COMPETITIVE INTERACTIONS BETWEEN COYOTES AND SAN JOAQUIN KIT FOXES

BRIAN L. CYPHER AND KENNETH A. SPENCER

Enterprise Advisory Services, Inc., P.O. Box 178, Tupman, CA 93276 Present address of KAS: Colorado State University,

Center for Ecological Management of Military Lands, Fort Hunter Liggett, CA 93928 Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021

Competitive interactions between coyotes (Canis latrans) and federally endangered San Joaquin kit foxes (Vuipes macrotis mutica) were investigated at the Naval Petroleum Re­ serves in California (NPRC) during 1984-1995. Coyotes and kit foxes used similar food items, indicating the potential for exploitative competition. Leporids were the primary prey for coyotes in all years, but small rodents were the primary prey for kit foxes in most years, although leporids were primary prey in other years. Coyotes were the main cause of mortality to kit foxes at NPRC, indicating that interference competition may be occur­ ring. Population trends of kit foxes appeared to be strongly i!1.fluenced by food availability, but competition from coyotes also may have affected population dynamics of kit foxes. Mechanisms employed by kit foxes, such as resource partitioning, greater dietary breadth, and year-round den use, may facilitate coexistence with coyotes. However, use of anthro­ pogenic food sources by coyotes may intensify competitive interactions during periods of low prey availability.

Key words: Vulpes macrotis mutica, kit fox, Canis tatrans, coyote, endangered species, competition, California

The San Joaquin kit fox (Vuipes macrotis tition. Coyotes also have been identified as mutica) is a federally endangered and Cal­ an important source of kit fox mortality ifornia tlueatened species occurring in the (Cypher and Scrivner, 1992; Disney and southern San Joaquin Valley and adjacent Spiegel, 1992; Ralls and White, 1995), and Salinas, Valley in California. Primary this mortality potentially constitutes inter­ threats to the continued existence of the kit ference competition. The objectives of this fox are loss, degradation, and fragmentation investigation were to detennine the extent of habitat due to agricultural, industrial, and of both exploitative and interference com­ urban development (United States Fish and petition between San Joaquin kit foxes and Wildlife Service, 1983). Pesticide use, coyotes, and to assess the effect of any predator control programs, and illegal competitive interactions on kit fox abun­ shooting and trapping may constitute sec­ dance. ondary threats. Competition from other predators, particularly coyotes (Canis la­ MATERIALS AND METHODS trans), also has been identified as a poten­ Study area.-Our investigation was conduct­ tial tlueat to kit faxes (Ralls and White, ed at the Naval Petroleum Reserves in California 1995). However, the extent and significance (NPRC) located ca. 42 Ian southwest of Bakers­ of competitive interactions between kit fox­ field, Kern Co. The NPRC is an area of active es and coyotes have not been determined. petroleum production and is comprised of the Coyotes apparently consume many of the 19,186-ha Naval Petroleum Reserve No. 1 same food items-used by kit foxes (Cypher (NPR-I) and the adjacent 12,173-ha Naval Pe M et aI., 1994; White et aI., 1995), and this troleum Reserve No.2 (NPR-2). Physiographi­ potentially constitutes exploitative compe- cally, NPR-l and NPR-2 each encompass anti-

