OIKOS 94: 236–249. Copenhagen 2001

Resource utilization and interspecific relations of sympatricbobcats and coyotes

Jennifer C. C. Neale and Benjamin N. Sacks

Neale, J. C. C. and Sacks, B. N. 2001. Resource utilization and interspecific relationsof sympatric bobcats and coyotes. – Oikos 94: 236–249.

We used scat analysis and radiotelemetry to characterize use of foods and habitats bysympatric bobcats and coyotes, and evaluated these in the context of spatial andtemporal relationships to assess the potential for, and evidence of, interspecificcompetition. Bobcats and coyotes exhibited broad and overlapping diets. However,diets of the two predators differed in the relative contributions of small and largeprey, with bobcats consuming relatively more rodent and lagomorph biomass andcoyotes consuming relatively more ungulate biomass. Consumption among rodentprey species was highly correlated between bobcats and coyotes, indicating noevidence of prey partitioning within this group. Habitat selection by the twopredators differed slightly at the landscape scale but not within home ranges. Bobcatsand coyotes occupied small, overlapping home ranges, such that the likelihood ofinterspecific encounters (direct or indirect) was high. Bobcats displayed slight avoid-ance of overlapping coyote core areas during coyote reproductive seasons (winter andspring), when coyotes are typically most territorial (toward conspecifics), but dis-played slight attraction during times of year when coyotes were not engaged inreproductive activities. Relative to coyotes, which were strongly nocturnal, dielactivity patterns of bobcats were more diurnal and variable. However, activitypatterns were not inversely correlated. Overall, these predators appeared to useresources independently and we found little evidence of negative interactions. Differ-ences in resource use by bobcats and coyotes appeared to relate to fundamental nichedifferences as opposed to competition-related resource partitioning.

J. C. C. Neale and B. N. Sacks, Dept of En�ironmental Science, Policy and Manage-ment, Uni�. of California, Berkeley, CA 94720, USA (present address: JCCN: Dept ofEn�ironmental Toxicology, One Shields A�enue, Uni�. of California, Da�is, CA 95616,USA [jcneale@ucda�is.edu]; BNS: John Muir Inst. of the En�ironment, One ShieldsA�enue, Uni�. of California, Da�is, CA 95616, USA).

Interspecific competition is thought to play an impor-tant role in structuring communities (Schoener 1982)and, according to theory, should be especially impor-tant in the top trophic level (Hairston et al. 1960,Oksanen et al. 1981). Empirically, the importance ofcompetition among terrestrial carnivores has beendifficult to assess due to the paucity of intensive fieldstudies (Palomares and Caro 1999). Accordingly, weinvestigated resource utilization and interspecific inter-actions of two mesopredators with greatly overlappinggeographic ranges (Nowak 1991), the coyote (Canis

latrans) and the bobcat (Lynx rufus), the putative infe-rior competitor (Litvaitis 1992).

Relationships between these two species have beendifficult to assess. Because bobcats and coyotes havesimilar life requisites, they might be expected to com-pete where they co-occur. Evidence suggestive of com-petition between bobcats and coyotes includes decliningbobcat populations in many parts of North America(Knowlton and Tzilkowski 1979) associated with rangeexpansion of the coyote (Litvaitis and Harrison 1989,Parker 1995), an inverse relationship between popula-

Accepted 19 March 2001

Copyright © OIKOS 2001ISSN 0030-1299Printed in Ireland – all rights reserved

OIKOS 94:2 (2001)236

tion indices of bobcats and coyotes (Linhart andRobinson 1972), apparent increases in bobcat densitiesfollowing population reduction of coyotes (Nunley 1977,Henke and Bryant 1999), and reports of coyote-causedbobcat mortality (Anderson 1986, Knick 1990). Otherstudies, however, reported positively related patterns ofabundance of bobcats and coyotes (Schnell et al. 1985)or no relationship (Lovell et al. 1998, Main et al. 1999),suggesting a variable or ambiguous relationship.

The major niche dimensions that competitors may useto partition life requisites in short supply are habitat andfood (Schoener 1986). Contingency models of resourcepartitioning suggest that when resources are abundant,animals should be maximally specialized in use of foodor habitat type (Schoener 1974a); morphological differ-ences are particularly effective in allowing specializationby food size (Schoener 1974b). As food becomes limit-ing, breadth of food and habitat types used shouldincrease. Unfortunately, theoretical predictions relatedto competition and resource utilization have largelyignored spatial relationships, which add another layer ofcomplexity to, and interact with, interspecific dynamics.Assessing resource use at the population level andwithout respect to space or time can generate ambiguousfindings with respect to competitive mechanisms, espe-cially when only one niche axis is examined, as in manycomparative studies of carnivore food habits. Spatiallyexplicit and temporal patterns of resource overlap andseparation can aid interpretation.

We investigated use of food and habitat types as wellas spatial and temporal relationships between sympatricbobcats and coyotes. Our study took place in northernCalifornia during July 1994–December 1995, shortlyafter the end of a severe drought (1987–1992; Sacks1998) when resources appeared superabundant (Neale1996) and predator populations likely were approachingequilibrium levels. Densities of bobcats (Neale 1996) andcoyotes (Sacks 1996) at our study site approximated themaxima reported for these species (Camenzind 1978,Hall and Newsom 1978, Jachowski 1981, Andelt 1985,Lembeck 1986), increasing the likelihood of chanceencounters. To explore resource use in this context, we(1) characterized diets of the two predators through fecalanalysis utilizing two approaches – frequency of occur-rence and estimated biomass consumption – to compareuse of foods, (2) investigated habitat selection at both thelandscape and within-home range scales using ra-diotelemetry, (3) assessed spatial relationships on multi-ple scales, and (4) compared diel activity patterns.

Methods

Study area

The study area was centered on the 21-km2 HoplandResearch and Extension Center (HREC; 39°00�N,

123°05�W) in Mendocino County, California, USA. Thissite was located in the Coast Range mountains in theRussian River drainage and had a primarily southwestaspect; topography was hilly to semi-rugged, with eleva-tions ranging 150–915 m. Vegetation consisted of amosaic of four principal types: chaparral, mixed ever-green-deciduous forest (forest), annual grassland (grass-land) and woodland (Murphy and Heady 1983). Coverdensity was greatest in chaparral and forest and least ingrassland. The climate was characterized by cool, wetwinters and warm, dry summers. Numerous potentialprey of coyotes and bobcats occurred on the site includ-ing two lagomorph species, 13 rodent species, black-tailed deer (Odocoileus hemionus), and various birds,reptiles, and invertebrates (Neale 1996). In addition towild prey, between 900 and 2500 domestic sheep wereregularly maintained on the site. Coyotes on the studyarea suffered high mortality due to routine removal toreduce sheep depredation (Sacks et al. 1999a). Bobcatsgenerally were not associated with sheep kills (Neale etal. 1998) and none were removed during our study.

