least part of the

winter underground. Soper (1942) also concluded that red squirrels spend

more time underground than in tree nests during the winter, and Murie

(1927) concluded that the ground burrows were for refuge during the winter.

In New York, Petrides (1941) found that red squirrels excavated snow

burrows to reach food sources above the ground. Pruitt and Lucier (1958)

during a 3-year study near Fairbanks, Alaska, found that red squirrels

live in extensive burrows under their middens during the winter.

Midden location may be influenced by many factors: moisture, humidity,

soil type, proximity to nesting sites, availability of escape routes and

pathways for travel, and food supp ly.

Most of the middens on the study area were located adjacent to logs

and fallen trees, but a few were in relatively open areas. Hatt (1943),

in Colorado, found that pine squirrel middens were usually centered about

a tree or cluster of trees, or about a stump or log.

Middens on the Bonanza Creek study area appear to be uniformly

scattered. The map of cover-type (Fig. 1) illustrates the mixed forest "Î

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cover on the study area in relation to midden distribution, the majority

of the are a being a homogeneous stand of white spruce.

It is interesting to note that only two middens were located within

a mixed stand. Both of the middens (6SE and 17E) were srnall rniddens and

may have been active only periodically.

Layne (1954) suggested that food supply may influence the shape and

size of the home range of red squirrels and rnight induce a shift of horne

range. Red squirrels have been observed emigrating from areas of food

scarcity to areas of food abundance (Brink 1964, Smith, C. 1965, Smith, M.

1967). It follows that rnidden location could also be related to food

supply. On each of the plots, the nurnber of cone-producing trees (DBH of

15 cm or more) was counted. The plots having middens had significantly

more (P=.01) cone-producing trees than those without rniddens. Accordingly,

the basal area was significantly greater (P=.001) on the plots having

rniddens. Although this represents the tree density surrounding only three

of the 23 middens on the study area, it may suggest that a greater

nurnber of trees could supply a greater number of cones for a squirrel in

an area close to its rnidden, and possibly enhances its food storing cap-

abilities. Accordingly, perhaps the most efficient means of gathering

cones is for the squirrel to gather all the cones in trees nearest the

rnidden, thus rninirnizing the distance cones would have ~o be carried.

The locations of rniddens on the study area may be the result of

territorial tolerance. This territorial tolerance would be dependent on

the available food supply, as C. Smith (1965:135) found that territory

size is " ... inversely proportional to the physical availabili ty of food

per acre of forest." This observation may exp lain the territorial

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location, and perhaps conditions more closely related to the microhabitat

would govern the location of the middens within the territory.

Shaw (1936) pointed out the need for moisture in cone storage areas.

He studied the western pine squirrel in Idaho and found most of the

middens in swampy or marshy areas and two middens in "spring-ooze" areas

in which sorne cones were completely submerged. By keeping cones in a

closed condition in water for up to 3 years, Shaw demonstrated that mois-

ture keeps the cones closed and thus prevents the loss of the seeds.

There were several seepage areas on the Bonanza Creek study area, but no

stored cones were found in or near them. However, due to the heavy moss

layer, soil texture, and climatic factors within the Bonanza Creek spruce

forest, a great deal of moisture was prevalent in the moss throughout

the entire study area. Perhaps seepage areas were used for storage in

Idaho due to an overall shortage of moisture in the environment. When

excavating three middens, the investigator found that ali the stored

cones were moist, except for a few cones lying loose on the surface of

the midden. White spruce cones taken from the middens and air-dryed,

opened and the seeds readily feil out.

Moisture is not always a prerequisite for cone storage as red

squirrels have been observed caching cones on tree limbs (Clarke 1939).

If this type of storage results in the drying and opening of the cones

and the subsequent loss of seeds, this storage method would represent

wasted effort on the squirrel's part. However, this method may have

been only a temporary means of storage as the squirrels may not have

relied on these cones as a food source for the winter, and instead,

consumed them shortly after storage.

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Because of the terrain and the tree cover on the Bonanza Creek study

area, the distance between various middens was often difficult to realize

without reference to the grid map. The mean distance between middens

was calculated from the distances from each midden to the two closest

neighboring middens. The mean distance was 68.6 + 7.9 rn (P=.05). The

shortest distance between neighboring middens was 31 rn and the longest

distance was 146 m.

Harvest Area

The area from which squirrels harvested cones appeared to be roughly

a circular area. This observation agrees with C. Smith's (1963:57)

conclusion: "The most efficient me ans of storing and defending conifer

cones and fungi is for each individual to harvest all the cones and fungi

in a circular are a and carry them to a central location for defense."

The size of the area from which red squirrels were harvesting cones

was of interest in determining the total cone production on the study

area. The analysis of the cone caching observations shows that 79% of

the cones cached were harvested within 20 rn of the midden (Table 2).

Caching Behavior

The red squirrels observed during this study were meticulous in

depositing cones in their middens. They always had an excess of holes

dug in the loose bracts on the midden. The holes sometimes opened into

one of the tunnels under the midden, but usually the holes were shallow

(at most 25 cm deep) and did not join the tunnel system.

The squirrels always transported cones with the base of the cone in

their mouth, and always packed the cones tightly and tip-down in the holes.

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Table 2. Analysis of measured cone caching observations.

Distance of trip in meters

0 - 10

11 - 20

21 - 30

over 30

Totals

Number of

trips

101

83

45

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233

Number of cones hauled

125

104

52

4

285

Per cent of trips

absolute cumulative

43% 43%

36% 79%

19% 98%

2% lOO%

Per cent of cones hauled

absolute cumulative

45% 45%

36% 81%

18% 99%

1% 100%

' - -· ~-·-~ .. ··--~--~----------·------"

'

..... 00

"~------

19

Hatt (1943: 340) stated, " ... typically, these pockets are numerous in a

small area and each contain 6 to 30 or more cones, tightly packed."

Three rniddens were excavated on the study are~ and the investigator found

the cones so tight1y packed that it was often difficult to remove them

from the holes by hand.