Journal of Mammalogy, 79(1):204-214, 1998 204 February 1998 CYPHER AND SPENCER-COYOTE-KIT FOX COMPETITION 205 clinal ridges that are highly dissected by steep pare total and annual food-item use between kit draws and dry stream channels. Alluvial plains faxes and coyotes. So that data from coyotes and and flat valley lands surround the ridges. Ele­ foxes would be more comparable, food-item use vation ranges from 88 m to 473 m (Woodring et by kit foxes was determined using feces col­ al., 1932). Climate is characterized by hot dry lected on NPR-l during 1985-1988 and feces summers and cool wet winters with frequent fog. from both NPR-l and NPR-2 during 1989- Temperatures in summer often exceed 38°C and 1990. For this analysis, food items were cate­ seldom go below O°C in winter. Annual precip­ gorized as leporid, rodent, insect, or other. An­ Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 itation averages ca. 12 cm and occurs primarily nual and total dietary diversity were detennined as rain falling between November and April for both species by calculating a Shannon di­ (National Oceanic and Atmospheric Administra­ versity index (Brower and Zar, 1984). For each tion, 1992). year, a Student's t-test was used to test if diver­ Vegetation at NPRC is classified as either sity indices differed between kit foxes and coy­ Lower Sonoran Grassland (Twisselman, 1967), otes (Hutcheson, 1970). Hom's similarity index Valley Grassland (Heady, 1977), or Valley Salt­ (Hom, 1966) was used to estimate dietary over­ bush Scrub (Holland, 1986). Dominant shrubs lap between species. include desert saltbush (Atriplex polycarpa), Leporids were identified as an important food cheesebush (Hymenoclea salsola), and bladder­ item at NPRC for both kit foxes (Scrivner et aI., pod (lsomeris arborea). Herbaceous cover is 1987) and coyotes (Cypher et aI., 1994). Abun­ dominated by red brome (Bromus madritensis) dance of leporids was assessed annually at and red-stemmed filaree (Erodium cicutarium). NPRC beginning in 1984 by conducting line­ Food-item use.-Use of food items by coyo­ transect surveys (Harris, 1986). Surveys were tes and kit foxes was determined to assess ex­ conducted in summer (June) along 60 l.6-km ploitative competition. From 1985 to 1990, a transects established throughout NPRC. Annual coyote-reduction program was conducted at abundance of leporids was indexed by calculat­ NPRC in an effort to reduce predation on kit ing the number observed per km of transect. To faxes. Reduction was conducted on NPR-l from determine if abundance of leporids influenced 1985 to 1988 and on both NPR-l and NPR-2 their use by kit foxes and coyotes, annual fre­ from 1989 to 1990 (Cypher and Scrivner, 1992). quencies of occurrence of leporids in coyote This program resulted in the killing of 591 coy­ stomachs and kit fox feces was compared to an­ otes, which were taken in all seasons. Stomachs nual leporid indices using correlation analysis. were collected from 322 carcasses and frozen Frequencies of occurrence were arcsine-trans­ for analysis. Food habits of coyotes were deter­ formed (Zar, 1984) prior to analysis. mined by analysis of stomach contents (Cypher Kit fox mortality.-Sources and rates of mor­ et aI., 1994). tality of kit faxes were determined annually by Food habits of kit faxes were determined by monitoring fates of radiocollared kit faxes. Most analysis of feces. Feces were collected from fox­ adult faxes were collared (models L2B5, 300, es live-trapped during annual efforts to assess 95, and 80; Telonics, Inc., Mesa, AZ) during abundance, mortality rates, and reproductive live-trapping sessions conducted in summer success. Samples were collected in all seasons (July-August) and winter (Novetnber-January) except late winter-early spring (15 January-l to assess abundance. During these sessions, one May) when fox trapping was suspended to avoid wire-mesh box trap (37.5 by 37.5 by 105 cm) disturbing animals during parturition and early was placed in each quarter-section of NPR-2 and pup-rearing. Feces were oven-dried ~24 h and a 117-km2 study area on NPR-l, and set for 4 sent to a diagnostic laboratory (Global Ecosys­ consecutive nights. Traps were covered with tem Managers, Baton Rouge, LA) for analysis. tarps to provide protection from inclement Although highly disgestible items may have weather, baited with either canned mackerel or been more difficult to detect in feces compared pieces of road-killed leporid (not used after to stomachs, foods commonly consumed by kit 1981), and checked early the next morning. Cap­ foxes contain materials of low digestibility (e.g., tured foxes were weighed, aged (juvenile or hair, bone, exoskeleton) that were easily detect­ adult based on body mass and patterns of tooth ed in feces. eruption). ear-tagged, and inspected for injuries. Contingency-table analysis was used to com- All faxes were released at the capture site. Ju- 206 JOURNAL OF MAMMALOGY Vol. 79, No.1