Food habits

Scats of bobcats and coyotes were collected bi-weeklyfrom 21 transects (0.5 km in length) established through-out the study area (57% of scats), as well as opportunis-tically when found fresh (43%). Scats were assigned topredator species based primarily on size and shape(Murie 1954, Danner and Dodd 1982) as well as odorand other sign. Inspection of scats collected from knownindividuals from traps or during radiotracking confi-rmed our classification criteria. Approximately 10% ofcarnivore scats were of ambiguous origin and werediscarded. Scats were oven-dried, placed in nylon bags,washed in an automatic clothes washer, and tumble-dried, as described by Neale (1996). Hair, teeth, andbone were identified using reference skins, skulls, skele-tons, hair keys, and photomicrographs (e.g., Mayer1952, Glass 1973).

Although frequency of occurrence (the percent ofscats containing each food item) is commonly used toquantify diets of carnivores, this measure does notaccurately reflect the proportional consumption of fooditems in carnivore diets. For example, frequency ofoccurrence tends to overestimate vegetative food items(Andelt and Andelt 1984), underestimate large mam-malian prey (Weaver 1993), and can be biased withrespect to detection of prey in scats due to differencesamong rodent prey in recovery rates of teeth and hair(Kelly 1991). Therefore, to more accurately assess foodhabits of these predators, we estimated biomassconsumed.

Fecal analysis was performed according to specifica-tions of Kelly’s (1991) residue-weight model, which

OIKOS 94:2 (2001) 237

utilized correction factors derived from feeding trials toinfer amount consumed from food remains. Dependingon the scat contents, analysis involved separating andweighing hair, teeth, and bones, including count andweight of each tooth type present, as well as estimatingpercent volume for each food item in each scat (Kelly1991). We used Program SCAT (Version 1.5.1) toestimate biomass consumption represented by scat con-tents and to calculate the proportion of total biomassrepresented by each food item. This program did notinclude a correction factor for reptiles or vegetation.However, based on visual estimates of percent volume,reptile remains did not contribute substantially to preybiomass for either predator. Occurrence of manzanita(Arctostaphylos spp.) berries was high in scats of coy-otes (Neale 1996); we therefore calculated a correctionfactor for manzanita (1.85 g fresh berry consumed per1 g residue) based on the number of berries representedper gram residue and the average weight of a freshberry. Items found in scats but excluded from analysesincluded grass and occasional orchard fruits, as well asvery rare occurrences of moles (Scapanus latimanus)and various carnivores.

We compared bobcat and coyote food niches basedon overall and seasonal diets, with seasonal periodsdesignated as follows: summer (Jul.–Sep.), fall (Oct.–Dec.), winter (Jan.–Mar.), and spring (Apr.–Jun.).Rather than pool scats across seasons to estimate over-all diets (which would have resulted in biases towardseasons with larger scat samples), we averaged acrossseasonal values to generate overall values. We calcu-lated measures of dietary breadth (B) and food nicheoverlap (�) based on Pianka (1973):

B=1��� pi

2�,

�=� (piqi)��� pi

2 � qi2,

where pi is the proportion of food item i in the diet ofpredator p, and qi is the proportion of food item i in thediet of predator q. In this study, a maximum of 13categories were available such that breadth ranged from1 (only 1 food item taken) to 13 (all food items taken,in equal proportions). The index of overlap ranges from0 (complete dissimilarity) to 1 (complete similarity).Overlap indices should be based on resource categoriesat least as fine as those perceived by the predators(Krebs 1989), thus we categorized prey to the specieslevel whenever possible (Greene and Jaksıc 1983).

For comparative purposes, we also calculated overallfrequency of occurrence and relative frequency of oc-currence (the latter values were expressed as percent ofall occurrences, to allow direct comparison withbiomass) as well as total and seasonal breadth measuresand overlap indices based on frequency of occurrence.

An additional 226 coyote scats were analyzed usingonly frequency of occurrence due to the extensive timerequirements of biomass estimation.

Radiotelemetry study

Bobcats and coyotes were captured using No. 3, pad-ded-jaw leghold traps (Woodstream Corp., Littitz, PA,USA) or homemade snares (coyotes only) with stops toprevent strangulation. Devices were set along roads,ridges, fences, and drainages throughout HREC. Bob-cats were sedated with a mixture of ketamine hydro-chloride and xylazine hydrochloride (10 mgketamine+1.6 mg xylazine/kg body mass). Capturedanimals were radiocollared, weighed, measured, andexamined for reproductive and general condition (Neale1996, Sacks et al. 1999b). Animal care and handlingprocedures were approved by the Animal Care and UseCommittee, Univ. of California, Berkeley (ProtocolcR190-0496). We conducted radiotelemetry of resi-dent predators throughout the day and night 5–7 d perweek using stationary and mobile (hand-held) units asdescribed previously (Neale et al. 1998, Sacks et al.1999b), locating most individuals at least once per day.Average telemetry error was estimated at 146 m, with95% of errors �356 m (Sacks 1996).

We used program CALHOME (Kie et al. 1996) tocalculate annual and seasonal 65% and 90% adaptivekernel (AK) isopleths and annual 95% minimum con-vex polygons (MCP). The AK ranges reflected intensityof use (Worton 1989); the 65% and 90% isoplethscorresponded to core areas and home ranges, respec-tively (Sacks et al. 1999b). The MCPs were used tobound areas of availability (e.g., of habitat) because, incontrast to AKs, MCPs were relatively insensitive todispersion of locations (i.e., clumped, uniform, or ran-dom). We determined annual home ranges for residentbobcats and coyotes with �100 radiolocations andmonitored during �9 months of the study. Homerange sizes of bobcats did not vary significantly by sex(Neale 1996) and thus were pooled for estimation. Maleand female coyotes of a territorial pair used virtuallyidentical areas; thus we chose one range (the female’s)to represent the territory. Seasonal core areas and homeranges were calculated for territorial female coyotes(range=42–306 locations per season, X� �SD=126�69).

Habitat selectionWe assessed habitat selection, i.e., use relative toavailability, by bobcats and coyotes at two spatialscales. We used a vegetation map derived from LAND-SAT imagery (Fox et al. 1997) in conjunction with ageographic information system (GIS; ARCVIEW 3.0a,Environmental Systems Research Institute, Redlands,CA, USA) to classify habitats into the four major types

238 OIKOS 94:2 (2001)

on our study area: chaparral, forest, grassland, andwoodland. To compare habitat selection of the twocarnivores at the level of home range establishment(i.e., landscape), we calculated habitat composition ofthe annual 95% MCPs using the GIS. We used individ-ual home ranges as the sample unit and calculated 95%Bonferroni confidence intervals on arcsine transformedmean proportions (Zar 1984: 239).

