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EFFECTS OF COYOTES ON SWIFT FOXES

coyote studies

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EFFECTS OF COYOTES ON SWIFT FOXES

Postby Coyotehunter » Thu Feb 22, 2007 11:13 am

EFFECTS OF COYOTES ON SWIFT FOXES
IN NORTHWESTERN TEXAS
Abstract
The distribution of swift foxes (Vulpes velox) in the western Great Plains has been dramatically reduced since historical times. Because coyotes (Canis latrans) have been identified as the largest cause of mortality in swift fox populations, we studied the effects of coyotes on swift foxes in northwestern Texas. We radio-collared and monitored 88 swift foxes and 29 coyotes at 2 study sites from 1998 to 2000. On site 1, coyotes had relatively high abundance (41 ± 6.8 scats/transect) and survival (0.90), whereas swift foxes had low survival (0.47), low density (0.24-0.31 foxes/km2), low recruitment (0.25 young/adult). Consequently, swift foxes had a sink population due to heavy predation from coyotes. On site 2, coyotes had low abundance (19 ± 4.9 scats/transect) and survival (0.54), whereas swift foxes had high survival (0.69), high density (0.68-0.77 foxes/km2), high recruitment (1.3 young/adult). Consequently, swift foxes had a source population due to low predation by coyotes. These initial results suggested that lower coyote numbers were beneficial to swift foxes. To test this hypothesis, we experimentally removed 227 coyotes on site 1 during the final year of the study. Subsequently, coyotes had decreased abundance (18 ± 4.5 scats/transect), whereas swift foxes had increased survival (0.63), increased density (0.68 foxes/km2), increased recruitment (1.2 young/adult), and had a source population due to lower predation by coyotes. All

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parameters remained consistent on site 2. Our results indicate that high coyote numbers can suppress swift fox populations due to heavy predation. Our findings also indicate that reductions in coyote numbers can change a sink population of swift foxes into a source population, and thus has important implications for conservation efforts of swift foxes.
Introduction
The distribution of swift foxes (Vulpes velox) in the western Great Plains has been severely reduced since historical times. Consequently, the swift fox was classified as warranted, but precluded as a threatened species by the United States Fish and Wildlife Service from 1995 to 2001. Initially, this species was decimated by several human-induced factors, including inadvertent poisoning, trapping pressure, rodent control programs, and habitat loss (Egoscue 1979, Scott-Brown et al. 1987). However, Scott-Brown et al. (1987) speculated that current populations might be suppressed due to competition with coyotes (Canis latrans). Coyotes negatively affected other fox species (Voigt and Earle 1983, O'Neal et al. 1987, Sargeant et al. 1987, Cypher and Spencer 1998), including red foxes (V. vulpes) and kit foxes (V. macrotis), thus may negatively affect swift foxes as well.
Recent research indicated the largest cause of mortality among swift foxes was predation from coyotes (Sovada et al. 1998, Kitchen et al. 1999, Olsen and Lindzey 2002), suggesting that coyotes might be suppressing swift fox populations. However, previous studies were only descriptive in nature, as no studies manipulated coyote

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numbers to determine the effects on swift foxes. This information could have important implications for conservation efforts of swift foxes. For example, coyotes might affect overall survival, density, and recruitment of swift foxes, thus limiting their recovery, or even decreasing their populations in some areas.
To investigate relationships between swift foxes and coyotes in northwestern Texas, we captured and radio-collared both species at 2 study sites from 1998 to 2001. The objectives of our study were to determine home ranges, survival, and densities of both species. We also determined recruitment rates for swift foxes. Initial data indicated that higher coyote numbers on site 1 resulted in lower swift fox survival, lower density, and lower recruitment compared to site 2. Therefore, we experimentally removed coyotes from site 1 during the final year of the study to determine if population parameters of swift foxes increased.
Study Area
Research was conducted on 2, 100-km2 study sites in northwestern Texas. Site 1 was located on Rita Blanca National Grasslands (RBNG) and adjacent private lands in west-central Dallam County (36_31'N, 102_64'W). Vegetation consisted of shortgrass prairie dominated by blue grama (Bouteloua gracilis) and buffalograss (Buchloe dactyoides) that was moderately to intensively grazed by cattle (Bos taurus). Although RBNG was open year around for hunting and trapping, during our study swift foxes were not exploited by humans, whereas coyotes were lightly exploited by hunters.

