Density and seasonal food habits of bobcatson the Three Bar Wildlife Area, Arizona

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Authors Jones, James H., 1952-

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DENSITY AND SEASONAL FOOD HABITS OF BOBCATS

ON THE THREE BAR WILDLIFE AREA, ARIZONA

by

James Henry Jones

A Thesis Submitted to the Faculty of the

SCHOOL OF RENEWABLE NATURAL RESOURCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN WILDLIFE ECOLOGY

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 7

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of re­quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg­ment the proposed use of the material is in the interests of scholar­ship. In all other instances, however, permission must be obtained from the author.

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

MAN S. SMITHNORMANProfessor of Wildlife Ecology

~7 /97SDate

ACKNOWLEDGMENTS

I thank Dr. Norman S. Smith for his guidance and advice through­

out the study and Drs. Lyle K. Sowls, C. Roger Hungerford and Russell

P. Davis for their instruction during my tenure. Deep thanks are given

to Albert and Karen Le Count and the AG&F Research Division and Three

Bar crew for their help and support, also to Norm Woolsey, Bill

Workman, Dr. Ross C. Babcock, Jr., Chuck Hanson and the folks at the

Arizona-Sonora Desert Museum, and JD. Finally, but not leastly, I

thank LH and ML for all they did, have done, and are still doing.

In memoriam (?), a reflection on the words of H. L. Mencken:

"For every complex problem there is a simple solution — and it is

wrong."

iii

TABLE OF CONTENTS

LIST OF ILLUSTRATIONS.......................................... v

LIST OF TABLES ................................................ vi

A B S T R A C T ........................................................ vii

INTRODUCTION.............................................. .. . 1

STUDY A R E A .............................................. 4

METHODS AND MATERIALS ............................................ 7

Density, Home Range and Sex/Age StructureD i e t ...................................Prey Availability . . . .................Population Trend Techniques ....................... . . . . 10

RESULTS.......................................................... 11

Density, Home Range and Sex/Age Structure ................. 11D i e t ........................................ 11Prey Availability.......................................... 14Population Trend Techniques ............................... 14

DISCUSSION...................................................... 20

Density, Home Range and Sex/Age Structure .................. 20Diet and Prey Availability............................... 24Population Trend Techniques . . . . . . . . . . . . . . . . 35

APPENDIX A: STANDARD MEASUREMENTS OF BOBCATS ................... 37

APPENDIX B: STANDARD MEASUREMENTS OF RODENTS ................. 39

APPENDIX C: MONTHLY PRECIPITATION ............................. 4l

LIST OF REFERENCES.............................................. 43

Page

iv

O-CO ON

LIST OF ILLUSTRATIONS

1. Bobcat study area on the Three Bar Wildlife Area,Arizona..................................... 5

2. Trapping locations of marked carnivores and trails ofbobcats when pursued by hounds on the Three Bar Wildlife Area, Arizona . . . . . . . . . . . . . . . 13

3» Bimonthly frequencies of occurrence of principle prey items in bobcat scats collected on the Three Bar Wild­life Area, A r i z o n a ............................ l6

4. Monthly rodent availability and consumption by bobcats onthe Three Bar Wildlife Area, Arizona. .................... 33

5. Monthly lagomorph availability and consumption by bobcatson the Three Bar Wildlife Area, Arizona . . . . . . . . . 34

Figure Page

v

LIST OF TABLES

1. Location, sex, age and marking data for carnivores trapped and marked on the Three Bar Wildlife Area,Arizona.................................. 12

2. Percentages of occurrence of prey items in 176 bobcatscats collected on the Three Bar Wildlife Area, Arizona . 15

3* Numbers and frequencies of rodents trapped monthly on theThree Bar Wildlife Area, Arizona ....................... 17

4. Numbers and frequencies of lagomorphs strip-censusedmonthly on the Three Bar Wildlife Area, Arizona ........ l8

5. Numbers of scats collected on monthly transects on theThree Bar Wildlife Area, A r i z o n a ............ .. . . . . 19

6. Percentages of occurrence of principle bobcat prey items— Western states . . . . . . ......................... • 28

7. Percentages of occurrence of principle bobcat prey items— Southern states . . . . . . . . . . . . . . . . . . . 29

8. Percentages of occurrence of principle bobcat prey items— Northeastern states . . . . . . ...................... 30

Table Page

vi

ABSTRACT

I trapped, ear-tagged, trailed with hounds, and collected scatsp

from bobcats (Lynx rufus) on 28.8 km of the Three Bar Wildlife Area in

central Arizona from May 1975 to May 1976. Their estimated density in

the transition between the upper and lower Sonoran life-zones of the

study area is approximately 0.28 per km . I grouped 176 bobcat scats into bimonthly samples and analyzed their contents to determine fre­

quencies of occurrence of prey items. Significant food items were

woodrats (Neotoma spp.), 31*8 percent; heteromyids, 15*9 percent; and

valley pocket gophers (Thomomys. bottae), 5*1 percent; lagomorphs, 37*5

percent; and egg shells, 10.2 percent. The frequencies of occurrence

of neither rodents nor lagomorphs varied significantly among the

samples. A non-significant number of bobcat scats contained deer

(Odocoileus spp., 2.8 percent) or javelina (Dicotyles tajacu, 0.6 per­cent) remains. I trapped rodents and strip-censused lagomorphs monthly

to determine prey availability. Both populations varied significantly

during the year but neither was significantly correlated with contem­

poraneous bobcat prey selection, indicating that bobcats are not

strictly opportunistic predators in this environment when prey species

are generally abundant. A "scent post" technique of censusing bobcats

was not successful. Numbers of scats collected varied significantly

between six monthly transects.

vii

INTRODUCTION

The bobcat is a predator of great potential interest to man —

economically by preying on domestic livestock and game species, and

ecologically by limiting prey populations and competing with other car­

nivorous animals. Although the bobcat has been studied in the north­

eastern United States (Hamilton and Hunter 1939; Hamilton 1940; Marston

1942; Foote 1945; Pollack 1949, 1950; Latham 1950; Westfall 1956;

Siegler 1971; McCord 1974), southeast (Progulske 1952, 1955; Davis

1955; Fooks 1961; Kight 1962; Marshall and Jenkins 1966; Conley 1968;

Conley and Jenkins 1969; Fritts 1973)» midwest (Dearborn 1932; Rollings

1945; Erickson 1955; Korschgen 1957), Rocky Mountains (Robinson and

Grand 1958; Gashwiler, Robinette and Morris i960, 1961; Crowe 1972, 1975a, 1975b; Bailey 1972) and California (Hunt 1920; Dixon 1925;

McLean 1934; Leach and Frazier 1953), few data have been gathered on

the bobcat in the Southwest. I undertook this study of bobcats on the

Three Bar Wildlife Area in central Arizona from May 1975 to May 1976

to find:

1. Bobcat density in the lower/upper Sonoran life-zone transition.

2. Seasonal diets of the bobcat in this habitat.

3* The relation of the bobcat's diet to prey availabilityw

4. A census technique for monitoring bobcat population trends on

the Three Bar Wildlife Area.