venile foxes were collared (models 95, 80, and marks) were recorded. Annual indices of abun­ 2A; Telanies) during live-trapping conducted in dance were calculated by determining the pro­ spring (March-June) to assess reproductive suc­ portion of operable stations visited and multi­ cess of kit foxes. FOf this effort, traps were set plying by 1,000 (Harris, 1987; Roughton and at dens occupied by radiocollared adult females Sweeny, 1982). and pup-rearing dens identified by the presence Relationships between indices of abundance of prey remains, trampled vegetation, and sma11- of coyotes and kit foxes and between indices of sized tracks and feces (Morrell, 1972). coyote abundance and mortality rates of both Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 Radiocollared kit foxes were monitored diur­ adult and juvenile foxes were examined using nally several times per week. If a fox was mo­ correlation analysis. The relationship between tionless for 4 hours, the pulse rate emitted by mortality rates of kit foxes and the proportion of the radiocollar would increase (about double) mortalities caused by predators also was exam­ producing a mortality signal. Foxes with trans­ ined using correlation analysis. This relationship mitters emitting a mortality signal were recov­ was expected to be nonsignificant if mortality ered and necropsied to determine cause of death. attributable to coyotes was compensatory and Mortality from predators was identified by the positive if this source of mortality was additive. presence of tooth-puncture wounds, hemorrhag­ Correlation analysis was used to examine the ef­ ing around these wounds, and muscle and bone fect of leporid abundance on abundance for both injuries consistent with predator attacks (Wade coyotes and kit' foxes. Mortality rates and pro­ and Bowns, 1985). Monitoring of mortality of portions of mortalities caused by predators were kit foxes was suspended from 1991-1992 but arcsine-transformed to nonnalize data. Prelimi­ resumed in 1993. nary analyses indicated that if predation was ad­ Annual mortality rate for adult kit foxes was ditive, the relationship between mortality rates defined as the proportion of radiocollared foxes and predation rates would approximate a logistic that died < 1 year after foxes were collared. An­ function. Therefore, predation rates were log­ nual mortality rate for juvenile kit foxes was de­ transfonned prior to analysis (Zar, 1984). For all fined as the proportion of juveniles radiocollared statistical analyses, P values ::;0.05 were consid­ in the spring that died before 30 November of ered significant. their birth year. Juvenile foxes were considered to have reached adulthood and to have entered RESULTS the NPRC breeding population if they did not Food-item use.-Results of analyses of die or disperse off NPRC by 30 November. For stomach contents from 322 coyotes were both adult and juvenile foxes that died and for described by Cypher et al. (1994). In sum­ which the cause of death could be determined, the proportion of mortalities caused by predators mary, leporids (black-tailed jackrabbits, was determined annually. Lepus califomicus and desert cottontails, Population effects.-Abundance of kit foxes Sylvilagus audubonii) were the food items was indexed using capture data from the stan­ most frequently used by coyotes in each dardized live-trapping sessions conducted in year and for all years combined. Important winter. The number of individual foxes captured secondary items included kangaroo rats per 100 trap-nights was determined annually. (Dipodomys), other rodents (primarily Abundance of coyotes was indexed annually pocket gophers, Thomomys bottae and Cal­ beginning in 1985 by conducting scent-station ifornia ground squirrels, Spermophilus surveys in spring (February-March). Twenty beecheyi), livestock, birds, insects, and re­ survey lines were established with each line con­ fuse. Leporid occurred most frequently in sisting of 10 scent-stations spaced at O.5-Ian in­ the diet of coyotes from 1985-1988, but tervals along roads. Scent-stations were con­ structed by clearing vegetation and debris from other items, consisting primarily of live­ a l_m2 circular area, sifting a thin layer (ca. 2 stock, birds, and refuse, occurred most fre­ mm) of fine dirt over the area, and placing a quently in 1989-1990 (Fig. la). synthetic fatty-acid attractant disk in the center. From 1985 to 1990,449 feces of kit fox­ Stations were visited the next morning and any es were examined. Items identified in feces sign of visits by coyotes (e.g., tracks, feces, roll included leporids, kangaroo rats, San Joa- February 1998 CYPHER AND SPENCER-COYOTE-KIT FOX COMPETITION 207

• Leporid • Rodent ~ Insect 0 Other '" (a) COYOTE 100 - (b) KIT FOX

00 00 -

8c 8c ~, '" ,~ "