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Site 2, approximately 40 km east of site 1, was located on a private ranch surrounded by other ranches, agricultural fields, and Conservation Reserve Program (CRP) fields on the border of Dallam and Sherman counties (36_24'N, 102_19'W). Vegetation on ranches consisted shortgrass prairie dominated by blue grama and buffalograss that was moderately to intensively grazed by cattle. Agricultural fields consisted primarily of winter wheat and corn irrigated by center pivot, and grain sorghum that was not irrigated. CRP, created with the passage of the 1985 Farm Bill, retired highly erodible land from agricultural production and converted it to permanent cover. CRP fields in our study area were enrolled in 1985 and were planted to warm-season grasses, dominated by old world bluestem (Andropogon spp.) and sideoats grama (Bouteloua curtipendula). To reduce livestock losses, coyote hunting was permitted and encouraged by ranch owners on this study site, and consequently coyotes were heavily exploited. However, swift foxes were not exploited by humans.
Additional carnivores that occurred on both study sites included striped skunks (Mephitis mephitis), badgers (Taxidea taxus), and raccoons (Procyon lotor). Additional ungulates included pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus), and white-tailed deer (O. virginianus). Other mammals on the study sites included porcupines (Erithizon dorsatum), black-tailed jackrabbits (Lepus californicus), desert cottontails (Sylvilagus audobonii), black-tailed prairie dogs (Cynomys ludovicianus), Ord's kangaroo rats (Dipodomys ordii), ground squirrels (Spermophilus spp.), gophers (Geomys and Cratogeomys spp.), eastern moles (Scalopus aquaticus), shrews (Notiosorex and Cryptotis spp.), prairie voles (Microtus ochrogaster), hispid

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cotton rats (Sigmodon hispidus), northern grasshopper mice (Onychomys leucogaster), woodrats (Neotoma spp.), pocket mice (Chaetodipus and Perognathus spp.), harvest mice (Reithrodontomys spp.), and Peromyscus spp. (Lemons 2001). Predatory avian species that were summer residents included great-horned owls (Bubo virginianus), barn owls (Tyto alba), burrowing owls (Athene cunicularia), turkey vultures (Cathartes aura), Swainson's hawk (Buteo swainsoni), northern harriers (Circus cyaneus), ferruginous hawks (Buteo regalis), American kestrels (Falco sparverius), and prairie falcons (Falco mexicanus). Migratory winter species included merlins (Falco columbarius), golden eagles (Aquila chrysaetos), bald eagles (Haliaeetus leucocephalus), and rough-legged hawks (Buteo lagopus).
Methods
From August 1998 to January 2001, we captured, radio-collared, and monitored 49 swift foxes and 12 coyotes on site 1, and 39 swift foxes and 17 coyotes on site 2. Swift foxes were captured using box traps, whereas coyotes were captured using padded leg-hold traps (Kamler et al. in review). Trapping effort for swift foxes was initially concentrated near the center of both study sites and expanded outward as capture of unmarked foxes decreased. Trapping effort for coyotes was concentrated in areas where swift foxes were captured to increase the likelihood that study animals shared the same area. All study animals were ear-tagged, radio-collared, and aged by tooth wear, body size, and reproductive condition (Gier 1968, Rongstad et al. 1989). Foxes were classified

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as juveniles until the breeding season following their birth. All other foxes were considered adults. All coyotes were classified as adults because all were aged > 1year.
We recorded independent telemetry locations (White and Garrott 1990) for study animals 1-2 times per week and > 12 hours apart. We radio-tracked from vehicles using null-peak systems which consisted of dual, 4-element Yagi antennas. We conducted radio-tracking primarily during 1800-0900 hours, when swift foxes and coyotes were likely to be most active (Andelt 1985, Kitchen et al. 1999). We calculated location estimates using the maximum likelihood estimation option in the program Locate II (Pacer, Inc., Truro, Nova Scotia, Canada). Mean error for reference collars (known locations) was 84 m (95% of errors were <145>40 locations and >9 months of radio-tracking. Due to emigrations and early

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deaths, annual home ranges were calculated only for 14 swift foxes (7 male, 7 female) on the treatment site, and 13 (4 male, 9 female) on the comparison site. Home ranges were not calculated for transient coyotes because they were monitored intermittingly throughout the year and had < 30 total locations. Home range sizes for coyotes were compared only in 1999, as coyote removal efforts eliminated all radio-collared coyotes from 1 study site in 2000. On each site, preliminary analysis indicated home range sizes of swift foxes and coyotes did not differ between sexes, thus sexes were pooled and compared between sites and years. Differences between mean home range sizes were calculated using t-tests (Zar 1996), and deemed significant when P < 0.05.
Annual survival rates were determined for swift foxes and coyotes using MICROMORT (Heisey and Fuller 1985). Causes of mortality were determined by necropsy. We classified swift fox deaths as coyote predation if fox carcasses had hemorrhaging and puncture wounds consistent with that from coyote bite marks. Because a major highway occurred in the middle of only 1 study site, we censored foxes that died from vehicle collisions. For each study site, data were initially analyzed in intervals of biological seasons to meet the assumption of constant survival (Heisey and Fuller 1985). Because preliminary analyses showed that survival did not differ among seasons, data were grouped and compared between sites and years using Z-tests (Heisey and Fuller 1985, Nelson and Mech 1986). Differences in survival and cause-specific mortality rates were deemed significant when P <0> 0.60 occurred