Sorne of the cone-filled holes were covered by bracts, but the

majority were not covered. It appeared that the squirrels made no

atternpt to actually conceal or cover the cones, but that the covering was

the result of the squirrel's digging additional holes in the midden, and

in the process, the excavated bracts would accidently cover cones

previously stored.

Many of the cones harvested by the squirrels were stored throughout

their territory in scattered caches of 6 to 15 cones, usually in depres-

sions in the moss layer. One squirrel on the study area cached up to 15

cones in a depression caused by a footprint in the moss left by the

observer. Hatt (1943) also found cones stored in small pockets in the

forest floor.

The importance of these small caches is questionable. However, on

the Bonanza Creek study area, these cones were tightly packed and very

moist and probably would be preserved as effectively as those cones

stored in the midden. Layne (1954) observed similar habits in red

squirrels in New York, which buried nuts usually in clusters in a shallow

depression of soil beneath the leaf mold.

Throughout the fall, red squirrels utilized cones from these small

storage caches and seldom fed on the midden proper. This behavior

continued until mid-December when tracks in the snow indicated

20

that squirrels began feeding entirely from canes stored on their rniddens.

This marked change in feeding habits may be related to the increasing

snow depth (20 cm at the time), decreasing daily temperatures, or the

frozen condition of the ground.

Cone Cutting

During the study, squirrels were frequently observed cutting cones.

Cutting activity was readily detected from the sound of cones hitting

logs and other abjects as they were dropping to the ground.

During this study, no squirrels were observed cutting steadily for

longer than 6 minutes. Dice (1921:25), who observed a squirrel cutting

cones in interior Alaska, noted that it worked continuously for 15 min-

utes, and said: "Cones were thrown away from the tree by a backward

toss of his head and fell in all directions."

Rarely did squirrels haul freshly eut cones to their middens. After

every observation of cutting, the squirrel began caching cones from a

different location on his territory.

The rate of cutting was not recorded, but Dice (1921) observed a

squirrel cutting at a maximum rate of one cone per second. Even if the

rate was much slower, perhaps only one cone per 5 seconds, at least 720

cones could be eut in one hour. At this rate it would only require 28

hours to eut more than 20,000 cones. From the abundance of uncached

cones on the ground during the caching period, it appeared that the

squirrels eut cones at a rate in excess of the rate at which they were

cached.

When cutting and caching activity had ended for the season, it was

apparent that not all of the eut cones had been stored in rniddens, for

21

many were lying on the ground throughout the study area. Table 3 in the

Cone Crop Analysis section shows that in plots I, II, and III, only 55%,

24%, and 68%, respectively, of the cones eut on those plots, were stored

in middens.

The ten 50 rn by 1 rn ground transects showed a steady decline in the

number of eut cones from September 12 to 30 and a slight rise in number

of cones between September 30 and October 4. After October 4 no cutting

was observed.

Rate of Caching Activity

While cutting and hauling cones, red squirrels appeared energetic

and absorbed in their activity. They usually ran along logs while

retrieving a cone, or, in the absence of logs, would follow the same route

frequently enough to form a distinct path in the moss layer. Even though

distinct routes were frequently used, squirrels deviated enough to gather

cones uniformly from the entire are a surrounding their middens.

During the caching period, individual squirrels showed a high degree

of variation in persistence of caching activity. Squirrels 9SE and 12C

were particularly industrious and seemed to work for longer periods of

time than other squirrels. They were both observed caching cones quite

steadily for up to 1 hour. Squirrels lOS and 16NW were watched frequently,

but seldom cached cones in their middens for more than severa! minutes

at a time. This variation in activity was clearly illustrated in the

resultant size of their middens and in the defense of their territories.

Middens 12C and 9SE had 12,855 and 13,965 cones respectively, and midden

16NW had only 2,421 cones. Squirrels 12C and 9SE were very active and

successful in defending their territories, while squirrel lOS lost his

1

1

22

territory, to squirrel 9SE.

Occasionally red squirrels eut a branch tip containing more than one

cone. They would then haul the small branchlet to their midden with the

cones intact. Red squirrels were observed hauling more than one cone

during only 23 of the 233 measured observations. On these 23 occurrences

a total of 75 cones was hauled. The greatest number of cones that were

observed being hauled by a squirre 1 at one ti me was fi ve, but a bun ch of

six cones was found lying on midden 12C. Twelve of the 23 trips with

more than one cone were from 0 to 10 rn away from the rnidden, nine from

11 rn to 20 rn, and two of the trips were from 21 rn to 30 m. No observed

trips with more than one cone were made from farther than 30 rn from the

midden.

To determine the rate at which squirrels cache cones, I timed 130

observations of squirrels hauling cones to their middens. The distance

the squirrel traveled from the rnidden to the cone it retrieved was noted

as well as the elapsed tirne of the round trip. Each trip was timed from

the moment the squirrel left the midden until it returned and deposited

a cone in its midden. For these measured trips, the mean distance was

13.6 ± 1.02 rn (P=.OS) and mean time for the round trip was 32.2 ± 3.8

seconds (P=.OS). Therefore, during the measured trips the squirrels

observed traveled at a rate of 2.36 ± .10 rn per second which included

fin ding a cone.

During the cone caching period in interior Alaska (August 1 to October

1), day-length decreased from 18 to 11 hours. If a red squirrel spent

10 hours a day caching cones, with the observed mean time per trip of 32

seconds, it could cache a maximum of 1,125 cones per day. In 3 weeks a

23

squirrel _could cache 23,625 cones, and it would travel about 321 km (200

miles). A more conservative estimate of 6 hours of caching activity per

day would require 30 days to cache 20,000 or more cones. It is apparent

that during a year of cone abundance, time is not a limiting factor in

the number of cones a squirrel is able to cache in a season.

Squirrels frequently would terminate their caching activity and eat

a cone, or ascend a tree and remain out of sight of the observer. More

long-term intensive observations of red squirrel behavior would be

needed to determine accurately the amount of time spent daily, eating,

resting, and engaging in other activities.