0 Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 0 8 0 " 0 " ] ." " '" " , n , I.r ,~ ~ n ~ 1985 1985 1987 1988 1989 1990 1985 1985 1987 1988 1989 1990 Year Year FIG. I.-Use of food item categories by a) coyotes (Canis latrans-Cypher et al., 1994) and b) San Joaquin kit foxes (Vulpes macrotis mutica) at the Naval Petroleum Reserves in California, 1985- 1990. quin pocket mice (Perognathus inomatus), pers), Rodents occurred most frequently in pocket gophers, California ground squirrels, diets of kit foxes in all years except 1990 San Joaquin antelope squirrels (Ammosper­ (Fig. 1b). mophilus nelsoni), deer mice (Peromyscus Use of food items by coyotes and kit fox­ maniculatus), western harvest mice (Rei­ es differed over all years combined (X 2 = throdontomys "megalotis), grasshopper mice 91.12, dj ~ 3, P < 0.01) and in 1986 (X' (Onychomys torridus), kit foxes, domestic ~ 11.25, dj ~ 3, P ~ 0.01), 1988 (X' ~ sheep (Ovis aries), roadrunners (Geococcyx 16.16, d.f ~ 3, P < 0.01), 1989 (x' ~ californianus), unidentified birds, unidenti­ 53.03, dj ~ 3, P < 0.01), and 1990 (X' ~ fied snakes, unidentified fish, beetles (most­ 17.59, dj ~ 3, P < 0.01), and approached ly Eleodes), Jerusalem crickets (Gryllacri­ significance in 1985 (X' ~ 6.49, dj ~ 3, P didae), grasshoppers (Acrididae), and re­ = 0.09). Use of food items was not differ­ fuse (e.g., string, burlap, plastic). ent in 1987 (X' ~ 6.08, dj ~ 3, P ~ 0.11). Kangaroo rats occurred most frequently Shannon diversity indices (Table 1) were in diets of kit foxes from 1986 to 1989 and higher for kit faxes in 1985 (t ~ -2.52, P in the overall diet, but leporids were the < 0.02) and 1990 (t ~ -2.62, P < 0.02) most common item in diets in 1985 and but higher for coyotes in 1989 (t = 2.15, P 1990. Important secondary items included < 0.05). Diversity indices were not differ­ other rodents (primarily pocket mice and ent in 1986 (t ~ 0.34, P > 0.05), 1987 (t San Joaquin antelope squirrels) and insects ~ 0.34, P > 0.05), or 1988 (t ~ 0.14, P > (primarily Jerusalem crickets and grasshop- 0.05), Hom's similarity indices indicated

TABLE I.-Annual indices of dietary diversity (Shannon index) and dietary similarity (Horn's index) for coyotes (Caris latrans) and San Joaquin kit foxes (Vulpes macrotis mutica), Naval Petro­ leum Reserves in California, 1985-1990.

1985 1986 1987 1988 1989 1990 Total Shannon diversity index Coyotes 0.5004 0.7079 0.7274 0.7717 0.7799 0.5283 0.7744 Kit foxes 0.7109 0.6839 0.6972 0.6274 0.6996 0.6967 0.7111 Horn's similarity index 0.74 0.81 0.79 0.76 0.83 0.61 0.85 208 JOURNAL OF MAMMALOGY Vol. 79, No. I

6 20 140 ~Leporids .....- ...' •...... - ... - Kit Foxes 120 5 I ... -'I! I \ ," ...•... Coyotes ,V" f !I'\ 100 I'" \ 0 I'" \ l-i \ so ~

"i \ .. Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 ~... /.: 60 ;;- /~ , I: Co v·.'---. '/ ~ ..... -.,.\ ,/.: 40 "'" '} / .. \"." / \ .f /-" 20

