Finding a Fox: An Evaluation of Survey Methods to Estimate Abundance of a Small Desert Carnivore (Extract)

Populations of large and small carnivores are threatened or imperiled throughout the world[1]. With increasing human populations and subsequent habitat loss and fragmentation, declines in natural prey, increased human persecution and illegal poaching, many carnivore species have declined in number and now occupy a fragment of their former range. Paramount to species management and conservation is knowledge about the status and distribution of many carnivore species. A question often facing wildlife agencies and conservation groups is how many animals are there and what is the population trend? However, many carnivore species are difficult to survey due to their low densities, are generally nocturnal and elusive, and wary of humans[2]–[6].

Kit foxes (Vulpes macrotis) are a slim, small canid (1–3 kg body mass) with ears that are relatively larger than those of other North American canids, are considered to be monestrus and socially monogamous, and are a dietary generalist feeding on rodents, insects, lagomorphs, ground-nesting birds, and reptiles[7]. Historically, kit foxes were once abundant and distributed throughout the desert and semi-arid regions of southwestern North America, ranging from Idaho to central Mexico[7]. Their range-wide decline has warranted the kit fox to be state-listed as endangered in Colorado, threatened in California and Oregon, and designated as a state sensitive species in Idaho and Utah[8]. However, a comprehensive study of kit fox abundance across its range is lacking, with the majority of studies focused on the endangered subspecies, the San Joaquin kit fox (V. macrotis mutica). In Utah, where kit foxes were once considered the most abundant carnivore in the west desert[9],[10], the kit fox has been in steep decline over the past decade[2],[11],[12].

Current methods used for surveying kit foxes and their close relative the swift fox (V. velox), include capture-recapture[2],[13]–[17], spotlight surveys[2],[13]–[15],[18], scent station surveys[2],[13]–[15], scat deposition transects with and without scat detection dogs[2],[14],[15],[17],[19], track counts[14], activity index[15], and howling response[14]. Generally these methods have been evaluated in study areas with a relatively high fox density. How well these methods will perform for monitoring fox abundance in a low-density, widely dispersed kit fox population is unknown. We tested 4 survey methods (scat deposition, scent station, spotlight, trapping) on the U.S. Army Dugway Proving Ground (DPG), Utah, with the primary objectives to (1) determine detection probabilities for each method, and (2) evaluate how well the indices of relative abundance for each survey method correlate with known kit fox abundance as determined from available radio-collared animals. The kit fox population in the west desert of Utah is considered low density, declining in abundance, and widely dispersed[11],[20],[21].