Next, we tested for habitat selection within homeranges by comparing the proportion of each individu-al’s radiolocations in each habitat type (observed) tothe proportion of that habitat in the individual’s MCP(expected). Previous studies comparing habitat use ofbobcats and coyotes (e.g., Major and Sherburne 1987,Litvaitis and Harrison 1989) have used the radioloca-tion as the sample unit. Although this has been com-mon practice in habitat selection analyses (Neu et al.1974, Byers et al. 1984), the use of radiolocationsinstead of individuals as the sample unit amounts topseudoreplication (Hurlbert 1984), which in this partic-ular application (i.e., for territorial species) is especiallyproblematic (Litvaitis et al. 1994). To avoid this prob-lem, we calculated habitat selection indices for eachindividual separately, for each habitat type, as log-transformed ratios (+1; Zar 1984: 238–239) of ob-served to expected proportions of radiolocations minuslog(2) plus 1 (the last two terms made a selection indexof 1 correspond to an observed-to-expected ratio of 1).We calculated 95% Bonferroni confidence intervals ofselection indices for each habitat during wet (winter–spring) and dry (summer– fall) seasons.

Spatial relationshipsWe investigated overlap of adjacent bobcat and coyoteannual 90% AK home ranges. We used the proportionof a bobcat home range overlapped by a neighboringcoyote home range as a measure of interspecific spatialoverlap (Bradley and Fagre 1988). Quantification ofhome range overlap is useful as a descriptor and mayindicate the likelihood of encounters. However, withthe possible exception of adjacent but non-overlappinghome ranges with shared boundaries (indicative ofstrong interspecific territoriality), this metric is toocoarse to indicate anything about avoidance (or attrac-tion) behavior.

Previous studies (Major and Sherburne 1987, Lit-vaitis and Harrison 1989) have attempted (and failed)to detect avoidance or attraction between coyotes andbobcats using a modification of the nearest neighboranalysis (Clark and Evans 1954, Keenan 1981) wherebyseparation distances of paired simultaneous locations ofbobcats and coyotes with adjoining or overlappinghome ranges are compared to randomly paired loca-tions of the same two individuals. We used this tech-nique (using locations separated by �1 h) inpreliminary analyses and similarly found no avoidance.However, if the distance at which a bobcat would alter

its course due to the presence of a coyote is short (e.g.,�150 m) relative to radiotelemetry error (which seemslikely, especially in dense vegetation or rugged topogra-phy), this technique would be extremely insensitive.Further, the distance between two ‘‘simultaneous’’ loca-tions that are widely separated in time (up to 4 h;Litvaitis and Harrison 1989) is unlikely to differ in anymeaningful way from that between randomly pairedlocations.

Therefore, to determine whether bobcats avoidedcoyotes, we compared use versus availability of coyotecore areas by spatially overlapping bobcats. We chosethe core area of coyotes because this was the mostintensively used portion of the home range, and there-fore where territorial behavior would be expected to bemost apparent. [We also conducted the analyses usingcoyote home ranges; results were similar and therefore,to avoid duplication, were not presented here.]Availability of coyote core areas was calculated foreach bobcat, corresponding to the proportion of abobcat’s annual 95% MCP overlapping core areas ofresident female coyotes. Because coyotes shifted theircore areas seasonally, these were calculated separatelyfor each season. Use was indicated by proportions ofradiotelemetry locations falling inside coyote cores. Ra-tios of observed (use) to expected (available) propor-tions of locations within coyote core areas were used tocalculate selection indices as described above (under‘‘Habitat selection’’). Selection indices were calculatedfor bobcats with �20 locations in a season. Canidstend to be most territorial towards conspecifics duringbreeding (winter) and pup-rearing (spring) (Jaeger et al.1996); it is unknown whether interspecific territorialitybetween coyotes and bobcats also reflects similar sea-sonality. Therefore, we tested for seasonal differences inbobcat selection indices for coyote core areas usinganalysis of variance.

Acti�ityTo evaluate overlap between bobcats and coyotes intime, we examined diel activity patterns during wet anddry seasons. Activity (active, inactive, or ambiguous)was assessed at the time of radiolocation, and wasinferred from amplitude fluctuation and bearing shift(Andelt 1985, Major and Sherburne 1987) or pulse-ratevariation for a subset of animals (5 bobcats, 1 coyote)that wore motion-sensitive transmitters (Telonics, Inc.,Mesa, AZ, USA). Environmental conditions such ashigh winds can influence amplitude fluctuation. There-fore, we only evaluated activity for locations in whichwe were confident the animal was active or inactive(55% of locations; Sacks 1996). We calculated propor-tions of these locations coded as active during eight 3-hdiel periods. Only animals with �20 activity-codedlocations in a diel period were included in calculationsof diel period averages.

OIKOS 94:2 (2001) 239

Table 1. Proportional biomass (percent of the estimated total biomass of prey consumed represented by each food item) andfrequency of occurrence (percent of scats containing each food item) of food itemsa in bobcat and coyote scats, Jul. 1994–Dec.1995. For direct comparison with proportional biomass, the relative frequency of occurrence of food items (number ofoccurrences of a food item/total number of occurrences of all items in sample, expressed as percent) is given in parentheses.Values for composite groups are left-justified for clarity.

CoyoteBobcat

biomass (%) freq. of occ. (%)freq. of occ. (%) biomass (%)n=226 scats n=537 scats,n=226 scats, n=311 scats

865 occurrences416 occurrences

Ungulatea 18.1 16.7 (9.1) 41.2 (25.6)59.1Deer 12.6 23.4 (14.5)11.0 (6.0) 32.4Sheep 18.7 (11.6)4.9 4.8 (2.6) 23.7

Lagomorphb 23.3 9.0 (5.6)27.8 (15.1) 6.0Rodenta 42.3 (26.3)57.2 75.95 (41.3) 30.0

Squirrelc 4.7 3.9 (2.5)11.6 (6.3) 3.2Woodrat 10.3 (6.4)18.2 26.3 (14.3) 10.0Pocket gopher 7.7 8.2 (5.1)11.2 (6.1) 3.0Kangaroo rat 3.6 5.5 (3.0) 1.1 2.0 (1.2)Chipmunk 0.2 0.6 (0.4)1.2 (0.6) 0.1Vole 15.4 (9.6)14.0 25.4 (13.8) 7.7Miced 5.8 8.6 (5.3)20 (10.9) 3.3

Bird 1.1 11.1 (6.0) 7.8 (4.8)0.6Insect 0.2 11.7 (7.3)8.5 (4.6) 0.4Reptile n/a 17.2 (9.3) 7.8 (4.8)n/aManzanita 0.0 2.4 (1.3) 33.7 (20.9)3.9

a ‘‘Ungulate’’ and ‘‘rodent’’ categories include unidentified large and small mammals, respectively.b Syl�ilagus bachmani and Lepus californicus.c Sciurus griseus and Spermophilus beecheyi.d Peromyscus sp. and Reithrodontomys megalotis.