0 1984 1965 1986 1987 1986 1989 1990 1991 1992 1993 1994 1995 Year FIG. 2.-Abundance indices of Iepo rids. coyotes (Canis latrans), ap.d San Joaquin kit foxes (Vulpes macrotis mutica) at the Naval Petroleum Reserves in California, 1984-1995. that diets of coyotes and kit foxes were least venile kit foxes that died prior to 30 No­ similar in 1990; indices for other years were vember ranged from 50.0 to 100%, and the relatively high and generally similar (Table mean annual mortality rate was 79.8 ± 1). 4.5% (Table 2). The annual proportion of From 1984 to 1995. abundance of lepor­ mortalities of juveniles caused by predators ids at NPRC varied from 0.4-5.1/km of ranged from 50.0 to 100%, and the mean transect (Fig. 2). Frequency of occurrence annual proportion was 83.2 ± 4.7% (Table of leporid in kit fox scats was directly re­ 2). lated to leporid abundance (r ~ 0.66, d,f. ~ Although bobcats (Felis rufus) were 11, P = 0.02). However, frequency of oc­ present on NPRC, predation on kit foxes currence of leporid in coyote stomachs was assumed to be primarily caused by coy­ from 1985 to 1990 varied independently of otes. Bobcats can cause significant mortal­ leporid abundance (r ~ 0.29, d,f. ~ 5, P ~ ity among kit foxes (Disney and Spiegel, 0.57). 1992) and likely were responsible for some Kit fox mortality.-From 1980 to 1994 mortalities at NPRC. However, bobcats (excluding 1991 and 1992), mortality rates were only rarely observed or recorded at of kit foxes were detennined from 306 ra­ scent stations suggesting that their abun­ diocollared foxes. The annual proportion of dance was low compared to coyotes. adult foxes that died within 1 year of being Population effects.-From 1984 to 1995, collared ranged from 30.0 to 84.0%, and the the number of individual kit foxes captured mean (±SE) annual mortality rate was 61.0 per 100 trap-nights ranged from 1.9 in 1991 ± 5.2% (Table-2). The annual proportion of to 17.5 in 1994 (Fig. 2). From 1985 to mortalities of adults caused by predators 1995, coyote scent-station indices ranged ranged from 50.0 to 100%, and the mean from 21.9 in 1992 to 135.0 in 1986 (Fig. annual proportion was 75.8 ± 7.7% (Table 2). During this period, indices of abundance 2). Only one juvenile kit fox was radiocol­ for kit foxes and coyotes were not signifi­ lared in 1995, precluding analysis of mor­ cantly correlated (r ~ 0.50, d,f. ~ 10, P ~ tality rates. For the remaining years, rates 0.12), but the power of the test was only were detennined from 177 radiocollared ju­ moderate (0.67) and the trends were gen­ venile foxes. The annual proportion of ju- erally similar. Mortality rates for both adult February 1998 CYPHER AND $PENCER-COYOTE-KIT FOX COMPETITION 209

TABLE 2.-Annual mortality and predation rates for adult and juvenile San Joaquin kit foxes (Vulpes macrotis mutica) at the Naval Petroleum Reserves in California, 1984-1994 (kitfix mortality was not monitored in 1991 and 1992).

Adult kit foxes Juvenile kit foxes y,,,, n' Mortality rateb Predation rate" n Mortality rate Predation rate 1980 2. 0.32 0.80 I. 0.72 0.67

1981 26 0.31 0.67 16 0.69 0.89 Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 1982 37 0.57 0.71 19 0.63 1.0 1983 33 0.73 0.78 29 0.86 0.74 1984 53 0.76 0.85 22 0.91 0.79 1985 21 0.76 0.92 6 0.83 0.50 1986 12 0.67 0.50 9 0.67 0.67 1987 25 0.84 1.0 10 l.00 0.83 1988 9 0.78 1.0 17 0.88 1.0 1989 3 0.33 0 10 0.50 1.0 1990 23 0.52 1.0 7 1.00 1.0 1993 19 0.58 1.0 14 0.91 0.90 1994 17 0.77 0.64 I' • Number of radiocollared kit foxes monitored. b Proportion of adult foxes dying within 360 days of collaring and proportion of juvenile foxes dying before 30 November. c Proportion of kit fox mortalities due to predators. d Because only one juvenile fox was monitored in 1994, this year was not included in analyses. and juvenile kit foxes also varied indepen­ diate competItlon for food resources. Al­ dently of indices of abundance of coyotes though coyotes and kit foxes use many of (adult: r ~ 0.60, dj. ~ 7, P ~ 0.11: juve­ the same food items, they apparently use nile: r ~ 0.02, d.! ~ 7, P ~ 0.96). The them in different proportions. Leporids correlation between mortality rates and the were the primary prey for coyotes while ro­ proportion of mortalities caused by preda­ dents, particularly kangaroo rats, were usu­ tors for adult kit foxes approached signifi­ ally the primary prey for kit foxes. Con­ cance (r ~ 0.48, d.! ~ 12, P ~ 0.09), but sumption of kangaroo rats by coyotes was mortality and predation rates for juvenile low indicating that they may not be able to foxes varied independently (r = 0.37, d.t efficiently exploit this prey. Resource par­ ~ 11, P ~ 0.23). Finally, indices of abun­ titioning between these two species also dance for both kit foxes and coyotes were was evident on the nearby Carrizo Plain positively correlated with indices of abun­ Natural Area (White et al., 1995). Similarly, dance of leporids (kit fox: r =' 0.60, dj. ~ resource partitioning was observed between 11, P ~ 0.04; coyote: r ~ 0.68, dj. ~ 10, sympatric red foxes (V. vUlpes) and coyotes P ~ 0.02). (Crossett and Elliot, 1991; Major and Sher­ burne, 1987; Theberge and Wedeles, 1989) DISCUSSION and between sympatric gray foxes (Uro~ Exploitative competition.-Coyotes and cyon cinareoargenteus) and coyotes (Cy­ kit foxes at NPRC used many of the same pher, 1993; Smith and Danner, 1990). food items indicating that exploitative com­ Greater consumption of leporids by coyotes petition may occur between these two spe­ and small rodents by kit foxes at NPRC is cies. However, overlap in resource use does consistent with observations that coyotes not necessarily indicate either the existence generally select larger items than do kit fox­ or intensity of competition (Schoener. es (Smith and Danner, 1990; White et al., 1982). Certain characteristics of foraging 1995). It also is consistent with the predic­ patterns exhibited by both species may me- tion that sympatric carnivores will partition 210 JOURNAL OF MAMMALOGY Vol. 79, No.1