Mushroom Storage

· Squirrels were observed storing mushrooms on fLve .occasions during

the fall of 1967. M. Smith (1967) found that mushrooms were frequently

utilized by red squirrels on the Bonanza Creek study area during the fall

of 1964, when cones were scarce, and they became the most impor~ant

source of food in late spring, 1965, when the cone supply on the study

area became depleted.

Smith reported finding 24 mushrooms on the branches of three white

spruce near a midden. No similar concentration of stored mushrooms was

found during this study; only single mushrooms were found on any one

tree.

~

J(

~·i : ~

1

ît" r

CONE CROP ANALYSIS

The 1967 cane crop on the study area was first rated by using a 10-

category crop rating system devised by Werner (1964). The cane crop

was numerically rated "S" (few canes on 50% of the trees, many cones on

occasional trees). M. Smith (1967) rated the cone crops: "2" (few canes

on occasional trees) in 1964 and "l" (no cones on any trees)" in 1965,

two successive years of cone crop failure on the Bonanza Creek study area.

No estimate for 1966 is available, but the cone crop was reportedly

greater than in 1965.

Cone Counts

There have been severa! attempts to assess cone production by counting

canes on trees; most of the methods rely on sample counts of marked

branches as an index of the cone crop (Winjum and Johnson 1962). In

this study, however, an attempt was made to count the entire cone crop

on the trees in the established cane-production plots, by counting every

cone.

As described in the Methods section, the accuracy with which the canes

on the trees could be counted with a 20X spotting scope was tested. The

data from the test counts are presented in Table 3. The table shows that

the error in the count with the spotting scope decreased considerably

wi th experience. For the first fi ve test counts, the mean error was 32%,

while the mean error of test counts 4 through 10 was 18%, and of test

counts 6 through 10, 10%.

The error increased when counting larger numbers of canes (Fig. 2),

and it appeared that a combination of the number of canes counted and

24

·.f :t

' ;! 'J ,j ~1 J ~ ,j ·~

j 1 ~

~\~ i

r~ :,~

1

Table 3. Accuracy of test counts of canes on trees.

Test Total Count Actual Number Error, Number Per Cent Count with Scope of Canes of Canes Errorl

1 500 1,353 -853 63

2 625 527 + 98 18

3 800 798 + 2 00

4 500 935 -435 46

5 802 1,183 -381 32

~ 6 775 838 - 63 7 e; ~. ~ ~~ ·\ 7 1,150 1,122 - 72 6 t' ,, tr; ·~ ~

8 230 193 + 37 19

c 9 150 "'i:'

178 - 28 16 ......... ~.... . 10 126 124 + 2 2 ....... .. ;--- 1

- ' 1The absolute value of error was divided by the actual number of canes on the r , ·-' ~-... 1 •

)o ~! trees.

.. , MU &4tktŒ.:;: t:lfl;utz mn_IIJ . .l!!JI)!!WiA a.~~--'-~"_ .... ........,.,·

N U1

---- ... -· ·····----- ·:-::;::::::::;:;;;::;;;;;;;·-;;.;.··· ;.....;..--

2

' ! +

• 3 :

'

i 6

·, .. , -· ..... ...,.

•

• 4

• Ti =· !7 .

• 5

oouuoooooouo Deviation of .... i,. ICope c-nt fr- fellocl troe c-r .

• $pottine ICCipe C-' re411virM to e411UOI fellod ,,.. ,_,_

!

• ,.

o 100 200 300 400 eoo eoo 100 800 eoo 1000 1100 1200 aoo MOO FELLED TIEE COUNT

Figure 2. Deviation of spot ting scope count from actual number of canes on felled trees.

26

'' 1" i 1

experience was important in decreasing the error of the count with the

spotting scope.

27

The count of cones on trees (Table 4) was made after the caching

activity had ended and there were relatively few cones left on the trees.

Therefore, since the number of cones had decreased, and the investigator's

experience had increased, the error should have been kept at a minimum.

It was assumed, therefore, that the error was kept to a minimum of 10%

in the count of cones on the trees.

The count of cones lying on the ground in each plot was conducted as

described in the Methods section. This count included the cones lying

on the ground within the cene-production plot but not those cones which

were within the midden. The results of the ground cone count is pre-

sented in Table 4.

The cones in the middens on plots I through III 'were counted by

excavating the middens and counting the actual number of cones present

in the middens. In order to determine cone production within the 40 rn

diameter plot, it was necessary to subtract the estimated percent (20%)

of cones in the midden that were harvested from beyond the perimeter of

the plots. This per cent was determined from measured observations of

caching activity and is discussed in detail in the Food Storing section.

The results of the midden counts is shown in Table 4.

Cone Production

Since the error of the tree cone count decreased when counting

smaller numbers of cones and with experience, the variation would not

satisfy a normal distribution. Therefore, normal statistical theory

could not be used in analysis of the test counts. When considering the

"

Table 4. White spruce cone production and red squirrel harvesting data on Bonanza Creek Study Area.3

Number of cones on trees

Number of cones eut:

A. lying on the ground

B. in the midden

Minus % carried to midden from off the plot2

Number of cones in midden from plot

Total number of cones on plot

I

2 '741 to

3,349

9,344

13,965

-2,744

11,221

23,306 ·tO

23,914

II

4,545 to

5,555

6,060

2,421

-476

1,945

12,550 to

13,560

1There were no middens on plots IV, V, and VI.

Plot Number

III

3,749 to

4,581

4,895

12, 855

-2,526

10,329

18,973 to

19,805

IV

12,380 to

15, 130

3,244

1

15,624 to

18,374

v

4, 771 to

5,831

377

1

5,148 to

6,208

2The calculated per cent (19.6%) from observation of red squirrels hauling cones to middens.

3Not including the estimated number of cones eaten by red squirrels on the study area .

. ·~~, _. .. ~.J:"'.;~Jj~f§~·.;r" ~ :fÎ~l-~f-':i:--l

.. ;

...

29

error of 10% (the assumed error of the cone count of the trees) , the re-

sulting mean number of cones per plot for the six cane-production plots

ranged from 7,124 to 22,244 cones. Since this represents a random sample

of cone production on the study area, this mean was extrapolated to

calculate the estimate of 1,184,308 to 3,697,888 cones on the 21 ha study

are a.