5- Preliminary data for estimating the bobcat's home range in this

habitat.

1

2

6. The sex and age structure of the bobcat population on the Three

Bar Wildlife Area.

The Three Bar Wildlife Area consists of 171 km^ of the Tonto

National Forest on the west side of Roosevelt Lake in central Arizona.

The U.S. Forest Service and Arizona Game and Fish Commission have had

a cooperative agreement since 19^9 to use the area for wildlife re­search and it has been ungrazed since 19^7. The area has been closed

to the hunting and trapping of predators since 1972, and mule deer (Odocoileus hemionus) and javelina hunting have been closely regulated

and monitored on the area during the past 12 years.The Three Bar extends from 600 m to 2500 m in elevation and

includes lower Sonoran desertscrub, upper Sonoran desert grassland and

chaparral, oak woodland and ponderosa pine associations, as defined by

Lowe (1964). Approximately ll6-km^ of the Three Bar are suitable des­ert mule deer habitat (the desertscrub, desert grassland and lower

chaparral). The Arizona Game and Fish Department has been studying

mule deer here since 1952 (McCulloch 1954) and has monitored the herds

carefully during that period. The 1959 deer survey and pellet count

on the Three Bar indicated a density of approximately 11.6 deer per 2km , but eight years of any deer hunting coupled with low fawn sur­

vival lowered the density to approximately 2.3 deer per km^ in 1964

(McMichael 1970) where it remained until 1971. The current density is

approximately 4.6 deer per km^ (Albert Le Count, personal communication 1976).

The decrease in deer density on the Three Bar corresponded with

a statewide decline in mule deer populations (Jantzen 1964) and this

has prompted a series of studies to determine the cause(s) of low fawn

survival in Arizona's mule deer herds. To assess the importance of

predation on fawns in limiting herd recruitment, the Department in 1970

enclosed 246 ha of typical mule deer habitat on the Three Bar to form

the Walnut Canyon Game Enclosure. The area was enclosed with chain-

link fencing approximately 3 m high, and a wire apron was placed around the base of the fence to form a barrier to predators. Bobcats and

coyotes (Canis latrans) were removed from the enclosure. No black

bears (Euarctos americanus) or mountain lions (Felis concolor) were

entrapped when the fence was completed. From 1971 to 1975 annual deer

herd composition and population counts on the Three Bar have been com­

pared with the same data from inside the enclosure. The results indi­

cate virtually complete fawn (and javelina piglet) survival inside the

enclosure, while survival outside has been significantly lower (xf =

56.87, df 4, P <.05 /he Count, personal communication 197(7). The

evidence suggests that bobcat and/or coyote predation on fawns (and

piglets) may be limiting herd size on the Three Bar.

Because bobcat predation on mature deer has been well docu­

mented (Young 1928; Harwell 1932; Dixon 1934; Dill 1947; Matson 1948;

Westfall 1956; Petraborg and Gunvalson 1962), it is quite feasible that bobcats could prey extensively on the more vulnerable fawns. This

possibility was the motivating basis for my study.

3

STUDY AREA

My study area extends from the Three Bar road (Forest Service

road 445) and the Baldy jeep trail on the north to the Mills Ridge road

on the south, and Arizona highway 188 on the east, to the top of the

first ridge west of the Walnut Canyon Game Enclosure on the west (Fig.p

1). This area is 28.8l-km (excluding the 246 ha in the enclosure)

and ranges in elevation from 655 m on the east edge to 1233 m on top of Rocky Point Ridge.

The vegetation includes lower Sonoran desertscrub, upper

Sonoran desert grassland and the lower edge of the upper Sonoran chap­

arral associations. The desertscrub is characterized by saguaro

(Carnegia gigantea), paloverde (Cercidium microphyllum), crucifixion

thorn (Canotia holocantha), jojoba (Simmondsia chinensis), catclaw

(Acacia greggi) and red brome (Bromus rubens)• The desert grassland

is primarily composed of fairy duster (Calliandra eriophylla), prickly

pear (Opuntia engelmanni), velvet mesquite (Prosopis juliflora),

eriogonum (Eriogonum wrighti), snakeweed (Gutierrezia sarothrae), wild

oats (Avena fatua), three-awn (Aristida spp.) and red brome. The

chaparral is mainly covered with turbinella oak (Quercus turbinella),

snakeweed and red brome. More complete descriptions of the vegetation

on the Three Bar are given by McCulloch (1954) and Dickerman (1955)•

McCulloch (1954) reported that the annual precipitation on the

Three Bar is 44.0 cm but for the past 20 years it has averaged only4

three e*,,

ROCKY P I. v

ROOSEVELT

LAKE

WALNUT CANYON

ENCLOSURE

DIRT ROAD

JEEP TRAIL

RIDGE TOP DRAINAGE

FENCE

KILOMETERS

Figure 1. Bobcat study area on the Three Bar Wildlife Area, Arizona

636.4 cm (Le Count, personal communication 1976). During the year of

my study the area received 44.7 cm of precipitation (Le Count, personal communication 1976).

METHODS AND MATERIALS

Density, Home Range and Sex/Age Structure

I set coil spring traps baited for bobcats from October 1975

through March 1976. I used Victor number 2 traps with 1 m chain and

toggle drags and Victor number 3 traps with 1 m chains welded to 80 cm stakes. I boiled all traps in water and creosote (Larrea divaricata)

oil to reduce odor and weatherproof the metal. I padded the jaws with

foam rubber and vinyl tape to minimize damage to trapped animals' feet.