prey species based on carnivore body size 1996). In the latter years of the period (Rosenzweig, 1966). 1985-1990, coyotes increased use of other The consistently high annual proportion food items, particularly anthropogenic re­ of leporids in diets of coyotes and the ap­ sources such as livestock and refuse. Also, parent non-significant relationship between use of rodents by kit foxes declined and le­ abundance of leporids and their consump­ porids became the primary prey item in tion by coyotes suggested that use was dis­ 1990. In that year, dietary diversity of kit proportionate to availability and coyotes foxes was significantly higher than that of Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 have a strong preference for leporids. Sim­ coyotes, and use of food items by the two ilar preference has been documented in oth­ species was least similar. Leporids also er locations where leporids were primary were the primary prey item used by kit fox­ prey for coyotes (Clark, 1972). Such a re­ es at NPRC in the early 1980s when abun­ lationship between coyotes and Jeporids at dance of Jeporids apparently was extremely NPRC was not unexpected because other high (Scrivner et al., 1987). Kit foxes on items identified as primary prey for coyotes the nearby Carrizo Plain Natural Area con­ elsewhere in California (Barrett, 1983; sumed primarily pocket mice (White et aI., Bowyer et aI., 1983; Ferrel et aI., 1953; 1996), but kit foxes in nearby Bakersfield Hawthorne, 1972) either were not present preyed primarily on California ground (e.g, arvicoline rodents, ungulates), or were squirrels (Cypher and Warrick, 1993). Thus, present in relatively low abundance (e.g., kit foxes in this area may be able to exploit California ground squirrels, fleshy fruits). a variety of small mammals and leporids. Use of leporids by kit faxes may be more At NPRC, heteromyid rodents are the most proportionate to availability and also may abundant small manunals (Cypher, 1995; be influenced by availability of kangaroo Otten and Holmstead, 1996) and rarely are rats. Both relative and absolute densities of important items in coyote diets (e.g., Ferrel prey influence their use (Stenseth, 1981). et al, 1953). Thus, coyotes at NPRC may Unfortunately, indices of abundance for be more limited in the prey that they are kangaroo rats were not available to deter­ able to exploit and may be leporid special­ mine if use of kangaroo rats by kit foxes ists. The more general foraging patterns of was proportionate to availability and if kit foxes compared to coyotes may reduce abundance of kangaroo rats affected use of competition and facilitate coexistence leporids. However, in a comparison of food (Pianka, 1978). Similarly, red foxes in the habits of kit foxes among five areas on Yukon exhibited greater dietary breadth NPRC in 1994. Koopman (1995) found that compared to sympatric coyotes that foraged use of kangaroo rats was disproportionate primarily on snowshoe hares (L. american­ to availability and leporids were secondary us-Theberge and Wedeles, 1989). prey items regardless of their abundance Interference competition.-Based on except where availability of kangaroo rats mortality data for kit foxes, coyotes appar­ was low. Similarly, kangaroo rats were the ently also engage in interference competi­ primary prey of kit foxes in an area adja­ tion with kit foxes at NPRC. Coyotes not cent to NPRC (Spiegel et aI., 1996). only killed kit foxes but were the primary During 1985-1990, precipitation was be­ cause of mortality for radiocollared kit fox­ low average in 1985, 1988, 1989, and 1990 es in this study. At the nearby Carrizo Plain (National Oceanic and Atmospheric Ad­ Natural Area, coyotes were the cause of ministration, 1992). This likely contributed death in 65% of mortalities of kit foxes to the decline in abundance of leporids ob­ (Ralls and White, 1995). Similarly, inter­ served from 1988 to 1990 and may have ference competition has been well docu­ contributed to low availability of rodents mented between coyotes and other species during this time (Otten and Holmstead, of fox, including red foxes (Dekker, 1989; February 1998 CYPHER AND SPENCER-COYOTE-KIT FOX COMPETITION 211