Cone Harvest by Red Squirrels

The cone harvest on each plot was calculated by adding the total

number of cones in middens and on the ground surrounding middens, less

the number of cones brought in from outside the plot, to the total cone

consumption during the cone-caching period.

The wide variation in the number of cones counted in the three middens

that were excavated adds more variance to the estimate of the total number

of cones stored in middens on the study area. To be more realistic, the

mean number of cones in the middens on the plots I and III .[13,410 t 1,708

(P=.20~ was treated separately from the number of cones in the midden on

plot II (2,421 cones).

There was sorne variation in the characteristics of the middens on the

study area. On the basis of size, the amount of activity by the squirrel

defending the midden, the volume of accumulation of newly eut cones, and

the rate of accumulation of newly stored cones, the 23 middens on the

study area were classified into two groups: large, active middens similar

to those on plots I and III, and small, less active middens similar to

that on plot II. It was a relatively simple task to choose the large,

active middens; 14 were classified into this category. The midden on plot

II had a relatively small accumulation of cone bracts and it appeared to

t " ~~

....

30

be more recently established than the other nine smaller, less active

middens~ From its appearance, and the lack of squirrel activity on the

midden, I concluded that the 2,421 cones in the midden represented a

smaller number than was present in each of the other small middens.

Therefore, the average number of cones in these middens was estimated to

be between 3,000 and 5,000 cones. Accordingly, the calculated total

number of cones stored in middens on the study area was 190,828 to 256,652

cones (Appendix 1).

The number of uncached cones lying on the ground in the area sur-

rounding the midden represents a large part of the total harvest by red

squirrels in these plots. Prior to mid-December, the squirrels on the

study area fed very little on their middens, but foraged for cones in the

area surrounding their middens. Table 4 shows that in the three cone-

production plots having middens, there were 9,344, 6,060, and 4,895 cones,

respectively, on the ground within 20 rn of the middens. This constituted

39%, 40%, and 25% of the total number of cones on these plots. The mean

number of cones on the ground in the three plots was 6,766 ± 2,512 (P=.20)

cones. Assuming this number of cones represents a mean for the area

surrounding the 23 middens present on the study area, this would be a

total of 97,842 to 213,394 cones.

The number of cones eaten by red squirrels must also be considered

in calculating the total number of cones they harvest. Estimates range

from 40 to 50 per day (Brink and Dean 1966) to 156 cones per day (Smith, M.

1967). Brink based his estimates on the number of cones he found in middens

during the fa1l of 1962. M. Smith (1967) estimated 156 cones per day for

interior Alaska from daily calorie requirements of red squirrels calcu-

lated by C. Smith (1965) in British Columbia. Although daily cone

i 1 j

l ~

j 1

~

' l

~

...

....

._

31

consumption wou1d vary annually, depending on the amount of sound seed per

cone, the above two estimates were accepted in this study as estimates of

maximum and minimum winter daily cone consumption rates of red squirrels.

The date when red squirrels begin feeding on the new cone crop varies

annually, but is approximately August 1 (Nienstaedt 1957, Smith, M. 1967);

on October 5 the cone counts on the production plots on the Bonanza Creek

study area were finished which represented a period of 97 days. If a

maximum of 156 cones were eaten per day per squirrel, and 23 squirrels

were present on the study area, 348,536 cones would have been consumed

during this period. If a minimum of 40 cones per day were eaten during

this period 89,240 cones would have been consumed.

The total number of cones in middens and on the ground, and the total

consumption at a rate of 156 cones per day, adds up to a total harvest of

636,706 to 818,082 cones; and at a consumption rate of 40 cones per day,

377,910 to 559,286 cones. These totals represent a harvest of 17% to 69%

and 10% to 47%, respectively, of the total cone crop on the study area.

The cone-harvest calculation can be found in Appendix I.

This study and M. Smith's (1967) findings indicate that red squirrels

do not utilize all of the cones cached in their middens each year, but

that un-utilized cones accumulate in middens over several years. M. Smith

(1967) found that this accumulation was an important food source for

red squirrels during a year of cone crop failure .

The number of cones that a red squirrel consumes in one day varies

from year to year depending on the amount of sound seed in the cones for

that year (Smith, M. 1967). This variation makes it difficult to estimate

the rate of cone consumption, and accordingly, the rate of accumulation

. ..,,

-

--

-

32

of un-utilized cones in middens.

1 f one assumes that 40 cones per day are consumed by a red squirrel

during the winter (Brink and Dean 1966), then from October 15 to July 15,

the period when squirrels would be utilizing cached cones to a large

degree, 10,880 cones would be utilized per squirrel during this period.

Based on these data the squirrels on plots 1 and Ill should have had more

than enough cones in their middens to supply them with food during the

winter of 1967-1968.

However, if the squirrels utilize all of the cones lying on the

- ground within 20 rn of their middens, the total number of cones available

'-

·-

....

.....

._

....

...

....

to them would increase considerably. For instance, squirrel 16NW on plot

II cached only 2,421 cones in his midden but would have had 8,481 cones

available if he utilized the cones on the ground. If the cones on the

ground were added to the number of cones in the middens on plots 1 and

III, 22,310 and 17,750 cones, respectively, would have been available to

the squirrels on these plots.

Sin ce it was calcul ated ab ove th at at a consumption rate of 40 cones

per day about 10,880 cones would be utilized from a midden during the

winter and early summer, it appears that plots 1 and Ill contained almost

twice as many cones than were required for one year. It appears that from

one year of caching, the squirrels on plots 1 and III would have had a

surplus of cones nearly adequate to last through one year of cone crop

failure. Squirrel 16NW, however, would have only enough cones to last

one winter at the most; and if a year of cone crop failure followed, that

midden would probably be abandoned .

If the daily cone consumption rate was as much as 156 cones during

33

1 - the period from October 15 to July 15, approximately 42,400 cones per -- squirrel would be utilized. Since this far exceeds the number of cones

1' 1 ' 1 ..

i that were available to the squirrels in the fall of 1967, it is apparent

1 (

that they either utilize cones for a shorter duration, rely on other -foods, emigrate, die, or consume fewer cones per day.