I made mostly double pen sets similar to those described by Young

(1958), baited with parts of jackrabbit (Lepus spp.) or desert cotton­

tail rabbit (Sylvilagus auduboni) carcasses and a lure made with bob­

cat urine and anal glands, beaver (Castor canadensis) castor, decom­

posed fish oil, oil of catnip, skunk (Mephitis spp.) musk and glycerine.

I trapped mainly along ridge top saddles and wash bottoms and anywhere

I found fresh bobcat signs. I trapped for 21 trap-nights in October,

115 in November, 42 in December, 328 in January, 353 in February and

246 in March, during which time I made sets on all major ridges and

washes in the study area.

I immobilized trapped bobcats by holding their heads in a 1.5 m snare and injecting drugs into their thighs with l8-gauge needles on a pole syringe. I first injected 1 ml Atropine (1/120 g per ml)

to reduce salivation, followed in ten minutes by a dose of ketamine

hydrochloride (100 mg per ml) and acepromazine (0.1 mg per ml ketamine).7

I estimated dosages at 15 mg ketamine per kg body weight. I used

phencyclidine hydrochloride (100 mg per ml) to immobilize two badgers

(Taxidea taxus) and a raccoon (Procyon lotor). I applied neomycin-

sulfate gel to all immobilized animals' eyes to prevent dissiccation,

administered a 1 ml injection of Combiotic to each animal and squeezed

a penicillin-neomycin-sulfa ointment on all superficial injuries.

I placed a numbered aluminum tag in one ear of all bobcats,

the coyote and the grey fox (Urocyon cinereoargenteus), beneath which

I affixed a 7 cm x 5 cm oval of reinforced plastic colored blue, white,

orange or yellow, to allow visual identification at a distance. I took

standard body measurements and weighed each animal. I force-fed each

bobcat a gelatin capsule containing 100 glass beads for possible re­

covery in feces later (Sowls and Minnamon 1965). I attempted to ex­

tract an incisor from each bobcat for ageing by Crowe's (1972) tech­

nique and I qualitatively estimated each animal's age class (young,

adult, old, very old) by tooth wear. I tried to cause immobilized

animals to defecate by injecting 50 ml of yellow aniline dye into their

anuses but abandoned this technique because it failed.

On April 4, 7 and 8 Karen Le Count and I followed six hounds

as they hunted across the northwestern portion of the study area. We

attempted to resight marked animals or sight bobcats that had not been trapped.

Diet

I collected bobcat scats (feces) monthly along ridge tops where

the soil is coarse and scats are not covered, and in washes. Scats are

9very similar to those described by Murie (195*0 for southwestern bob­cats and I identified them on the basis of size, conformation, gross

composition, location and odor in comparison to a sample taken from

bobcats at the Arizona-Sonora Desert Museum.

I grouped the scats into bimonthly samples to indicate seasonal

diets and broke them apart individually to analyze their contents. I

identified the remains in these scats using four references as needed.

1. The key by Cockrum (i960) for osteological remains.2. The key by Moore et al. (197*0 for hair scale impressions made

by Williamson's (1951) technique, modified to use acrylic instead of

Gelva.

3. Personal collections of hairs and photomicrographs of hair

scale impressions.

4. Specimens from the University of Arizona mammal collection for

comparison.

Prey Availability

I set two 10 m x 10 m five-station grids, using a museum spe­

cial and Victor rat trap at each station, each month in each of the

three associations on the study area — desertscrub, desert grassland

and chaparral. I trapped each grid for five nights for a total of 100

trap-nights per association per month. Other than these grids I did

not attempt to census sciurids or geomyids, nor to index the abundance

of birds or bird eggs.

I censused lagomorphs by driving 25 km per hour for 10 km

along the Three Bar road five days each month and counting the

10

lagomorphs seen between the drainage ditches along the sides of the

road. I did this during the half hour before sunrise to correspond

with Smith's (1959) period of peak lagomorph activity in the area. I

did not census any mammalian prey larger than lagomorphs.

Population Trend Techniques

I first attempted to census bobcats using a modification of

Linhart and Knowlton's (1976) coyote census technique. I constructed

a census route of 40 stations at 0.5 km intervals along the Three Bar,

north and south loop, and Mills Ridge roads. I randomly allocated 20

scent and 20 visual (curiosity) attractants to the stations. I made

the scent attractants by grinding 0.5 g of dried catnip leaves in a

mortar and pestle and placed them in histological staining capsules on

the ends of 15 cm wooden sticks. I made the visual attractants by

hanging shiny aluminum muffin tins, 9 cm in diameter, from stiff wires

imbedded in the ground and standing 1 m high. I placed both baits in

the centers of circles of sifted soil, 1 m in diameter, along the sides

of the roads. I operated the census route during the full moon in June

for five nights and in August for four nights, recording all legible

tracks in the circles.

I tried an alternative census method by walking transects along

the tops of Rocky Point Ridge (2 km), Peters Mountain (1.5 km) and

.45-75 Ridge (3 km) during the first week of each month and recorded

the numbers of bobcat scats found. I conducted these counts from

October through March.

RESULTS

Density, Home Range and Sex/Age Structure

I trapped six different bobcats and retrapped one on the study

area. Three of these were male and three female, I believe that the

two toes found in a trap on March 3 belong to a seventh bobcat because

of the location of the trap in relation to other locations on the study

area where I trapped bobcats. I also trapped one coyote, grey fox,

raccoon and spotted skunk (Spilogale putorious), and two badgers during

the study. Data on all these animals are in Table 1 and Appendix A,

and trapping locations of carnivores marked are shown in Figure 2.

On April 8, while we were riding after a pack of hounds in Rock

Creek, Karen Le Count sighted an unmarked bobcat that the dogs had

flushed from a boulder pile. The hounds had followed a bobcat trail

on April 4 also, but she saw the only bobcat we observed. Both bobcat

trails are indicated in Figure 2.

I did not find any glass beads which I had fed to trapped bob­

cats in scats I collected and analyzed, nor was I able to extract in­

cisors intact from drugged bobcats for sectioning, I estimated the

trapped bobcats' ages from tooth wear only.