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only after we removed coyotes on the national grasslands, and during all 3 years on site 2 where coyotes were already reduced by humans. Annual survival > 0.60 was reported only by Kitchen et al. (1999) in Colorado, and Olsen and Lindzey (2002) in Wyoming (2 of 3 years). Unfortunately, no previous studies determined recruitment rates for swift foxes. Thus, whether other populations of swift foxes were sink or source was not known. Our results suggest that recruitment rates for swift foxes should be determined in future studies, as other swift fox populations with relatively low survival also might exhibit sink populations.
The severe negative effects that coyotes have on swift foxes might be the result of previous wolf (Canis lupus) extirpations, and the effect this had on canid hierarchy. Wolves are known to suppress coyote populations, but not fox populations, as canid competition is most intense in more similarly-sized species (Peterson 1995). For example, predation and displacement of coyotes by wolves has been reported in Canada, Alaska, Yellowstone National Park (YNP), and Minnesota (Berg and Chesness 1978, Fuller and Keith 1981, Carbyn 1982, Peterson 1995, Crabtree and Sheldon 1999). Similar to coyote predation on swift foxes, wolves killed but did not consume coyotes (Carbyn 1982, Peterson 1995), suggesting that wolves killed coyotes for reasons other than food. After wolves were introduced into YNP in the mid-1990s, wolf killings of coyotes resulted in a 50% sustained reduction in the coyote density (Crabtree and Sheldon 1999). This information suggests that prior to European colonization, wolves suppressed coyote densities at approximately 50% of their carrying capacity in central North America. The historic suppression of coyotes by wolves allowed for relatively

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abundant red fox populations in the northern Great Plains (Johnson and Sargeant 1977, Peterson 1995). Similarly, in the western Great Plains, the historic occurrence of wolves apparently allowed swift fox populations to thrive, as wolves suppressed coyotes populations but not the smaller swift foxes (Johnson and Sargeant 1977, Sovada et al. 1998).
Management Implications
Coyotes can suppress swift fox populations by heavy predation, apparently due to competition or territorial behavior, as swift fox carcasses were not consumed. Consequently, human reductions in coyote numbers were beneficial to swift foxes. In human-altered areas, constant reductions in coyote numbers by hunters and local landowners resulted in a source population of swift foxes, even though natural habitat was restricted and fragmented. Thus, even fragmented and relatively small areas of natural habitat can support viable populations of swift foxes, if coyotes numbers are constantly reduced. Although habitat loss and fragmentation has severely restricted the distribution of swift foxes in the western Great Plains (Egoscue 1979), protecting remaining natural and contiguous habitats may not be adequate to maintain viable swift fox populations in the long term. In unbroken expanses of natural habitat on Rita Blanca National Grasslands, swift foxes exhibited a sink population due to high numbers of coyotes. Under these circumstances, coyote hunting should not be restricted, and, in fact, may need to be encouraged by wildlife managers. The coyote reduction program we conducted on the national grasslands was successful in changing a sink population of

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swift foxes into a source. Thus, if natural or protected areas are little hunted by humans, then local coyote reduction programs should be conducted if conservation of swift foxes is a desired management objective. However, before conducting a coyote reduction program, wildlife managers need to determine if swift foxes are below their carrying capacity, as coyote reductions may not be beneficial otherwise.
Acknowledgments
This project was funded by Texas Tech University, Texas Parks and Wildlife Department, United States Forest Service, United States Department of Agriculture's Wildlife Services program, and Section 6 Grant E-1-12 from the United States Fish and Wildlife Service's Endangered Species Program. Kansas Department of Wildlife and Parks and BWXT Pantex loaned us equipment. We thank C. C. Perchellet for assistance with the project. We also thank the many landowners in Sherman and Dallam counties that allowed us to conduct research on their land. A special thanks goes to F. Pronger, who contacted us about swift foxes, then allowed us to use his ranch as a second study site. Our research protocol was approved by the Texas Tech University Animal Care and Use Committee. This is a Texas Tech University, College of Agricultural Sciences and Natural Resources technical publication.


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Postby onecoyote » Tue Sep 25, 2007 6:10 pm

Nice artical, but I have my own openion lol. Swift fox and kit fox are look a likes if you ask me. If a coyote can catch one he'll sure eat it, but I don't think that happens as much as some would have you think. Actually for the most part kit and swift fox like hanging out in terrain coyotes don't really like much, normally flat open country with little vegatation.
California, Nevada, Arizona has tons of kit fox, don't look like the coyotes have put a dent in them in those three states.
New Mexico has both kinds of fox, kits and swifts and the place is loaded with em both. Kit and swift are almost always nocturnal. It's interesting most studies are takin during the day? That's why kits are endangered in California with a total population of about 10,000,000. :roll: :wink:
It's hard for me to say anything about Texas because it's all pvt land and I can't hunt it, but I sure know about the other four states.


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Re: EFFECTS OF COYOTES ON SWIFT FOXES

Postby Dcoy » Sun Oct 12, 2008 4:17 am

Good stuff.Thanks.


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Re: EFFECTS OF COYOTES ON SWIFT FOXES

Postby Prairie Ghost » Fri Oct 17, 2008 9:05 am

Good read
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