Impacts of coyotes on swift foxes in northwestern Texas

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 main cause of mortality in swift fox populations, we studied the impacts of coyotes on swift foxes in northwestern Texas, USA. We radiomarked 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/2 km) and survival (0.90), whereas swift foxes had low survival (0.47), low density (0.24-0.31 foxes/km(2)), and low recruitment (0.25 young/adult), and killings by coyotes (n = 8) were the major cause of death. On site 2, coyotes had relatively low abundance (19 +/- 4.9 scats/2 km) and survival (0.54) due to greater human persecution, whereas swift foxes had relatively high survival (0.69), high density (0.68-0.77 foxes/km2), and high recruitment (1.3 young/adult), and few (n = 2) were killed by coyotes. Our initial results suggested that swift foxes benefited from lower coyote numbers. To test this hypothesis, we removed 227 coyotes on site 1 during the final year of our study. Subsequently, coyote abundance decreased (18 +/- 4.5 scats/2 km), whereas swift foxes had increased survival (0.63), increased density (0.68 foxes/km(2)), and increased recruitment (1.2 young/adult), and few (n = 3) were killed by coyotes. All parameters remained consistent on site 2. Our results indicate that coyotes can suppress swift fox populations, and that reductions in coyote numbers can change a swift fox population from a sink to a source.