Diet

I collected 42 bobcat scats during the June-July period, 4l

during August-September, 23 during October-November, 19 during December-

January, 34 during February-March and 17 during April-May. In

11

Table 1. Location, sex, age and marking data for carnivores trapped and marked on the Three Bar Wildlife Area, Arizona.

Date Species Location Tag NoTag

. Color Ear Sex Age

10/29 Lynx rufus W end Peters Mountain 252 Orange L M Adult1/18 Canis latrans N side Rocky Pt. Ridge 251 Orange R F 1-2 yr.1/30 L. rufus Rock Creek 253 Blue L F Adult2/3 L. rufus Rock Creek 257 White L M V. old2/3 L. rufus Rock Creek 258 Yellow L M Old2/8 L. rufus E and Peters Mountain 259 Blue R F Old2/9 L. rufus E end Peters Mountain (Retrap of #253)2/10 Urocyon

cinereoargenteus SB end Peters Mountain 240 Orange L F mm mm

3/3 L. rufus* Mid-Loop Roads (Only 2 toes in trap)3/18 L. rufus Mills Wash 255 Orange R F Young

•This bobcat is tabulated because it is now an identifiable animal.

Hru

THREE_64/?

x 251

ROCKY PT V

ROOSEVELT253a

LAKE

ARIZONACANYON

ENCLOSURE

2N N CANID TRAP-SITE

o 2N N BOBCAT TRAP-SITE

= = = = = = DIRT ROAD

-------------- JEEP TRAIL

- w " * - RIDGE TOP— -----------DRAINAGE

FENCE

\ r id g e R6.4 /4 BOBCAT TRAIL

4 /8 BOBCAT TRAIL ^ |____

KILOMETERS

Figure 2. Trapping locations of marked carnivores and trails of bobcats when pursued by hounds on the Three Bar Wildlife Area, Arizona.

HVI

14

analyzing the scats I grouped kangaroo rats (Dipodomys spp.) and pocket

mice (Perognathus spp.) as heteromyids because I could not clearly dif­

ferentiate the remains of the two genera. For the same reason I com­

bined black-tailed jackrabbits (Lepus californicus) and desert cotton­

tails together as lagomorphs. The results of my analysis of the

contents of the 1?6 scats are listed in Table 2 and depicted graphi­

cally in Figure 3«

Prey Availability

The results of the rodent census are in Table 3» I recorded

standard measurements and weights of 303 of the 457 rodents I trapped. Mean weights and measurements of these animals are listed with their

standard deviations in Appendix B. The results of the lagomorph census

are in Table 4.

Population Trend Techniques

The beds of sifted soil at the census stations in June were not

deep enough for good tracking but I estimated that the scent posts were

visited by six foxes, two coyotes and one bobcat during 100 station-

nights. The visual attractants appeared to have been visited by four

bobcats during 60 station nights. I sifted more soil for the August

census to improve the legibility of the tracks, and found only one

possible bobcat visit during 160 station-nights.

I collected 42 bobcat scats along the transects on Peters Moun­

tain, Rocky Point Ridge and .45-70 Ridge from October through May.

Information regarding the spatial and temporal distribution of these

scats is in Table 5«

Table 2. Percentages of occurrence of prey items in 1?6 bobcat scats collected on the Three BarWildlife Area, Arizona.

Bimonthly Collection (number of scats)

Food Item

Jun.-Jul.(42)

No. %

Aug.-Sept. (41)

No. #

Oct.-Nov. (23)

No. %

Dec.-Jan. (19)

No. %

Feb.-Mar. (34)

No. %

Apr.-May (17)

No. %

Annual (176)

No. %

Any rodent 29 69.0 32 78.0 16 70.0 11 57.9 19 55.9 10 58.8 117 66.5Neotoma spp. 17 40.5 15 36.6 6 26.1 4 21.1 9 26.5 5 29.4 56 31.8Heteromyid 10 23.8 7 17.1 2 8.7 3 15.8 4 11.8 2 11.8 28 15.9Thomomys bottae 2 4.8 2 4.9 3 13.0 1 5.3 0 0.0 1 5.9 9 5.1Spermophilusvariegatus 2 4.8 0 0.0 3 13.0 1 5.3 1 2.9 1 5.9 8 4.5

Peromyscus spp. 3 7.1 1 2.4 0 0.0 0 0.0 0 0.0 1 5.9 5 2.8Ammospermophilusharrisi 0 0.0 0 0.0 1 4.3 0 0.0 1 2.9 0 0.0 2 1.1

Unknown rodent 5 11.9 10 24.4 3 13.0 3 5.3 6 17.6 2 11.8 29 16.5Lagomorph 13 31.0 16 39.0 8 34.8 8 42.1 14 41.2 7 41.2 66 37.5Odocoileus spp. 4 9.5 0 0.0 1 4.3 0 0.0 0 0.0 0 0.0 5 2.8Dicotyles ta.jacu 0 0.0 1 2.4 0 0.0 0 0.0 0 0.0 0 0.0 1 0.6Mephitis spp. 1 2.4 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 0.6Canis spp. 0 0.0 0 0.0 1 4.3 0 0.0 0 0.0 0 0.0 1 0.6Egg shell 8 19.0 4 9.8 0 0.0 0 0.0 0 0.0 6 35.3 18 10.2Unknown bird 0 0.0 1 2.4 0 0.0 0 0.0 4 11.8 2 11.8 7 4.0Unknown snake 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 2.9 1 0.6

5I

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J U N E -J U L Y

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AUGUST-SEPTEMBER

80

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FEBRUARY-MARCH

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RODENT

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HETEROMYIO THOMOMYS LAGOMORPH E66 SHELL MEOTOMA HETEROMYIO THOMOtm LAGOMORPH EGG SMELL

OCTOBER-NOVEMBER APRIL-M A YFifitire 3» Bimonthly frequencies of occurrence of principle prey items in bobcat scats

collected on the Three Bar Wildlife Area, Arizona

&

Table J>. Numbers and frequencies of rodents trapped monthly on the Three Bar Wildlife Area, Arizona. — Three hundred trap-nights/month.