Results

Food habits

Most of the biomass consumed by both predators wasrepresented by three mammalian taxa (ungulates, ro-dents, and lagomorphs; Table 1). The two predatorsdiffered in their relative consumption of large and smallprey, with small mammals dominating the bobcat dietand ungulates dominating the coyote diet (Fig. 1). Theslope of the regression line in Fig. 1 indicated that forcoyotes the proportion of total biomass composed byrodents was 54% that of bobcats. Within the rodentcategory, however, relative ranking of species was quitesimilar for bobcats and coyotes (revealed by the closefit of points about the trend line for rodents). Based onbiomass, overall niche breadth was 6.71 for bobcatsand 4.91 for coyotes; overall niche overlap was 0.63.Based on frequency of occurrence, overall nichebreadth was 8.84 for bobcats and 8.35 for coyotes;overall niche overlap was 0.62.

Prey selection by bobcats and coyotes changed overtime, but was not generally linked to season per se (i.e.,showing similarity between successive summers orfalls). Ungulate consumption by bobcats, althoughmuch lower, roughly paralleled that of coyotes overtime (Fig. 2A). Bobcats displayed a decreasing trend inrodent consumption and an increasing trend in lago-morph consumption, whereas no consistent trends wereevident for coyote consumption of these prey (Fig. 2B,C). Seasonality of manzanita berries in coyote scats was

apparent in frequency of occurrence data, whichshowed manzanita berries frequently consumed by coy-otes during summer and fall seasons; in contrast, man-zanita berries composed only a small proportion of thebiomass consumed in all seasons (Fig. 3). Bobcat sea-sonal niche breadth, based on biomass, paralleled bob-

Fig. 1. Consumption of ungulate, rodent, and lagomorph preyby coyotes versus bobcats, expressed as proportion of theestimated total fresh biomass of prey consumed, HoplandResearch and Extension Center, July 1994–December 1995.Filled circles represent rodent species, open circles representdeer and sheep. Rodent regression line intercept was con-strained to the origin.

240 OIKOS 94:2 (2001)

cat-coyote niche overlap and both decreased during thelatter part of the study; no pattern was evident incoyote niche breadth (Fig. 4A). Seasonal breadth andoverlap measures based on frequency of occurrenceshowed no obvious trends (Fig. 4B).

Radiotelemetry study

We captured and monitored 13 coyotes and 11 bobcats.Bobcats were categorized by sex and estimated age classat capture, and weights were calculated for adult fe-males (X� �SE=5.03�0.07 kg, n=3), subadult males(5.78�0.38 kg, n=5), and adult males (7.70+0.36 kg,n=3). Average weights (�SE) of coyotes were 9.77(�0.34) kg for females and 11.36 (�0.63) kg formales. We obtained 2770 radiolocations of bobcats and4498 radiolocations of coyotes. Of the radiocollared

Fig. 2. Proportion of prey biomass consumed by bobcats andcoyotes consisting of (A) ungulate, (B) rodent, and (C) lago-morph prey during six seasons, Hopland Research and Exten-sion Center, July 1994–December 1995. Seasonal sample sizesfor bobcat and coyote scats, respectively: 34, 52 (summer1994); 20, 52 (fall 1994); 76, 53 (winter 1995); 49, 51 (spring1995); 27, 51 (summer 1995); and 20, 52 (fall 1995).

bobcats, there was one death (cause undetermined)during the study period. All bobcats appeared to be ingood condition at initial capture, subsequent captures,and during visual observations.

Habitat selectionHabitat composition of the 95% MCP was similar forbobcats and coyotes, although coyote home rangestended to include more grassland and less forest thandid bobcat home ranges (Fig. 5). Habitat selection

Fig. 3. Seasonal use of manzanita berries by coyotes, asmeasured by occurrence in scats versus biomass consumed,Hopland Research and Extension Center, July 1994–Decem-ber 1995.

OIKOS 94:2 (2001) 241

within home ranges was very similar for bobcats andcoyotes in all seasons (Fig. 6). Grassland tended to beused less than expected (based on availability) by bothcarnivores, but this was significant only for coyotes inwinter–spring 1995. Forest was marginally selected forby coyotes during winter–spring 1995 as was woodlandfor bobcats.

Spatial relationshipsAnnual home range size of bobcats averaged (�SE)8.7�1.3 km2 (90% AK) and 9.8�1.5 km2 (95% MCP).Coyote annual home ranges averaged 4.4�0.9 km2

(90% AK) and 5.2�1.1 km2 (95% MCP). An averageof 16% (range=2–46%) of a bobcat’s home range wasoverlapped by each neighboring coyote home range,and most bobcat home ranges were overlapped by �2(radiocollared) coyote territories. Coyote territorieswere mutually exclusive.

Fig. 5. Habitat composition of home ranges of bobcats (n=11) and coyote pairs (n=4), expressed as proportions of the95% minimum convex polygon consisting of each of fourmajor habitat types, Hopland Research and Extension Center,July 1994–December 1995. Error bars correspond to 95%Bonferroni confidence intervals.

Fig. 4. Seasonal estimates of dietary breadth for bobcats andcoyotes, and bobcat–coyote food niche overlap, based on (A)biomass consumption and (B) frequency of occurrence of fooditems, Hopland Research and Extension Center, July 1994–December 1995.

Bobcat use of coyote core areas, as indicated byselection indices, differed seasonally (F=3.40, df=5,24, P=0.018). In particular, bobcats avoided coyotecore areas most during winter and spring (Fig. 7).Although sample sizes were too small (n=3 largemales) to include bobcat body size as a factor instatistical analyses, only small bobcats appeared toavoid coyote cores during winter, whereas all bobcatsappeared to avoid coyote core areas during spring (Fig.8).

Acti�ityRelative to coyotes, diel activity of bobcats was vari-able, both within and among seasons (Fig. 9). Whereascoyotes were more consistently nocturnal, bobcats wererelatively less active during 0300–0559 h in both sea-sons for which data were collected for this diel period.Coyotes were generally least active during 1200–1759h. Diel activity patterns of bobcats and coyotes werenot negatively correlated in any season (r=0.11, P=0.11, summer– fall 1994; r=0.06, P=0.90, winter–spring 1995; r=0.26, P=0.26, summer– fall 1995).