It is unlikely that squirrels utilize cones for a shorter duration,

as C. Smith (1965) and M. Smith (1967) both found that conifer seeds

were the major food during this period. C. Smith (1965), in southern

British Columbia, found that conifer cones were available during the

entire year, and except for fungi, other foods did not become available '

until July.

It is also unlikely that foods other than spruce seed constitute a

major portion of the red squirrel's diet in interior Alaska (Dice 1921,

Murie 1927, Brink 1964, Smith, M. 1967). The homogeneity of the white

spruce stand on the Bonanza Creek study area appears to offer no alter-'-

native food source. ,_ It seems likely that fewer than 156 cones per day are consumed by

red squirrels. Pruitt and Lucier (1958), over a 3-year period of obser-1_.

'-' vations near Fairbanks, Alaska, found that red squirrels were seldom

active when the ambient air temperature was below -32°C (-25°F). They

stated (1958: 444): "In the subarctic taiga red squirrels become ._

._ subterranean and subni vean animals in winter ... ", and " ... the environ-

mental conditions experienced by red squirrels in winter are not those

of macroclimate but resemble more closely those experienced by Sorex ....

.... and Clethrionomys." Be cause of the subterranean and subni vean habits of

red squirrels and shortened period of daylight, I would expect that

---

-

-'-

'-

'-

-....

-

""'

34

during the winter a reduction in daily food consumption by red squirrels

might occur in interior Alaska.

POPULATION DENSITY 1-

- At no time during the study was more than one squirrel observed caching cones simultaneously on a midden, nor one squirrel caching cones

on more than one midden. From this observation and the literature (Gordon

1936, Clarke 1939, Kilham 1954, Smith, C. 1963, 1965, Smith, M. 1967) it

·~

~ ·~

1 was assumed that each active midden on the study area was occupied by one

,,

squirrel.

In the winter of 1964, after a cone crop fai1ure, M. Smith (1967)

estimated a population of one squirrel per 1.6 ha (4 acres) on the Bonanza

Creek study area, and during the winter of 1965, after the second sucees-

sive cone crop failure, the population had decreased to one squirrel per

4.8 ha (12 acres). Smith determined the population density by recording

the number of active middens on the study area. Since there were 23

active middens on the study area during the present study in the fall of

1967, a population of 23 squirrels was assumed. This represented one

·- squirrel per 0.9 ha (2.2 acres). '-

M. Smith (1967:34) noted, "A number of smaller, inactive middens were

interspersed among the larger active ones. These middens probably repre-

._ sent territories normally occupied only during years of good cone - production and when active might raise the density to one squirrel per 1.2 ha (3 acres)."

._ Two areas were discovered on the study area that possibly were old,

- inactive middens. If these had been occupied in the fall of 1967, a population of one squirrel per 0.8 ha (2 acres) would have been present .

... This estimate, or the actual population (one squirrel per 0.9 ha), does

... 35

...

36

not seem to be unreasonably high, because red squirre1s have been observed

·- in population densities much greater than that recorded on the study area in the fall of 1967. Klugh (1927) estimated 2 squirre1s per 0.84 ha (2

acres) in spruce woods in New Brunswick. Hatt (1929) observed a popu1a-

tion density of one squirrel per 0.73 ha (1.8 acres) on a 4 ha (10 acre)

stand of mature red spruce (Picea rubens), and Halvorson (1964) observed

a fall density as great as one squirrel per 0.27 ha (.66 acres) on an

island in Flathead Lake, Montana.

It appeares that the population density on the Bonanza Creek study

area fluctuates considerably, depending on the availability of white

spruce cones. Both M. Smith (1967) and Brink (1964) concluded that during

food shortages red squirrels emigrated from white spruce to black spruce

(Picea mariana) and th at black spruce acted as a buffer habitat.

M. Smith (1967) postulated that cone production on the Bonanza Creek

study area would be sufficient to support a squirrel density as great as

·- one squirrel per 1.2 ha (3 .acres) even in years of light to medium cone ._

production. While the cone crop on the study area was c1assed as medium

during 1967, production was from 56,700 to 177,100 cones per hectare

- (22,950 to 71,700 per acre). This represents a number far in excess of '-

the cones needed by the population of squirrels on the study area in 1967.

It is obvious that even a 75% smaller cone crop would yield 14,180 to 44,275

cones per hectare (5,750 to 17,900 per acre). This cone crop would prob-._

able be adequate to support a population of one squirrel per 0.8 ha (1.97

acres), the maximum number of squirrels the study area appears to have .....

supported based on the number of active and old inactive middens present . ....

It follows that beyond a certain level of cone production (approximately

·~· '-~~ :r;f

~-

΀ J, ~ .A

! ~ ., i j

~

l 1

·-

-

"-

'-

'-

._

._

.....

.....

...

....

37

14,000 cones per hectare), population density of red squirrels on the

Bonanza Creek study area is lirnited by factors other than food supply,

probably by vigorous territorial behavior.

r

-

-

·-

--

TERRITORI ALITY

Hinde (1956) defines the function of territorial behavior as any

advantage that this behavior gives, which would be reduced by a change in

this behavior. This definition implies natural selection, and C. Smith

(1963) discusses the selective advantage th at territoriali ty gi ves red

squirrels. He postulates that food storing and territoriality are the

resu1t of selective pressures for gathering the optimum amount of food

with a minimum of effort. The most efficient means of gathering cones

by red squirrels would be to gather all the cones in trees nearest the

midden, thus minimizing the distance the cones would have to be carried.

C. Smith (1963:58) states, "This would mean that cones would be harvested

in separate areas. The territorial system in Tamiasciurus does provide

individua1s with the optimum conditions for harvesting a food supply and

- at the same time allows the species as a whole to exploit the environment

--._

.....

....

...

....

....

in an efficient manner."