MonthSpecies Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Annual

Dipodomys merriami 3 7 6 15 18 24 24 24 21 17 8 167Peromyscus boylei 1 0 10 15 12 10 7 13 7 6 1 82Neotoma albigula 6 6 12 7 4 2 5 15 11 5 5 78Perognathus baileyi 4 6 11 6 3 6 8 3 8 7 5 67Onychomys leucogaster 0 0 3 1 4 7 6 8 2 2 4 37Ammospermophilusharrisi 2 0 1 0 1 1 3 8 3 4 1 24

Spermophilus variegatus 0 1 0 0 0 0 0 0 0 0 0 1Thomomys bottae 0 0 0 0 0 0 0 0 0 0 1 1

Total 16 20 43 44 42 50 53 71 52 4l 25 457Frequency(rodents/trap-night) .053 3̂ .143 .147 .i4o .167 .178 .237 .173 .137 O .138

Ho

Table 4. Numbers and frequencies of lagomorphs strip-censused monthly on the Three Bar WildlifeArea, Arizona. — Fifty km/month.

MonthSpecies Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Ann

Lepus californicus 0 1 2 5 4 5 3 5 3 6 5 6 43Sylvilagus auduboni _29 J £ -50 _29 .25 11 17 20 24 28 43 6l 382

Total 29 46 52 34 29 16 20 25 27 34 46 67 425

Frequency (lagomorphs/km) .83* .92 1.04 .68 .58 .32 .40 .50 .54 .68 .92 1.34 .73

♦Only 35 km censused in June.

H00

19Table 5« Numbers of scats collected on monthly transects on the

Three Bar Wildlife Area, Arizona

MonthTransect Oct Nov Dec Jan Feb Mar Total

Peters Mountain 6 3 2 0 5 2 10

.45-70 Ridge 3 1 1 0 4 3 12

Rocky Point Ridge _2 JL _0 _0 _6 12

Total 11 5 3 0 12 11 42. z x

DISCUSSION

Density, Home Range and Sex/Age Structure

Based on the six bobcats I trapped and marked, the probable

seventh bobcat that chewed off two toes to escape, and the unmarked

bobcat that Karen Le Count saw, I estimate the density of bobcats on

the area during the study to have been approximately eight bobcats per 2 228.81 km , or 0.28 cats per km . Any density estimate is a function

of space and time, and is dependent on such factors as constant natal­

ity, mortality, emigration, immigration, and even distributional flux

in the population while it is being sampled. However, within the con­

straints of sampling a mobile population on a fixed area over a pro­

tracted period of time, I believe that my figure is a reaxonable

approximation of at least the minimum bobcat density on the Three Bar.

Bailey (1972) found in Idaho a resident bobcat density of 0.052per km . Grinnell, Dixon and Linsdale (1937) crudely estimated a den-

psity in California of O.38 bobcats per km and the U.S. Forest Service

(1942) reported bobcat densities of 0.10 per km^ in Michigan, 0.09 per 2 2km in Wisconsin and 0.07 per km in Minnesota. The minimum density

of bobcats that I found on the Three Bar is near the maximum found in

the literature.

The only indices of bobcat home range size that I gathered were

the recapture of one female (#253) 2.3 km from her initial point of

capture ten days earlier and the path of the unmarked bobcat that Karen

20

21

Le Count and I chased with hounds in Rock Creek. In addition, Karen

reported that on February 27 she trailed a bobcat with hounds up

Sycamore Creek (approximately 5 km north of the Three Bar) for a linear

distance of almost 8 km. Lowe (1958) and Toll, Baskett and Conoway

(I960) noted that the areas in which swamp rabbits (Sylvilagus

aquations) and marsh rabbits (S. palustris) ran when chased by dogs

corresponded to the home ranges of those animals as determined by trap­

ping. The advantage to a harried animal in staying within familiar

territory is obvious. Assuming that bobcats exhibit the same behavior,

the minimum area, and thus minimum home range, which the unmarketed bob-2cat on April 8 circumvented was approximately 1.3 km . We trailed the

bobcat on April 4 in and around the same area and if these two obser­

vations were of the same animal, as seems likely, then its minimum home

range (as circumscribed by the two chases) is slightly over 2 -km2.

A minimum home range of 1.3 to 2+ km2 is within Seton's (1929)

estimate of a maximum bobcat home range (in an area with ample food)

of 4 km . Other home range estimates have been made by Kight (1962)2

as 0.6 to 2.6 km in South Carolina, by Marshall and Jenkins (1966) as 2

2.5 to 4.6 km also in South Carolina, and by Pollack (1949, 1950) as 2

3.9 to 14.2 km in the northeast. All are fairly close to my minimumparea estimate of 1.3 to 2+ km . However, the relatively high density

of bobcats on the Three Bar might account in part for the disparity be- 2tween my +2 km home range estimate and Rollings' (1945) Minnesota

2estimate of 25 to 38 km , Erickson's (1955) Michigan figure of 39 to 5? km2 and Marston's (1942) Maine range of 4? to 104 km2.

22

The distances traveled by the female previously mentioned

and the bobcat that Karen Le Count trailed up Sycamore Creek

(2.3 km and 8 km respectively) are within the range of bobcat movements

given in the literature. Marshall and Jenkins (1966) reported daily

movements of 0.5 to 5*7 kmt Rollings (1945) estimated 1.2 to 6.0 km per

night, Robinson and Grand (1958) recovered 50 percent of their marked

bobcats within 1.6 km of the point of capture (the maximum recovery

distance during the first month was 10.2 km), Pollack (194-9, 1950)

found nocturnal movements of 3*2 to 8.0 km per night, and Erickson

(1955) estimated that bobcats' mean daily travel radius as 2.3 km. My

data from the Three Bar fall within the extremes.

Bailey (1972) found that bobcats in Idaho maintained relatively

exclusive territories, particularly with respect to conspecifics of the

same sex. Seidensticker et al. (1973) indicated that mountain lions

exhibited the same type of mutual avoidance as described by Hornocker

(1969) that Bailey's bobcats showed, but the lions appeared to be more

tolerant of one another and maintained less rigid territories than the

bobcats. The Three Bar bobcats seem to have flexible territories more

like those of Seidensticker's lions than Bailey's bobcats. Evidence

for this hypothesis is the capture of two old males (#257 and #258) on the same night within 100 m of each other. Furthermore, I caught two

females (#253 and #259) within 200 ra of each other on consecutive nights.