Discussion

Food habits

Food use represents a primary mode of resource parti-tioning between two ecologically similar species. AtHREC, overall food niche overlap of bobcats andcoyotes was moderate when compared with values fromother carnivore studies based on the same index (Je-drzejewska and Jedrzejewski 1998). Dietary differenceswere primarily associated with prey size. Whereas small

242 OIKOS 94:2 (2001)

Fig. 6. Habitat selection indicesfor bobcats (open circles) andcoyotes (closed circles) duringsummer– fall 1994 (A, B),winter–spring 1995 (C, D), andsummer– fall 1995 (E, F),Hopland Research andExtension Center, July1994–December 1995. Values�1=positive selection,�1=negative selection, 1=noselection. Sample sizes were 7,8, and 5 bobcats, and 4, 4, and3 coyotes in chronologicalorder. Error bars correspond to95% Bonferroni confidenceintervals.

mammals were the principal prey of bobcats, ungulatescomprised the bulk of prey biomass for coyotes. Incontrast to bobcats, which tend to be solitary (Bailey1974, Major and Sherburne 1987), coyotes often huntin pairs or groups, which likely facilitates predation onungulates (Gese et al. 1988, Gese and Grothe 1995,Sacks et al. 1999b). Body size is often an importantconstraint on prey size selection as well (Gittleman1985). Whereas bobcats tend to be slightly smaller thancoyotes on average throughout their ranges (Young1958, Nowak 1991), bobcats on our study area weresubstantially smaller than coyotes (roughly half themass on average), which also may have hindered theirability to kill ungulates.

Another difference in the diets of bobcats and coy-otes in this study was in consumption of vegetation.Because this difference is characteristic of canids andfelids generally (Nowak 1991), it clearly reflected differ-ences in fundamental niches of bobcats and coyotes.

Interestingly, although most studies of bobcat and coy-ote food habits have concluded that fruit in the coyotediet but not bobcat diet was a major seasonal nichedifference (e.g., Small 1971, Toweill and Anthony 1984,Witmer and DeCalesta 1986, Major and Sherburne1987, Litvaitis and Harrison 1989, DiBello et al. 1990),the omnivorous status of the coyote contributed little todifferences between bobcat and coyote diets in thisstudy. Although manzanita occurred at a high fre-quency in coyote scats seasonally, it contributed littlebiomass. Thus, estimates of coyote niche breadth andbobcat–coyote overlap based on frequency of occur-rence were biased by undue influence of manzanitaberries.

Food niches of bobcats and coyotes became lesssimilar over the course of our study, based on preybiomass. This pattern, as well as the decreasing trend inbobcat dietary breadth, may have resulted from thepartial replacement of rodent species by lagomorphs

OIKOS 94:2 (2001) 243

(single taxon) in the bobcat diet. The tight relationshipbetween bobcat and coyote consumption within rodentspecies (Fig. 1) suggested that these predators perceivedrodents as a group, which they differentiated fromlagomorphs and ungulates by size. When we calculatedthe seasonal niche breadth indices using lumped preycategories (i.e., rodent, lagomorph, ungulate), bobcatbreadth did not decrease over time. Bobcats may haveshifted from rodents to lagomorphs as a prey-switchingresponse to changing relative abundances of these prey(Murdoch 1969), although we did not quantify preyabundance.

Habitat selection

Habitat segregation may occur independently of inter-specific interactions. For example, felids often rely ondense understory cover to facilitate their stalk andambush style of predation, in contrast to the openpursuit typical of canids (Kleiman and Eisenberg 1973);thus cover and open habitat types might be expected tobe selected by bobcats and coyotes, respectively. In thisstudy there was a slight tendency for bobcat homeranges to include more forest and less grassland thancoyote home ranges. Further, bobcat home rangestended to be located at higher elevations, spread alongthe primary mountain ridge, suggesting some degree ofselection for features associated with these areas, suchas steep hillsides and rugged, rocky terrain.

Within their home ranges bobcats and coyotes dis-played nearly identical habitat selection, suggesting thatdifferences at the landscape scale were not related tointerspecific interactions. The slight negative selection

of grassland by both predators was consistent withprevious findings for bobcats (May 1981, Koehler andHornocker 1991), but was uncharacteristic of coyotes,which tend to selectively use such open habitats (e.g.,Major and Sherburne 1987). Negative selection ofgrassland by coyotes in this study was likely relatedprimarily to avoidance of humans (Sacks 1996). Sheepintensively grazed much of the grassland habitat in ourstudy and density of grassland rodents may have beenrelatively low in this habitat as a result (Hayward et al.1997), further reducing its attractiveness to coyotes(and bobcats).

Spatial relationships

The potential for chance encounters between bobcatsand coyotes, and hence interference, on the study areawas high due to high densities, small home ranges, andhigh interspecific home range overlap. Whereas ex-ploitation competition, by definition, requires that aresource (usually food) be limiting, behavior associatedwith interference competition may be present regardlessof current resource levels. For example, agonistic be-havior and interspecific killing could be cued by detec-tion of a particular species rather than being causedproximately by resource limitation, although such aresponse could be the evolutionary consequence of pastresource competition.

Bobcats displayed some avoidance of the most inten-sively used parts of coyote home ranges during winterand spring, which coincided with coyote breeding andpup-rearing, when coyotes tend to be most territorialtoward conspecifics. Core avoidance during winter(coyote breeding) was only apparent for small bobcats,whereas large and small bobcats avoided coyote coresduring spring (pup-rearing), when these areas corre-sponded to den sites, which were probably activelydefended. These findings were consistent with otherstudies indicating that small bobcats (females andyoung males) are more vulnerable to agonistic interac-tions with coyotes (Anderson 1986, Litvaitis 1992).

We suspect that the observed spatial avoidance ofcoyote cores by bobcats in this study reflected indirect(e.g., avoiding coyote scent) as opposed to direct (i.e.,being chased) interactions. We found no evidence thatbobcats were injured or killed by coyotes. Only oneradiocollared bobcat died during our study and, al-though we recovered the carcass too long after death todetermine the cause, we found no evidence of attack byanother carnivore (e.g., tooth punctures in the skele-ton). In addition to the bobcats captured in our study,many others were captured before and after the studyduring attempts to capture coyotes for other research(e.g., Sacks et al. 1999a, b); none of these bobcats hadinjuries indicative of coyote attacks.

Fig. 7. Selection indices of observed versus expected use ofoverlapping coyote core areas by bobcats during six seasons,Hopland Research and Extension Center, July 1994–Decem-ber 1995. Values �1=positive selection, �1=negative se-lection, 1=no selection. Sample sizes were 4, 5, 8, 7, 4, and 2bobcats in chronological order. Error bars correspond to 95%Bonferroni confidence intervals.

244 OIKOS 94:2 (2001)

Fig. 8. Space use by femaleand small male bobcats (A, B)and large male bobcats (C, D)with respect to coyoteterritories during winter (A, C)and spring (B, D) 1995,Hopland Research andExtension Center, January1995–June 1995. Seasonalbobcat locations (dots) andannual 95% MCPs (lines;female ranges have dashedline) are overlaid on seasonalcoyote territories (shadedpolygons; darker shading incore areas).