Harrison et aI., 1989; Major and Sherburne, numerical (declining abundance) and func­ 1987; Sargeant and Allen, 1989), swift fox­ tional (altered foraging patterns) responses es (V. velox-Scott-Brown et aI., 1987), to declining availability of prey. Supple­ and gray foxes (Cypher, 1993; Wooding, mentally fed kit faxes at NPRC exhibited 1984). Coyotes frequently did not consume higher survival and reproductive rates kit foxes that they killed, which also has (Warrick et aI., 1993). On the nearby Car­ been observed in other locations (Disney rizo Plain Natural Area, abundance of kit and Spiegel, 1992; Ralls and White, 1995). faxes also declined in response to drought­ Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 Thus, mortality inflicted by coyotes can not related reduction in prey availability, al­ be exclusively categorized as classic pre­ though interference competition by coyotes dation, suggesting that coyotes may engage may have been a contributing factor (White in interference competition which reduces et al., 1996). Competitive interactions prob­ exploitative competition (White et aI., ably constitute a secondary factor influenc­ 1994). ing population trends of kit foxes. If pre­ Because mortality rates of kit foxes were dation on adult kit foxes is indeed additive, correlated positively with predation rates on interference competition from coyotes may kit foxes by coyotes, mortalities of adult kit dampen population increases of kit foxes faxes attributable to predators may be at and accentuate population declines. least partially additive. Therefore, lower Coyotes occur throughout the range of abundance of coyotes might result in higher the kit fox, and kit foxes have several be­ abundance of kit foxes. Coyote control re­ havioral strategies that may facilitate co­ portedly resulted in increased abundance of existence. Partitioning of food resources is red foxes and swift foxes (Linhart and Rob­ one such strategy. Year-round use of mul­ inson, 1972; Robinson, 1961; Sargeant, tiple dens by kit foxes (Morrell, 1972) re­ 1982), and Sargeant et al. (1993) reported duces interference competition (White et an inverse relationship between abundances aI., 1995). Swift foxes also use dens to of coyotes and red foxes. The coyote-con­ avoid agonistic encounters with coyotes trol program conducted at NPRC from 1985 (Scott-Brown et al., 1987). This avoidance to 1990 did not result in greater abundance strategy is analogous to tree-climbing by of kit faxes, but this may have been due to gray faxes, which reduces interference insufficient intensity of control and low competition with coyotes (Cypher, 1993; availability of prey during the latter part of WoodIng, 1984). Finally, there is some ev­ this period (Cypher and Scrivner, 1992). idence for habitat partitioning by coyotes Predator-related mortality of juvenile kit and kit foxes (White et aI., 1995) resulting foxes may be more compensatory than that in spatial segregation that could reduce both of adult faxes. Juvenile survival may gen­ exploitative and interference competition. erally be low due to factors such as inex­ Habitat partitioning also has been reported perience, poorly developed foraging skills, between coyotes and both red foxes (The­ vulnerability during dispersal, and lower berge and Wedeles, 1989) and gray faxes social status. (Cypher, 1993; Wooding, 1984). However, Population effects.-Both exploitative it is unclear if observed partitioning is a competition and interference competition result of species-specific habitat preferences probably"" occur between coyotes and kit or exclusion of foxes from certain habitats foxes at NPRC, but indices of abundance by coyotes (Dekker, 1989). Schoener for coyotes and kit foxes generally tracked (1974) suggested that competitors could po­ each other, indicating that some factor other tentially partition life requisites along three than competition, probably food availabil­ major niche dimensions: food, habitat, and ity, is the primary factor affecting fluctua­ time. Coyotes and kit foxes may partition tions in abundance. Both species exhibited food and habitat. However, White et aI. 212 JOURNAL OF MAMMALOGY Vol. 79, No.1