Two possible explanations for the synchronous presence of the

two males at Rock Creek would be the pressure to utilize a limited

23environmental resource (i.e., open water), or perhaps the presence of a

female in estrous that lured them together. Early February, when the

event occurred, should have been near the peak of the mating season

(Duke 1954; Young 1958), thus the latter explanation may be more plaus­

ible.

The proximity of the two females (after catching one of them,

#253» on Rock Creek four days before catching the two males there) may

have been coincidental or might be due to the fact that #253 was a

younger animal in a transient status (Seidensticker et al. 1973)• In

effect, she may have been roving through the area without a defensible

territory of her own, and since she was not a resident was tolerated

by #259.

The sex ratio I found of 1:1 is from too small a sample to be

meaningful. Sex ratios determined by others range from 0.4 males per

female (Foote 1945) to 3.0 males per female (Bailey 1972). Most indi­

cate a slight preponderance of males, but this could be due to the

greater mobility of the male increasing his chances of being captured

and thus sampled.

The mean weights of the Three Bar bobcats of 7.7 kg for males

and 5.0 kg for females are not significantly different (t = 2.77, df 4,

P >.05). However, the combined mean (6.3 kg) varies greatly from

Young's (1958) mean weight of 137 New Mexican bobcats of 9.6 kg., Rol­

lings' (1945) mean weight of 9.4 kg determined from 27 Minnesota bob­

cats, Progulske's (1952) mean for 117 Appalachian bobcats of 8.4 kg

and Pollack's (1949) mean of 8.3 kg from 113 New England bobcats. My

24

6.3 kg combined mean is fairly close to Young's (1958) mean weight of

100 Montana bobcats of 7.7 kg, Foote's (1945) weight from 376 Vermont

cats of 7.2 kg and Young's (1958) 6.5 kg derived from 79 California

bobcats. The range of values represented shows no trend toward larger

size in more boreal climates — a refutation of Bergmann's rule. How­

ever, in general that rule holds closely only for small homeotherms for

which thermal conductance is a major factor in thermoregulation. Lar­

ger homeotherms frequently use behavioral and physiological mechanisms

to circumvent the rule (Gordon 1972; Schmidt-Nielsen 1975)» which is

apparently the case with bobcats.

Diet and Prey Availability

I found rodent remains most frequently in the Three Bar bob­

cats' scats on both an annual basis (frequency of occurrence .665) and

during each of the bimonthly samples, V/oodrats predominated (47.8 per­

cent of the bobcat's rodent diet) and half as many heteromyids were

present (23*9 percent of the rodents consumed). These were the only

genera that had remains in bobcat scats throughout the year. In my

sample the presence of heteromyids, pocket gophers, white-footed mice

(Peromyscus spp.) and northern grasshopper mice (Onychomys leucogaster)

(if eaten) may all be biased low. Murie (1946) pointed out that

smaller rodents tend to be underestimated in scat analysis. I found

gophers and white-footed mice infrequently in bobcat scats during the

winter and early spring, but neither seasonal sample is large enough to

use as the basis for a significant conclusion. The occurrence of

25rodents in bobcat scats does not vary significantly among the six bi­

monthly samples (X^ = 1.&5, df 5» P >.05).

Bobcats appear to have found and eaten rock squirrels (Spermo-

philus variegatus) throughout the year, but only rarely consumed

Harris' antelope squirrel (Ammospermophilus harrisi). I qualitatively

observed that both were generally abundant on the study area throughout

the year. Perhaps a difference in their habits or in bobcat preference

for them accounts for the apparent disparity in selection of them as

prey items.

Along with rodents, lagomorphs form the major mammalian prey

of the bobcat on the Three Bar. Lagomorph remains appear in 37.5 per­

cent of the scats I analyzed and do not vary significantly (x^ = 0.90,

df 5» P >.05) among the six bimonthly samples.

Deer remains appear in 2.8 percent of the scats of Three Bar

bobcats, but of the five scats that I collected which contained deer

remains, four came from Rocky Point Ridge in mid-July. I speculate

that these may all represent one deer carcass being eaten as carrion.

The other scat containing deer remains was weatherbeaten when I found

it on Peters Mountain in late November. That scat contained a small

hoof which I believe was from a fawn, probably killed in early October.

Because white-tailed deer (Odocoileus virginianus) occur at the higher

elevations of the study area, I cannot verify that the fawn was a mule

deer. A single scat contained javelina hair, although I could not

determine the status (carrion, piglet, adult) of the javelina involved.

Albert Le Count (personal communication 1976) says that mule

deer are born on the Three Bar during the first three weeks of August

26

and herd composition counts suggest that fawns are not preyed upon sig­

nificantly after they are approximately three weeks old. Sowls (1966) reported that June, July and August are the peak months of javelina

parturition. My data indicate that bobcats do not prey upon the young

of these species during their first critical weeks — at least not

during a year of abundant rodent and lagomorph populations.

I found only one scat containing skunk (Mephitis spp.) remains.

The canid remains in one scat were hair and a nail attached to a meta­

tarsal, which I could only identify to genus. The bones appeared to

be of approximately coyote size.

Egg shell fragments appeared in bobcat scats from April through

August. I could not determine what types of egg shells they were, but

Gambel's quail (Lophortyx gambelli) are prevalent on the area, are

ground nesters and thus are vulnerable to predation by bobcats. Bent

(1932) quoted Willard as saying that quail eggs may be found from early

May into August, and Gorsuch (193*0 indicated that quail eggs may be

laid in April. Quail were exceptionally numerous during the fall of

1975 and appeared to have hatched two or possibly three clutches of

eggs that year, making the presence of eggs in August a likelihood.

The greater than average precipitation during the winter of 1976 might

have induced early nesting in the quail in 1976, and these early nests

may account for some of the eggs bobcats ate in April of that year.

Bird remains which I found in scat samples could have been

nesting quail, but I could not identify them positively. The single

snake was also unidentifiable

My dietary data fits the general pattern established in other

bobcat studies. Major studies represented in Tables 6, 7 and 8 indi­

cate diets in the western, southern and northeastern states respec­

tively. The trend is toward greater predation on rodents and some

lagomorphs in the west, increased consumption of lagomorphs in the

south and a greater dependence on lagomorphs and deer in the northeast.