Activity

Partitioning of resources in time is rare relative topartitioning by food or habitat types (Schoener 1974a).Temporal segregation among carnivores is usually notan effective means of partitioning resources per se,because shared resources generally are not renewedwithin a diel period, and thus exploitation competitionis not alleviated (Jaksıc et al. 1981). However, temporalspacing may reflect a response to agonistic interactionsas with spatial segregation. Toweill (1986) reporteddifferent patterns of activity of bobcats and coyoteswhich he speculated helped to minimize interspecificcontact.

At HREC, although bobcats displayed some avoid-ance of coyotes in space, we found no evidence of acorresponding avoidance in time. Activity patterns ofbobcats and coyotes were not negatively correlated andalthough the two predators displayed different dielpatterns of activity, these differences did not coincidewith seasons when spatial avoidance was most pro-nounced. In comparison, transient coyotes, which dis-played strong spatial avoidance of residents at ourstudy site (Sacks et al. 1999b), displayed diel activitypatterns opposite those of resident coyotes (Sacks1996). Nocturnal activity of resident coyotes was prob-ably due primarily to high human exploitation. Duringthe year previous to this study, no removal of coyotes

OIKOS 94:2 (2001) 245

was attempted and coyote activity patterns were lessnocturnal (Sacks 1996). Bobcats suffered no exploita-tion and therefore did not share this pressure for noc-turnality. Diurnal activity seems to be generally moretypical of unexploited populations of bobcats (Kitch-ings and Story 1978) and coyotes (Gipson and Sealan-der 1972, Andelt 1985, Kitchen et al. 2000).

Bobcat–coyote niche relationships

Taken together, our findings indicate that bobcats andcoyotes used food and habitat resources independentlyof each other. The avoidance of coyote cores by bob-cats during some seasons provided limited evidence ofnegative relations. However, the lack of evidence of

physical harm or of temporal avoidance suggested thatsuch behavior was not especially important, despitegenerally high densities of the two predators. It seemslikely that prey size differences and/or abundance offood alleviated competition between these twocarnivores.

Other studies of bobcats and coyotes conducted inenvironments with mild, relatively stable climates hadsimilar results (Witmer and DeCalesta 1986, Bradleyand Fagre 1988). In these studies, as in ours, densitiesof both predators were high, interspecific home rangeoverlap was extensive, and bobcats and coyotes usedfoods and habitats similarly. These authors did notreport any evidence of interspecific avoidance in spaceor time, agonistic interactions, or coyote-caused bobcatinjury or mortality.

Fig. 9. Average diel activityof (A) bobcats and (B)coyotes, during summer– fall1994 (n=11 bobcats, 9coyotes), winter–spring 1995(n=8, 6), and summer– fall1995 (n=5, 3), HoplandResearch and ExtensionCenter, July 1994–December1995. Standard error bars andconnecting lines are notshown in summer– fall 1995due to small sample sizes andmissing data.

246 OIKOS 94:2 (2001)

In contrast, studies in harsh environments character-ized by long, severe winters, reported that bobcats andcoyotes occurred at relatively low densities and occu-pied large home ranges (Toweill 1986, Major and Sher-burne 1987, Litvaitis and Harrison 1989). Bobcats andcoyotes displayed moderate to extensive home rangeoverlap but because of large use areas, chance interspe-cific encounters were likely rare even in overlap areas.High overlap in one niche dimension (e.g., food use)was often related to low overlap in another (e.g., habi-tat use; Toweill 1986), indicating niche complementar-ity. Agonistic interactions included at least one bobcatkilled by coyotes in the Cascade Mountains of Oregon(Toweill 1986) and one bobcat killed in a trap bycoyotes in eastern Maine (Litvaitis and Harrison 1989).Major and Sherburne (1987) working in western Mainereported no evidence of agonistic behavior, but believedthat exploitation competition for deer may have beenimportant, and presented evidence that bobcats were ingenerally worse condition during winter than coyotes.This may have reflected climatic stress rather thaninterspecific competition with coyotes, as the study areaoccurred in the northernmost boundary of the bobcatrange.

Thus, the importance of interspecific competitionbetween bobcats and coyotes seems generally low butperhaps greater in highly seasonal climates characteris-tic of northern/northeastern North America and moun-tainous regions of the western U.S. as compared tomild, stable climates of the southern and west-coastalregions. Although prey biomass tends to be lower innortherly regions, low prey biomass per se does notimply prey scarcity because predator biomass on aver-age tends to correspond to average prey biomass (e.g.,Knowlton and Gese 1995). However, in northern NorthAmerica resources regularly become limiting due toharsh winters and, in boreal regions, multiannual cyclesin abundance of primary prey provide additional peri-ods of prey scarcity (and abundance; Keith and Wind-berg 1978, O’Donoghue et al. 1998). In contrast,Mediterranean or semi-arid climates of western andsouthern North America tend to be more stable andpredator and prey populations are likely to be closer toequilibrium more of the time, such that prey are rarelyvery scarce (or abundant) relative to predatorabundance.

Acknowledgements – We thank M. M. Jaeger and HREC forsupporting this study. K. Blejwas, J. Dayton, J. Meisler, J.Poor, Jr., and T. Weller provided valuable field assistance. S.Ardley, J. Theade, E. Voight, and volunteers with the Univer-sity Research Expedition Program helped with scat collection.M. E. Jaeger, K. Finn and C. Wu assisted with scat analysis.G. Trehey and C. Brooks provided GIS expertise and satelliteimages. Funding and equipment were provided in large partby the USDA National Wildlife Research Center throughcooperative agreements with the U. of Calif. at Berkeley (No.12-34-74-0235-CA), and with the Div. of Agriculture andNatural Resources of the U. of Calif. (No. 12-34-74-0224-CA).

Additional support was provided by the Dept of Environmen-tal Science, Policy, and Management, the A. Starker Leopoldendowed chair, and a graduate fellowship (JN) at the U. ofCalif. at Berkeley. We thank V. Bakker, N. Belfiore, K.Blejwas, R. Brock, K. Kauhala, R. Lewison, M. Meyer, S.Riley, T. Schoener, A. Suarez, and D. VanVuren for construc-tive review of the manuscript.

ReferencesAndelt, W. F. 1985. Behavioral ecology of coyotes in south

Texas. – Wildl. Monogr. 94.Andelt, W. F. and Andelt, S. H. 1984. Diet bias in scat

deposition-rate surveys of coyote density. – Wildl. Soc.Bull. 12: 74–77.

Anderson, E. M. 1986. Bobcat behavioral ecology in relationto resource use in southeastern Colorado. – Ph.D. disserta-tion, Colorado State Univ., Fort Collins, CO.

Bailey, T. N. 1974. Social organization in a bobcat population.– J. Wildl. Manage. 38: 435–446.

