Assessment of abundance of San Joaquin kit foxes by spotlight surveys

Abstract

Biologists of the California Department of Fish and Game have conducted quarterly spotlight surveys of San Joaquin kit foxes, Vulpes macrotis mutica, and potential species of prey along seven 48-km routes since 1970. The annual reproductive cycle of the foxes was reflected by a seasonal cycle in the counts. Counts of foxes during surveys in June were correlated with total precipitation during the previous rainfall season, but not with concurrent counts of prey. Number of foxes seen/0.8-km interval was more highly correlated with estimated sighting distance based on physical features, such as hills and plains, than with current vegetation density or type. Mean number of foxes counted per survey per route ranged from two to 20. Counts of foxes increased over time on one route, decreased over time on another, and showed a curvilinear trend on two routes. The average number of foxes seen over all routes did not show any long-term trend. However, small samples, missing data, and lack of replication limited statistical analysis and interpretation of surveys. Statistical tests on simulated data similar to the data collected during the surveys indicated that larger samples, which could be obtained by replication, would be needed to detect changes in the population of foxes with any efficiency (statistical power). An expanded spotlight-survey program of kit foxes, with additional routes and replicated surveys, could be used to monitor population trends throughout the range of this endangered subspecies.