This pattern optimizes the bobcat’s energy balance by yielding more

nutrients per kill (and associated hunting effort) in the more boreal

regions where the critical season (winter) is more severe and a more

efficient hunt to kill energy ratio is required to maintain homeo­

stasis.

I intended for the monthly rodent samples to show the general

trend of the rodent population and thus the availability of rodents to

bobcats as prey. These samples show an increase from July to November

(frequency .053 to .237) followed by a decline into May (.083). Sig-pnificant differences (X = 62.06, df 10, P <.05) exist between the

numbers of rodents I trapped each month. All rodents trapped are

listed in Dickerman (1955) and Cockrum (i960) as present on the Three Bar, although they name others that I did not find.

Various authors (Chew and Butterworth 1964; Beatley 1969;

Bradley and Mauer 1971; Van de Graaff and Baida 1973; Reichman and

Van de Graaff 1975) have alluded to a relationship between the inges­

tion of green vegetation and reproduction in desert rodents. The re­

lation of precipitation to desert plant production is obvious, so I

attempted to correlate the frequencies of rodents I trapped with the

27

Table 6. Percentages of occurrence of principle bobcat prey items — Western states. — Stomachanalyses except as noted.

Prey

JonesPers.Obs.

Ariz.n=176a

Young1958

W. U.S.n=399C

Sperry1958U.S.

n=3538b

Leach and Frazier 1953 Calif. n=l66

McLean1934

Calif.n=156

Gashwiler et al. I960

Utah & Nev. n=134c

JuvePers. Com.

1975Ariz.n=71d

Rodent 66.5 51.4 46 - - - 49.0Cricetid - 7.9 28 - - - -Neotoraa 31.8 - - 19.9 19.9 10.4 -

Microtus — - - 21.7 22.4 6.7 -Peromyscus ( 2.8) - - - - 6.5 -Heteromyid 15-9 - 5 18.0 - - -Thomomys 5.1 - - 14.5 5.1 - -Sciurid - - 10 10.3 16.7 - -Erethizon - ( 4.9) - - - - -Lagomorph 37.5 36.6 45 25-9 15.4 59.6 8.2Odocoileus ( 2.8) - 5 6.0 8.3 29.8 -Sheep - 11.8 - - - - -Unk. Bird ( 4.0) 9.5 - - 21.8 - 6.1Grouse - 5.2 - - - - -Egg Shell 10.2 - - - - - -

a. 1?6 scats.b. 70$ of Sperry's data from western states.c. 53 stomachs, 8l scats and intestines.d. U.S. Fish and Wildlife Serv., San Antonio.

Table ?• Percentages of occurrence of principle bobcat prey items — Southern states. —Stomach analyses except as noted.

Prey

Kight 1962

S • Car. n=317a

Davis1955Ala.

n=239

Progulske1952

Va. & N.Car. n=231b

Fritts1973Ark.n=150

Korschgen1957Mo.n=46

Rodent - - 21.2 -Neotoma - - - 5.3 -Microtus - - 11.1 - -Peromyscus - 5.4 - 5.3 8.7Sigmodon 38.9 11.3 - 6.7 -Sciurid - - - 22.0 -Sciurus - 9.2 24.9 16.0 17.4Marmota - - 5.1 - -Lagomorph 27.3 63.2 57.3 38.7 52.2Odocoileus - 10.5 17.2 7.3 -Didelphis - - 6.5 8.7 -Unk. Bird 11.0 - 6.9 6.6 8.7

a. 317 scats.b. 124 scats, 37 stomachs, 50 intestinal tracts.

Table 8. Percentages of occurrence of principle bobcat prey items — Northeastern states. —Stomach analyses except as noted.

Prey

Stevens1971N.H.n=599

Pallack1949

New .Eng. n=458a

Erickson1955Mich.n=385b

Hamilton & Hunter 1939 Ver. n=l40

Westfall1936Me.n=88

Rollings1945Minn.n=50

Cricetid ( 4.7) - 11.4 25.0 - -

Microtus - 12.4 - - 6.8 -Peromyscus - - - - 6.8 -Sciurid 14.0 - 6.0 9 .3 - -Sciurus 9.9 7.5 - - - -Tamiasciurus - - - - 12.5 -Erethizon ( 4.8) 12.1 9 .9 8.6 11.4 20Lagomorph 28.7 - 25.7 22.1 - -Lepus 12.4 28.3 - - 21.6 52Sylvilagus 15.4 28.0 - - — -Odocoileus 18.5 30.2 47.0 22.9 40.9 44Mephitis - - - 5.0 - -Insectivore - - - - - 10Unk. Bird (4.3) - 6.0 - - -Bonasa - - - 8.6 6.8 -

a. 208 stomachs.b. 213 stomachs, 44 intestines, 44 scats, 84 prey remains.

monthly precipitation (tabulated in Appendix C, from Le Count, personal

communication 1976) one and two months prior. The correlation with the

prior month's precipitation is positive but not significant (r = .241,

df 10, P >.05), as is the correlation with two month's prior precipi­

tation (r = .417, df 10, P >.05). When I pool the rodent availability

frequencies into the same bimonthly groupings in which I collected bob­

cat scats and attempt to correlate them with bimonthly pooled precipi­

tation figures for the month prior to and first month of the given

rodent sample, the correlation is high and almost significant (r = .732,

df 5t P >.05). I suspect my sample size is not quite large enough to

show significant rodent response to precipitation and the resulting

availability of green vegetation.

The lagomorph census indicates a Sylvilagus : Lepus ratio of

approximately 9:1. The absence of grazing on the area during the past

28 years has probably created a denser ground cover, favoring the cot­tontail. The census results show a zenith in August (1.04) and nadir

in November (0.32), with significant differences between the monthly

counts (X = 65.92, df 11, P < .05). Hunger ford, Lowe and Madsen (1974)

recorded reproductive activity in californicus and £5̂ auduboni in

southern Arizona as peaking during January, February, March and July-

August, and at the nadir during Ocotboer, November, December. These

periods of reproductive activity generally agree with the population

trend I found. They attributed increases in rabbit reproduction to in­

creases in precipitation, although Sowls (1957) found no correlation

between precipitation and jS. auduboni reproduction in southern Arizona.