(1994) did not detect any evidence of tem­ BOWYER, R. T., S. A. MCKENNA, AND M. E. SHEA. 1983. Seasonal changes in coyote food habits as de­ poral segregation between kit foxes and termined by fecal analysis. The American Midland coyotes. Naturalist, 109:266-273. Use of anthropogenic food resources BROWER, J. E., AND J. H. ZAR. 1984. Field and labo­ ratory methods for general ecology. Second ed. Wil­ (ie., livestock, refuse) by coyotes in this liam C. Brown Publishers, Dubuque. Iowa, 226 pp. study may have important implications for Cl.ARK, E W. 1972. Influence of jackrabbit density on conservation of San Joaquin kit foxes. coyote population change. The Journal of Wildlife Availability of these resources may amelio­ Management, 72:343-356. Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021 CROSSETT, R. L., II, AND C. L. El.LlOT. 1991. Winter rate prey-related declines in populations of food habits of red foxes and coyotes in central Ken­ coyote·s, thus maintaining competitive pres­ tucky. Proceedings of the Annual Conference of the sure on kit foxes at a higher level than Southeastern Association of Fish and Wildlife Agen­ cies, 45:97-103. would be experienced under natural condi­ CYPHER, B. L. 1993. Food item use by three sympatric tions. During a decline of snowshoe hare in canids in southern Illinios. Transactions of the Illi­ Alberta, coyote abundance did not decline nois State Academy of Science, 86:139-144. ---. 1995. Influence of physiography and vege­ in agricultural areas where coyotes had ac­ tation on small mammals at the Naval Petroleum cess to livestock carrion and refuse, but Reserves, California. Transactions of the Western abundance declined two to four times in Section of The Wildlife Society, 31:45-52. CYPHER, B. L., AND J. H. SCRIVNER. 1992. Coyote con­ forested areas where these alternate re­ trol to protect endangered San Joaquin kit foxes at sources were not available (Todd, 1985). the Naval Petroleum Reserves, California. Proceed­ The buffering effect of anthropogenic food ings of the Vertebrate Pest Conference, 15:42-47. sources on populations of coyotes during CYPHER, B. L., AND G. D. WARRICK. 1993. Use of human-derived food items by urban kit foxes. Trans­ ecologically stressful periods such as actions of the Western Section of the Wildlife So­ droughts could compound effects of these ciety,29:34-37. periods on populations of kit foxes. CYPHER, B. L., K. A. SPENCER, AND J. H. SCRIVNER. 1994. Food-item use by coyotes at the Naval Petro­ leum Reserves in California. The Southwestern Nat­ ACKNOWLEDGMENTS uralist, 39:91-95. This research was sponsored by the United DEKKER, D. 1989. Population fluctuations and spatial relationships among wolves, Canis lUpus, coyotes, States Department of Energy, Naval Petroleum Canis latrans, and red foxes, Vulpes vuipes, in Jas­ Reserves in California, and Chevron U.S.A., per National Park, Alberta. The Canadian Field-Nat­ Inc. under contract DE-ACOl-8SFE60S20 and uralist, 103:261-264. subcontract S-95-OOO91. Permission to trap and DISNEY, M., AND L. K. SPiEGEl.. 1992. Sources and radiocollar kit foxes was granted through United rates of San Joaquin kit fox mortality in western Kern County, California. Transactions of the West­ States Fish and Wildlife Service permit number ern -Section of the Wildlife Society, 28:73-82. PRT683011, and a Memorandum of Under­ FERREL, C. M., H. R. LEACH, AND D. R. TILl.OTSON. standing between the California Department of 1953. Food habits of the coyote in California. Cal­ Fish and Game and EG&G Energy Measure­ ifornia Fish and Game, 39:301-341. ments, Inc.lEnterprise Advisory Services, Inc. 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and Alabama. M.S. thesis, Mississippi State Univer­ ZAR, J. H. 1984. Biostatistical analysis. Prentice-Hall, sity, Mississippi State, 43 pp. Inc., Englewood Cliffs, New Jersey, 718 pp. WOODRING, W. P., P. V. ROUNDY, AND H. R. FARNS­ WORTH. 1932. Geology and oil resources of the Elk Submitted 15 September 1996. Accepted 7 March 1997. Hills, California. United States Geological Survey Bulletin, 835:1-82. Associate Editor was Edward 1. Heske. Downloaded from https://academic.oup.com/jmammal/article/79/1/204/841958 by guest on 30 September 2021