Food habits and space use of gray foxes in relation to sympatric coyotes and bobcats

To investigate interspecific relationships between gray foxes (Urocyon cinereoargenteus) and sympatric coyotes (Canis latrans) and bobcats (Lynx rufus), we quantified occurrence of food items in carnivore scats and used relative abundances of scats on transects to assess space use. Dietary-overlap indices between the two canid species were high during summer and fall (x = 0.89) when fruits were prevalent in scats of both species, and were lower during winter and spring (x = 0.70) when fruits were less available. Foxes differed most from coyotes in their relatively less frequent ungulate consumption. Fox–bobcat dietary-overlap indices were relatively low in summer and fall (x = 0.37) and greater in winter and spring (x = 0.74). Foxes differed most from bobcats in their more frequent consumption of fruits and less frequent consumption of lagomorphs. Abundance of fox scats was positively correlated with abundance of coyote scats during both winter–spring (r = 0.52, p = 0.02) and summer–fall (r = 0.75, p < 0.001) and with abundance of bobcat scats during winter–spring (r = 0.59, p < 0.01) and summer–fall (r = 0.22, p > 0.10). Thus, despite similarities in diet, we found no evidence that gray foxes avoided these larger predators in space. Résumé : Pour décrire les interactions interspécifiques entre les Renards argentés (Urocyon cinereoargenteus) et les coyotes (Canis latrans) et lynx (Lynx rufus) sympatriques, nous avons quantifié la fréquence des aliments dans les fèces de ces carnivores et déterminé les abondances relatives des fèces pour évaluer leur utilisation de l’espace. Les indices de chevauchement de niches alimentaires entre les deux canidés sont élevés durant l’été et à l’automne (x = 0,89) lorsque les fruits prédominent dans les fèces des deux espèces et moins élevés en hiver et au printemps (x = 0,70) lorsqu’il y a moins de fruits. Les renards diffèrent des coyotes par leur consommation relativement moins fréquente d’ongulés. Les indices de chevauchement alimentaire entre les renards et les lynx sont relativement faibles en été et à l’automne (x = 0,37), mais plus élevés en hiver et au printemps (x = 0,74). Les renards diffèrent des lynx surtout par leur consommation plus fréquente de fruits et leur consommation moins fréquente de lagomorphes. L’abondance des fèces de renard est en corrélation positive avec celle des fèces de coyote, aussi bien durant la période hiver–printemps (r = 0,52, p = 0,02) que durant la période été–automne (r = 0,75, p < 0,001) et avec l’abondance des fèces de lynx au cours de la période hiver–printemps (r = 0,59, p < 0,01) et au cours de l’été–automne (r = 0,22, p > 0,10). Donc, en dépit de la ressemblance des régimes alimentaires, rien n’indique que les Renards argentés évitent ces grands prédateurs. [Traduit par la Rédaction] 1800 Neale and Sacks Introduction Gray foxes (Urocyon cinereoargenteus) co-occur with both coyotes (Canis latrans) and bobcats (Lynx rufus) over a large part of their range in North America. Consequently, gray foxes might be expected to experience negative interactions, including exploitation competition and interference, with the two larger predators, especially where dense populations occur in sympatry. The degree of overlap in food habits represents a major interspecific relation that strongly affects the potential for competition. Ecological relations between gray foxes and sympatric coyotes or bobcats have received little attention (Small 1971; Riley 1999; Fedriani et al. 2000). However, relations between other fox species and coyotes have been well studied and broadly characterized as agonistic, with coyotes dominant over red foxes (Vulpes vulpes; Major and Sherburne 1987; Sargeant and Allen 1989), swift foxes (Vulpes velox; Kitchen et al. 1999), and kit foxes (Vulpes macrotis; Ralls and White 1995). Relations between foxes and bobcats have received less attention, although one study that examined diet and space use showed no evidence of competition between red foxes and bobcats (Major and Sherburne 1987). Previously, we assessed niche relationships between sympatric high-density populations of coyotes and bobcats in the northern California foothills and observed few negative interactions despite extensive spatial overlap and similarities in use of habitats and foods (Neale and Sacks 2001). We hypothesized that gray foxes in the study area would be more negatively impacted by coyotes than were bobcats, owing to their smaller size as well as the omnivorous diet of both canids. We also investigated whether the intermediatesized bobcat might also overlap gray foxes in use of foods and (or) interfere with foxes’ use of space. To investigate these questions and better understand ecological relations between gray foxes and both coyotes and bobcats, we comCan. J. Zool. 79: 1794–1800 (2001) © 2001 NRC Canada 1794 DOI: 10.1139/cjz-79-10-1794 Received February 14, 2001. Accepted August 9, 2001. Published on the NRC Research Press Web site at http://cjz.nrc.ca on October 19, 2001. J.C.C. Neale1,2 and B.N. Sacks.3 Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, U.S.A. 1Corresponding author (e-mail: [email protected]). 2Present address: Graduate Group in Ecology, Department of Environmental Toxicology, One Shields Avenue, University of California, Davis, CA 95616, U.S.A. 3Present address: Graduate Group in Ecology, John Muir Institute of the Environment, One Shields Avenue, University of California, Davis, CA 95616, U.S.A. J:\cjz\cjz79\cjz-10\Z01-140.vp Friday, October 12, 2001 2:29:10 PM Color profile: Generic CMYK printer profile Composite Default screen