Territoriality in the red squirrel has been widely discussed in the

literature (Hatt 1929, Gordon 1936, Fitzwater 1941, Smith, C. 1963, 1965,

Smith, M. 1967, and others). Red squirrels in northern latitudes exhibit

stronger territorial behavior than red squirrels in southern latitudes .

This behavior has been ascribed to the more varied food supply in its

southern range and accordingly a lesser need for stored food during the

winter .

Vocalization

Vocalization plays an important part in the maintenance of a territory .

Alarm, aggressive, and territorial calls were identified on the basis of

38

i'

1'-rr ,_ 39

C. Smith's (1963) discussion of vocalization in red squirrels.

Alarm calls were a series of short, staccato notes, usually issued at

my approach, and usually gave way to the aggressi ve call as I neared the

squirrel. Aggressive calls were more continuous than alarm calls, but

with less amplitude and not as smooth as a territorial call.

The territorial call had a rattling sound and was issued periodically

during a red squirrel's daily activities. Territorial calls were markedly

absent during periods of falling snow and heavy rain. On the five

occasions that different squirrels were observed storing a mushroom on a

limb, each squirrel never ~ailed to issue a territorial call immediately

after depositing the mushroom.

While actively caching cones, squirrels frequently issued territorial

~ calls. On five occasions, while the observer timed the caching activity

- of red squirrels, it was noted that territorial calls occurred on an average of 14 minutes apart, but varied from 3 to 60 minutes.

._ Kilham (1954:253) compared the frequent issuance of territorial calls

._ by red squirrels to the territorial song of birds and stated, "Periodic

song advertised occupancy of the territory, warning other squirrels to

._ keep off." Gordon (1936: 171) also likened territorial calling of pine

- squirrels CI· ~· fremonti) to territorial calling in birds. He observed, " ... churring served the same purpose as soyg in the territorial behavior

- of birds for warning other individuals that the singer was ready to defend

... its area against invasion." C. Smith (1963:17) wrote that vocalization

in red squirrels and Douglas squirrels CI· ~· douglasii), " ... seemed

to have the sole function of advertising ownership of terri tory." ...

The usual territorial call was about 5 seconds duration. This

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corresponds to the observations by C. Smith (1963), who found the

territorial cal1s to be usually 1 to 4 seconds. Smith observed territorial

calls by Douglas squirrels that were as long as 6.5 seconds. No calls

of that length were observed during this study, but on severa! occasions

two territorial calls were issued in rapid succession, which even when

combined, were never longer than 10 seconds.

During the caching period, territorial calls were heard during all

daylight hours, but with greatest frequency after 0900 (Alaska Standard

Time). The frequency of calling was not suppressed by light rain or fog.

C. Smith (1963) noted that territorial calls were suppressed by heavy

rain, but that light rain had no effect. Falling snow seemed to suppress

territorial calls and activity in general on the Bonanza Creek study area.

Territorial calls were often answered by neighboring squirrels, but

no pattern of frequency of answering could be discerned during this study.

C. Smith (1963) observed that territorial calls were not usually answered

by neighboring squirrels.

The importance of vocalization in the maintenance of a territory was

obvious in an observation in which C. Smith (1963) prevented vocalization

of a territory owner, and a neighboring squirrel entered the territory

and pilfered stored cones .

Territorial Disputes

C. Smith (1963) observed 53 territorial disputes in 111 hours (0.57

disputes per hour) during which the exact position of the territorial

owner was known. Although Smith contends that 0.57 disputes per hour was

higher than the yearly average because of the time of his observations

and conditions on his study area, territorial disputes occurred much less

,-41 -

1

- frequent1y on the Bonanza Creek study area. 1 observed on1y eight ter- 1 ritoria1 disputes during two months of intensive observations. In the l) l'

eight disputes, the owner of the territory initiated the action on every

- occasion by immediately giving chase when the intruding squirrel was discovered.

One of the disputes began when 1 observed a squirre1 intruding on

- another squirrel' s terri tory. Immediately after sighting the intruding

squirrel, the territory owner came from its midden, without hesitation

issued an aggressive call, and began rapidly chasing the intruding

squirrel. The chase progressed rapidly around tree trunks and along the

- ground, until the intruder was chased about 30 rn to the west of my position and out of sight. For 10 minutes, repeated aggressive and ter-

- ritorial calls between the two squirrels were heard.

This dispute was typical of the other territorial disputes observed

during the study and those recorded in the literature. Gordon (1936) and

~ Kilham (1954) both described territorial disputes that were similar to ._,

those observed in this study. C. Smith (1963) observed that the typical

territorial chase lasted less than 2 minutes and ended when the pursued

squirrel left the territory of the pursuer. None of the territorial

- chases observed during the study lasted more than 2 minutes. A squirrel intruding on another squirrel's territory often attempted

to conceal himself from the territory owner. On another occasion while I

was watching a squirrel on its midden (squirrel A), an intruding squirrel

(squirrel B) entered the territory from the north. As squirrel B came

towards me, it became alarmed and gave an alarm call. This call appar-

ently alarmed squirrel A, as it immediately came from his midden toward

- squirrel B. Squirrel B may have seen squirrel A first, because it abruptly ,_ ascended a tree and lay rnotionless and flattened out on a lirnb 5 rn from

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the ground. Squirrel A went directly under squirrel B because it was by

then alarrned by my presence. Squirrel A continued on, picked up a cone,

and began hauling it to its rnidden. I then stood up and alarrned squirrel

A, and it scurried onto a tree near squirrel B and gave an alarrn call .

During this tirne squirrel B had not rnoved, but squirrel A finally saw

squirrel B and abruptly ended its alarrn call and dashed after squirrel B.

The chase lasted 1 minute and continued for 50 rn. After the chase ended,

squirrel A, the victorious owner, issued severa! territorial calls before

returning to its rnidden.

Seton (1909) and C. Smith (1963) cite observations of an intruding

squirrel acting in "a cowardly rnanner" that contrasted sharply wi th the

behavior of the owner. Gordon (1936:171) also observed an intruding

squirrel on a strange territory and stated, "· .. to the hurnan observer

it gave the impression of knowing that it was trespassing."