Bradley, L. C. and Fagre, D. B. 1988. Movements and habitatuse by coyotes and bobcats on a ranch in southern Texas.– Proc. Annu. Conf. Southeast. Assoc. Fish Wildl. Agen-cies 42: 411–430.

Byers, C. R., Steinhorst, R. K. and Krausman, P. R. 1984.Clarification of a technique for analysis of utilization-availability data. – J. Wildl. Manage. 48: 1050–1053.

Camenzind, F. J. 1978. Behavioral ecology of coyotes on theNational Elk Refuge, Jackson, Wyoming. – In: Bekoff, M.(ed.), Coyotes: biology, behavior and management. Aca-demic Press, pp. 267–294.

Clark, P. J. and Evans, F. C. 1954. Distance to nearestneighbor as a measure of spatial relationships in popula-tions. – Ecology 35: 445–453.

Danner, D. A. and Dodd, N. 1982. Comparison of coyote andgray fox scat diameters. – J. Wildl. Manage. 46: 240–241.

DiBello, F. J., Arthur, S. M. and Krohn, W. P. 1990. Foodhabits of sympatric coyotes, Canis latrans, red foxes,Vulpes �ulpes, and bobcats, Lynx rufus, in Maine. – Can.Field-Nat. 104: 403–408.

Fox, L. III, Bonser, G. L., Trehey, G. H. et al. 1997. A wildlifehabitat map and database for the ORCA (Oregon-Califor-nia) Klamath Bioregion derived from Landsat imagery,version 1.0.

Gese, E. M. and Grothe, S. 1995. Analysis of coyote predationon deer and elk during winter in Yellowstone NationalPark, Wyoming. – Am. Midl. Nat. 133: 36–43.

Gese, E. M., Rongstad, O. J. and Mytton, W. R. 1988.Relationship between coyote group size and diet in south-eastern Colorado. – J. Wildl. Manage. 52: 647–653.

Gittleman, J. L. 1985. Carnivore body size: ecological andtaxonomic correlates. – Oecologia 67: 540–554.

Gipson, P. S. and Sealander, J. A. 1972. Home range andactivity of the coyote in Arkansas. – Proc. Annu. Conf.Southeast. Assoc. Game Fish Comm. 26: 82–95.

Glass, B. P. 1973. A key to the skulls of North Americanmammals. – Dept Zoology, Oklahoma State Univ., Still-water, OK.

Greene, H. W. and Jaksıc, F. M. 1983. Food-niche relation-ships among sympatric predators: effects of level of preyidentification. – Oikos 40: 151–154.

Hairston, N. G., Smith, F. E. and Slobodkin, L. B. 1960.Community structure, population control, and competi-tion. – Am. Nat. 94: 421–425.

Hall, H. T. and Newsom, J. D. 1978. Summer home rangesand movements of bobcats in bottomland hardwoods ofsouthern Louisiana. – Proc. Annu. Conf. Southeast. As-soc. Fish Wildl. Agencies 30: 427–436.

Hayward, B., E. Heske, J. and Painter, C. W. 1997. Effects oflivestock grazing on small mammals at a desert cienaga. –J. Wildl. Manage. 61: 123–129.

OIKOS 94:2 (2001) 247

Henke, S. E. and Bryant, F. C. 1999. Effects of coyoteremoval on the faunal community in western Texas. – J.Wildl. Manage. 63: 1066–1081.

Hurlbert, S. H. 1984. Pseudoreplication and the design ofecological field experiments. – Ecol. Monogr. 54: 187–211.

Jachowski, R. L. 1981. Proposal to remove the bobcat fromAppendix II of the Convention on International Trade inEndangered Species of Wild Fauna and Flora. – FederalRegister 46: 45652–45656.

Jaksıc, F. M., Greene, H. W. and Yanez, J. L. 1981. Theguild structure of a community of predatory vertebratesin central Chile. – Oecologia 52: 171–175.

Jaeger, M. M., Pandit, R. K. and Haque, E. 1996. Seasonaldifferences in territorial behavior by golden jackals inBangladesh: howling versus confrontation. – J. Mammal.77: 768–775.

Jedrzejewska, B. and Jedrzejewski, W. 1998. Predation invertebrate communities: the bialowieza primeval forest asa case study. – Springer-Verlag.

Keenan, R. J. 1981. Spatial use of home range among redfoxes (Vulpes �ulpes) in south-central Ontario. – In:Chapman, J. A. and Pursley, D. (eds), Proceedings of theWorldwide Furbearer Conference, Frostburg, MD, 1980.Worldwide Furbearer Conference, Inc., pp. 1041–1067.

Keith, L. B. and Windberg, L. A. 1978. A demographicanalysis of the snowshoe hare cycle. – Wildl. Monogr.58: 1–70.

Kelly, B. T. 1991. Carnivore scat analysis: an evaluation ofexisting techniques and the development of predictivemodels of prey consumed. – M.S. thesis, Univ. Idaho,Moscow, ID.

Kie, J. G., Baldwin, J. A. and Evans, C. J. 1996. Calhome:a program for estimating animal home ranges. – Wildl.Soc. Bull. 24: 342–344.

Kitchen, A. M., Gese, E. M. and Schauster, E. R. 2000.Changes in coyote activity patterns due to reduced expo-sure to human persecution. – Can. J. Zool. 78: 853–857.

Kitchings, J. T. and Story, J. D. 1978. Preliminary studies ofbobcat activity patterns. – Proc. Annu. Conf. Southeast.Assoc. Fish Wildl. Agencies 32: 53–59.

Kleiman, D. G. and Eisenberg, J. F. 1973. Comparisons ofcanid and felid social systems from an evolutionary per-spective. – Anim. Behav. 21: 637–659.

Knick, S. T. 1990. Ecology of bobcats relative to exploita-tion and a prey decline in southeastern Idaho. – Wildl.Monogr. 108.

Knowlton, F. F. and Tzilkowski, W. M. 1979. Trends inbobcat visitations to scent-station survey lines in westernUnited States, 1972–1978. – Bobcat Res. Conf. Proc.,Natl. Wildl. Fed. Sci. Tech. Ser. 6: 8–12.

Knowlton, F. F. and Gese, E. M. 1995. Coyote populationprocesses revisited. – In: Rollins, D., Richardson, C.,Blankenship, T. et al. (eds), Coyotes in the southwest: acompendium of our knowledge. Symposium Proc., Dec.13–14, 1995, San Angelo, TX, pp. 1–5.

Koehler, G. M. and Hornocker, M. G. 1991. Seasonal re-source use among mountain lions, bobcats, and coyotes.– J. Mammal. 72: 391–396.

Krebs, C. J. 1989. Ecological methodology. – Harper andRow.

Lembeck, M. 1986. Long term behavior and population dy-namics of an unharvested bobcat population in SanDiego County. – In: Miller, S. D. and Everett, D. D.(eds), Cats of the World: biology, conservation and man-agement. National Wildlife Federation, pp. 305–310.