31

32I attempted to correlate lagomorph frequencies from my census with one

and two months' prior precipitation but both coefficients Eire negative

and non-significant (r = -.222, r = -.388, df 11, P >.05). No apparent

relationship between lagomorph population levels and precipitation

exists on the Three Bar. However, my census data might be biased low

from October through February during the quail hunting season, because

quail hunters tend to hunt along roads. Those rabbits that they kill

while hunting quail thus represent a disproportionately greater per­

centage of my sample lagomorphs than are leaving the population due to

naturEil attrition.

Latham (1951) indicated that the availability of prey items is

the primary determinant of a predator's diet. I attempted to correlate

the frequencies of rodent and lagomorph remains in bobcat scats with

their respective frequencies of availability to test this hypothesis.

Figures 4 and 5 graphically represent these relationships. As would

be expected, since both availabilities vary significantly but neither

of the scat remains do, neither correlation coefficient is significant

(rodents r = -.616, df 5, P >.05; lagomorphs r = .074, df 5, P >.05). The selection of lagomorphs as prey appears to be density independent

(at the densities existing during the study). The relatively high

negative correlation of rodent availability with consumption indicates

that bobcats are capable of procuring rodents for food in great numbers

even when rodent densities are comparatively low (but still equal to

or above the minimum densities encountered during the study).The correlation between rodent and lagomorph consumptions by

bobcats is negative (r = -.565, df 5, P >.05) and although not

RODENTS AVAILABLE RODENTS CONSUMED.800

.750

.700

-.650

-.600

-.550

.500JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY

FigureM O N T H

4. Monthly rodent availability and consumption by bobcats on the Three Bar Wildlife Area, Arizona,

f

RO

DE

NT

S C

ON

SU

ME

D

(RO

DE

NT

S/S

CA

T)

LAGO

MORP

HS AVAILABLE (LA

GOMO

RPHS

/KM)

LAGOMORPHS AVAILABLE H I LAGOMORPHS CONSUMED

I.SOn 1.40

1.30

1.2 0 -

1.1 0 -

1.00

0 . 9 0 -

0 . 8 0

0 . 7 0 H

0.60

0.50

0 . 4 0 -

0 .30-1

420

k.4IO .400

-.390

.380

-.370

-.360

-.350

.340

-.330

-.320

- . 3 1 0

300

MONTH

Figure 5* Monthly lagomorph availability and consumption by bobcats on the Three Bar Wildlife Area, Arizona.

%

LAGOMORPHS CONSUMED (LAGOMORPHS/SCAT)

35significant, is high enough to suggest that to some degree increased

predation pressure on one group is accompanied by decreased pressure

on the other. The two groups may be acting as mutual buffers.

In general, bobcats on the Three Bar do not seem to be strictly

opportunistic predators. If they were, they would prey extensively on

the (relatively) most abundant prey available. Bobcats appear instead

to be efficient enough at rodent- and rabbit-catching to make it ener­

getically feasible for them to hunt for other than the most abundant

prey. Griffiths (1975) has suggested that such energy-maximizing (as

opposed to number-maximizing) in prey selection can be beneficial to a

selective predator when prey densities exceed a specific minimum

threshhold, which they apparently did on the Three Bar during the

course of my study.

Population Trend Techniques

The data from the census route were questionable the first time

and negative the second time. Although Young (1958) documented the

bobcat's curiosity and fondness for catnip, they do not utilize roads

extensively in their nocturnal travels as coyotes do, and do not seem

to be curious enough to regularly come to census stations baited with

the attractants I used.

I assumed that with a (short term) stable bobcat population the

results of the scat transects would probably be fairly homogeneous.

The samples are significantly different (x^ = 18.0, df 9, P <.05)

apparently due to weather, changing bobcat activity patterns and pos­

sibly seasonal differences in bobcat behavior. The greater number of

36scats that I found in February and March may have been the result of

increased marking behavior associated with mating or it may have been

random. Replications of these transect collections in future years

while monitoring the Three Bar bobcats' population trend could deter­

mine the value of this technique.

APPENDIX A

STANDARD MEASUREMENTS OF BOBCATS

37

38

Table Al. Standard measurements of bobcats trapped on the Three Bar Wildlife Area, Arizona. — Linear measurements in mm, weights in kg.

Date Number Sex Age Length Tail Ear Foot Weight

10/29 252 M Adult 928 134 76 170 7.7

1/30-2/9 253 F Adult 8?6 147 70 164 6.8

2/3 257 M V. Old 850 52 30 161 8.0

2/3 258 M Old 908 157 67 185 7.32/8 259 F Old 833 129 71 154 4.5

3 A 8 255 F Young 702 114 74 152 3.6

APPENDIX B

STANDARD MEASUREMENTS OF RODENTS

39

Table Bl. Means and standard deviations of standard measurements of rodents trapped on the Three Bar Wildlife Area, Arizona. — Weights in.g, linear measurements in mm.

Species N Weight Sw Length Si Tail St Ear se Foot Sf

Dipodomysmerriami 109 46.2 6.8 244.8a 13.0 147.9a 9.8 13.8 1.4 38.2 1.5Peromyscusboylei 60 22.7 4.3 179.7b 14.5 97.1b 10.7 17.9 1.8 20.1 1.8

Neotomaalbigula 52 167.0 38.5 297.1 33.3 130.4 15.6 28.0 2.3 32.1 1.6

Perognathusbaieyi 46 29.9 5.2 202.7c 20.4 116.4c 15.8 10.5 1.0 26.4 2.0

Onychomysleucogaster 26 26.0 2.9 142.0 7.3 50.4 3.8 17.0 1.5 20.8 1.1

Ammospermophilus harrisi 10 118.4 13.3 222.6 12.0 67.7 8.6 11.9 1.9 36.8 1.8

a. N = 107.b. N = 54.c. N = 42.

s

APPENDIX C

MONTHLY PRECIPITATION

41

42

Table Cl. Monthly precipitation on the Three Bar Wildlife Area,Arizona, 1975-1976.

Month Precipitation

April 1.68

May 0.36

June 0.00

July 7.14

August 5.03September 6.60

October 0.00

November 8.23

December 3.53January 2.82February 8.69

March 0.79April 1.55

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46

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