Territory Size

During the cone-caching period, the territories of squirrels 9SE and

12C were deterrnined from sightings of the squirrels and by rnapping the

most distant points from their rniddens at which they were observed. The

size of their territories was 0.57 ha and 0.36 ha, respectively .

To estirnate the average territory size on the study area. the calcu-

lated mean distance between rniddens (68.6 rn, see The Midden and Its

Location) was used as the diarneter of the "average" terri tory, an area

of 0.37 ha. This average size is comparable to the range of the average

territory size of red and Douglas squirrels (0.76 ha and 0.41 ha) on two

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of C .. Smith's (1965) study areas, and with Fitzwater's (1941) observations

in which he found the territory size of four red squirrels to be 1.13,

0.36, 0.12, and 0.65 ha, respectively.

Terri tory Change and Expansion

On the Bonanza Creek study area, M. Smith (1967) found that territory

ownership changed frequently in the winter of 1964-1965, following a sea-

son of cone crop failure. He attributed the territory changes to

depletion of the cone supply on the respective middens. In 1967 obser-

vations of marked squirrels indicated that after the caching period, sorne

breakdown or adjustment of territories occurred even though no scarcity

of cones existed.

In 68 trap-nights, from October 21 to November 3, 10 squirrels were

captured. Five squirrels were successfully marked with number one Monel

fingerling tags and Nyanzol "A" dye. Three of the fi ve were also marked

with a colored plastic, bell-wire loop attached to the ear tag.

The first trapped squirrel was marked on October 21 on midden 9SE and

was observed frequently thereafter. By this time, caching activity had

ended, and observations indicated that squirrel 9SE was ranging farther

from his midden than during the caching period. On November 1, squirrel

9SE was observed about 20 rn from midden lOS, chasing another squirrel in

what appeared to be a territorial dispute. As the observer moved closer

to the activity, the unmarked squirrel ran to the southeast and out of

sight. Squirrel 9SE then proceeded on to midden lOS (49 rn from midden

9SE) and entered the midden. After periodically emerging from and re-

entering the midden, he left midden lOS and returned to his midden (9SE) .

On November 3 squirrel 9SE was observed foraging again on midden lOS and

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traveling in a circular route back to his midden. This observation rep-

resented a definite expansion of territory, because during the caching

period the observer identified a squirrel actively caching cones and

defending midden lOS, while squirrel 9SE was only defending midden 9SE.

Midden lOS was a rather small midden, and the investigator suspected that

a young squirrel had occupancy of it until squirrel 9SE took·possession.

On October 25 a squirrel was marked on midden 7SE. After being marked,

this squirrel was frequent ly observed feeding and res ting near his midden.

However, on December 14, squirrel 7SE was observed feeding on midden 9W

(111 rn from midden 7SE). As the observer approached, the squirrel took

refuge in the midden. Midden 9W had been actively defended throughout

the cone-caching period by another squirrel, but later, tracks in the

snow indicated that midden 9W was only periodically active. Again, this

midden was small, and its former occupant could have been a young squirrel

unable to adequately defend the midden. Squirrel 7SE also retained owner-

ship of midden 7SE because he was later observed defending that midden.

C. Smith (1963) also observed sorne changes in territories which suggested

that young squirrels may have been the occupants that lost the territories.

Trapping and marking yielded another illustration of terri tory change.

On November 1 a squirrel which had been trapped and marked on midden 3N on

October 24 was found dead in a trap on midden C-1 (Fig. 1). On November

3, another squirrel was trapped and marked on midden C-1. This squirrel

was later observed on midden 7W (190 rn from midden C-1) where he was

successfully defending a territory. Later in the winter, both middens

3N and C-1 were occupied and defended by an unmarked squirrel.

Interspecific competition in red squirrels, as indicated by their

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territorial behavior, is energetic and exigent. On midden 3N a squirrel

was found dead in a trap, and at the same time a squirrel was observed on

the midden only 1.5 rn from the trap containing the dead squirrel. The

trap had been opened at 1345 the previous day, and the dead squirrel was

found at 1000 the fo1lowing day. With daylight from 0739 to 1531 on that

date, only 4.5 hours of daylight were available in the period between

trap checks. Not knowing when the dead squirrel was trapped, one can

assume that the territory was reoccupied within less than 4.5 hours from

the time when the dead squirrel was trapped.

C. Smith (1963) observed seven cases of a change in territory owner-

ship. Four of the changes resulted from the author's activities, and

Smith cited severa! possible reasons for the other territorial changes:

(i) young age of the owner and the inability to defend a territory; (ii)

fatigue from frequent territorial disputes with neighboring squirrels,

and the resultant inability to defend territories against vagrant squirrels

that were often attracted to the dispute; (iii) recent acquisition of a

territory and the subsequent lack of knowledge of the territory by the

new owner.

Linduska (1950) suggested the presence of transient or vagrant

squirrels with no fixed home ranges, and C. Smith (1963) found sorne

territorial tolerance by a mother for her young. Perhaps sorne of the

smaller middens on the Bonanza Creek study area represented relatively

recent establishment of ownership by vagrants or young squirrels. The

permanency of these middens may depend on the availability of food or

the young squirrel~ developing ability to defend a territory outside of

its mother's territory.

The greatest change in territorial ownership probably occurs in June

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and July after the young have been weaned. M. Smith (1967) found that

this observation occurred on the Bonanza Creek study area in 1965. How-

ever, it appears that the territorial structure in red squirrels is

subject to change at any time during the year, and that competition can

at times be extremely vigorous. During the caching period the territor-

ial structure is probably the most rigid, because a change in ownership

would probably result in the loss or gain of a year' s food supply .

Territorial Boundaries

Observations indicated that territorial boundaries were well recog-

nized by red squirrels. In one observation, two squirrels were sighted

chasing each other just before their dispute ended. After the chase the

two squirrels were in separate trees about 10 rn apart; and each period-

ically issued territorial and aggressi ve caUs. A third squirrel was

sighted as he approached on a fallen tree to within 6 rn of a line between

the other two squirrels. He also advertised his presence with a

territorial call. No aggressive action was noted among the three

squirrels, and after 4 to 5 minutes they all parted in defferent direc-

tions. Since it appeared that the three squirrels were aware of each

other's presence and that no aggressive action was elicited, it is assumed

that they were well aware of their respective territorial boundaries.