Linhart, S. B. and Robinson, W. B. 1972. Some relativecarnivore densities in areas under sustained coyote con-trol. – J. Mammal. 53: 880–884.

Litvaitis, J. A. 1992. Niche relations between coyotes andsympatric Carnivora. – In: Boer, A. H. (ed.), Ecology

and management of the eastern coyote. Wildlife ResearchUnit, Univ. New Brunswick, pp. 73–85.

Litvaitis, J. A. and Harrison, D. J. 1989. Bobcat-coyoteniche relationships during a period of coyote populationincrease. – Can. J. Zool. 67: 1180–1188.

Litvaitis, J. A., Titus, K. and Anderson, E. M. 1994. Mea-suring vertebrate use of terrestrial habitats and foods. –In: Bookhout, T. A. (ed.), Research and managementtechniques for wildlife and habitats. The Wildlife Society,pp. 254–274.

Lovell, C. D., Leopold, B. D. and Shropshire, C. C. 1998.Trends in Mississippi predator populations, 1980–1995. –Wildl. Soc. Bull. 26: 552–556.

Main, M. B., Walsh, P. B., Portier, K. M. and Coates, S. F.1999. Monitoring the expanding range of coyotes in Flor-ida: results of the 1997–1998 statewide scent station sur-veys. – Fla. Field Nat. 27: 150–162.

Major, J. T. and Sherburne, J. A. 1987. Interspecific rela-tionships of coyotes, bobcats and red foxes in westernMaine. – J. Wildl. Manage. 51: 606–616.

May, D. W. 1981. Habitat utilization by bobcats in easternMaine. – M.S. thesis, Univ. Maine.

Mayer, W. V. 1952. The hair of California mammals withkeys to the dorsal guard hairs of California mammals. –Am. Midl. Nat. 48: 480–512.

Murdoch, W. W. 1969. Switching in general predators: ex-periments on predator specificity and stability of preypopulations. – Ecol. Monogr. 39: 335–354.

Murie, O. J. 1954. A field guide to animal tracks. –Houghton Mifflin.

Murphy, A. H. and Heady, H. F. 1983. Vascular plants ofthe Hopland Field Station, Mendocino County, Califor-nia. – Wasmann J. Biol. 41: 53–96.

Neale, J. C. C. 1996. Comparative resource use by sympatricbobcats and coyotes: food habits, habitat use, activity,and spatial relationships. – M.S. thesis, Univ. of Califor-nia, Berkeley, CA.

Neale, J. C. C., Sacks, B. N., Jaeger, M. M. and McCul-lough, D. R. 1998. A comparison of bobcat and coyotepredation on lambs in north-coastal California. – J.Wildl. Manage. 62: 700–706.

Neu, C. W., Byers, C. R. and Peek, J. M. 1974. A techniquefor analysis of utilization-availability data. – J. Wildl.Manage. 38: 541–545.

Nowak, R. M. 1991. Walker’s Mammals of the World. Vol.II, 5th edn. – Johns Hopkins Univ. Press.

Nunley, G. L. 1977. The effects of coyote control operationson non-target species in New Mexico. – Proc. GreatPlains Wildl. Damage Control Workshop 3: 88–110.

O’Donoghue, M., Boutin, S., Krebs, C. J. et al. 1998. Func-tional responses of coyotes and lynx to the snowshoehare cycle. – Ecology 79: 1193–1208.

Oksanen, L., Fretwell, S. D., Arruda, J. and Niemela, P.1981. Exploitation ecosystems in gradients of primaryproductivity. – Am. Nat. 118: 240–262.

Palomares, F. and Caro, T. M. 1999. Interspecific killingamong mammalian carnivores. – Am. Nat. 153: 492–508.

Parker, G. 1995. Eastern coyote: the story of its success. –Nimbus.

Pianka, E. R. 1973. The structure of lizard communities. –Annu. Rev. Ecol. Syst. 4: 53–74.

Sacks, B. N. 1996. Ecology and behavior of coyotes in rela-tion to depredation and control on a California sheepranch. – M.S. thesis, Univ. California, Berkeley, CA.

Sacks, B. N. 1998. Increasing prevalence of canine heart-worm in coyotes from California. – J. Wildl. Dis. 34:386–389.

Sacks, B. N., Blejwas, K. M. and Jaeger, M. M. 1999a.Relative vulnerability of coyotes to removal methods ona northern California ranch. – J. Wildl. Manage. 63:939–949.

248 OIKOS 94:2 (2001)

Sacks, B. N., Jaeger, M. M., Neale, J. C. C. and McCullough,D. R. 1999b. Territoriality and breeding status of coyotesrelative to sheep predation. – J. Wildl. Manage. 63: 593–605.

Schnell, G. D., Grzybowski, J. A., Hough, D. J. and McKenna,T. M. 1985. Evaluation of spatial patterning in Oklahomafurbearer populations. – Southwest. Nat. 30: 225–238.

Schoener, T. W. 1974a. The compression hypothesis and tempo-ral resource partitioning. – Proc. Natl. Acad. Sci. 71:4169–4172.

Schoener, T. W. 1974b. Resource partitioning in ecologicalcommunities. – Science 185: 27–39.

Schoener, T. W. 1982. The controversy over interspecific com-petition. – Am. Sci. 70: 586–595.

Schoener, T. W. 1986. Resource partitioning. – In: Kikkawa,J. and Anderson, D. J. (eds), Community ecology: patternand process. Blackwell, pp. 91–126.

Small, R. L. 1971. Interspecific competition among three speciesof Carnivora on the Spider Ranch, Yavapai Co., Arizona.

– M.S. thesis, Univ. Arizona.Toweill, D. E. 1986. Resource partitioning by bobcats and

coyotes in a coniferous forest. – Ph.D. dissertation, OregonState Univ.

Toweill, D. E. and Anthony, R. G. 1984. Ecology of an exploitedbobcat population in western Oregon. – Oregon Dep. Fishand Wildl. Job Completion Rep. Proj. W-80-R-1 jobs 3–6.

Weaver, J. L. 1993. Refining the equation for interpreting preyoccurrence in gray wolf scats. – J. Wildl. Manage. 57:534–538.

Witmer, G. W. and DeCalesta, D. S. 1986. Resource use byunexploited sympatric bobcats and coyotes in Oregon. –Can. J. Zool. 64: 2333–2338.

Worton, B. J. 1989. Kernal methods for estimating the utiliza-tion distribution in home range studies. – Ecology 70:164–168.

Young, S. P. 1958. The bobcat of North America. – Univ.Nebraska Press.

Zar, J. H. 1984. Biostatistical analysis, 2nd ed. – Prentice-Hall.

OIKOS 94:2 (2001) 249