On September 18, off the study area, two squirrels were observed in

aggressive action that illustrated the exactness of territorial boundaries.

Squirrel A was hauling cones to his midden from an area adjacent to the

south side of a ski trail. Squirrel B approached squirrel A, but remained

on the north side of the trail. Both squirrels were frequently issuing

aggressive calls, and when squirrel A carried a cone south toward

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his midden, squirrel B would dash across the ski trail and give an aggres-

sive call. Squirrel A would immediately return to the area and squirrel

B would accordingly retreat to the north side of the trail. This action

continued for about 5 minutes until squirrel B departed to the north. It

appeared that squirrel B was attempting to take possession of the area

where the cones were located; however, squirrel A persisted in defending

it as part of his territory. The action appeared to illustrate the

importance of the ski trail as a territorial boundary, which in turn

indicates that landmarks might be important in delineating territorial

boundaries .

C. Smith (1963) observed that in two territorial chases, the pursuing

was reversed when the pursuer entered the territory of the pursued.

Kilham (1954) noted that during numerous disputes between two neighboring

squirrels, the chase would often be reversed when the pursuit reached a

dead map1e limb lying on the ground. Apparently, the limb represented a

territorial boundary beyond which the pursuer would have 1ess courage and

the pursued would gain courage and the chase would be reversed.

C. Smith (1963) noted the presence of occasional neutra! areas between

territories and suggested that boundaries adjacent to neutral areas were

not as well defined as those between adjacent territories.

NON-TERRITORIAL ASSOCIATIONS

On four occasions two squirrels were observed together in what

appeared to be harmonious association. The first such observation was on

September 13, during the height of the caching activity. 5quirrel 95E

was observed in a tree approximately 10 rn from the ground, with a cone in

his mouth. Another squirrel was in the same tree and was chasing squirrel

95E, but not with great speed as in a normal territorial dispute.

5quirrel 9SE came down the tree, deposited the cone at the base of the

tree, and immediately ascended the tree again. They chased each other,

as if playing, from branch to branch and around the trtmk for 1.5 minutes.

An attempted coitus was observed while the squirrels were in the tree.

After the coitus attempt, squirrel 95E descended the tree and rapidly ran

around and inside of a large rotten stump several times before returning

to its midden. The other squirrel remained in the tree and was not seen

again. Throughout the observation, territorial calls were given period-

ically by both squirrels.

No similar activity was observed during the remainder of the caching

period, but on December 14 two squirre1s disp1ayed similar behavior near

midden 35. One squirre1 was from midden 3~ and the other had been marked

on midden C-1. The behavior observed was simi1ar to that described in

the above observation, except that the squirre1s were not chasing each

other as steadi1y. Chasing wou1d occur for about 30 seconds, then the

squirre1s would fo1low each other from branch tip to branch tip as if

searching for cones or buds. Coitus was attempted by squirre1 35.

5quirre1 C-1, the recipient of the attempted coitus, was a male. The

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squirre~s remained in the same tree for 20 minutes after which 3S descended

the tree and returned toits midden. Squirrel C-1 remained in the tree,

and the observer did not see it again. At a later date, squirrel C-1 was

observed defending a territory around midden 7W.

On December 20, two squirrels were again observed in one tree on the

study area (Paul Krasnowski, persona! communication), but the exact loca-

tion was not noted.

Hatt (1929) observed that sporadic attempts at coitus outside the

normal breeding season were common, and Layne (1954) observed a chase

between two individuals on December 30 in which a male attempted to mount

a female. Both squirrels were collected and neither were in breeding

condition. C. Smith (1963) found that juvenile males would frequently

engage in sexual play.

C. Smith (1965:16) observed evidence of a temporary breakdown in

territorial behavior as he observed two adult squirrels eating pollen

from staminate cones in the same Douglas fir tree. He observed this

behavior in five pairs of red squirrels and two pairs of Douglas squirrels,

each at a different location. Smith noted that territorial and aggressive

calls were given, during these encounters, by one or both of the squirrels .

He observed sorne chasing but stated, " ... on the whole the re was a. far

greater degree of tolerance than had been observed at any other time

except during mating act i vi ty."

The squirrels that Smith observed were all engaging in similar

activity; consuming staminate Douglas fir cones. Smith points out that

this food source is available for a few weeks in the spring, and that

" male cones are not stored by the squirrels so there is no way or need

- 50 to effectively defend this food source. The circumstances of this

- breakdown of territorial defense are then consistent with the function of territorial behavior, which is the defense of a food supply that is

stored during the winter ... "

- In view of the importance of territoriality to the maintenance of food supplies, non-territorial associations are more common in the

southern part of the red squirrel's range. Layne (1954) found that during

- the colder months, squirrels lived in community den trees that housed

three or four squirrels, and Petrides (1941) observed colonies of red

squirrels living together in underground burrows.

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APPENDIX I

Calculation of the total cone crop of white spruce, and the per cent of harvest by red squirrels on the Bonanza Creek study area.

Calculation of cone crop

Mean number of cones per plot:

Lower range (from table 3)

X = 14,088 ! 6,964 (P=.OS) S. D. = 6,635

Higher range (from table 3)

X= 15,446! 6,798 (P=.05) S.D. = 6,475

S.E. = 2,709 S.E. = 2,644 cv = 0.449 cv = 0.419

Range = 7,124 to 22,244 cones per plot.

Area of plot = 0.1256 ha. Area of study area = 20.88 ha.

Tot al cone crop :

7,124 to 22,244 x

0.1256 20.88

X= 1,184,308 to 3,697,888 (P=.05) cones.

Calculation of cone harvest

Mean number of cones per midden:

Large middens (14 present on study area)

X= 13,410 ± 1,708 (P=.20) SD = 785 SE = 555 cv = 0.058 Range= 11,702 to 15,118

Small middens (9 present on study area)

3,000 to 5,000 cones per mid