Artificial dens for the conservation of San Joaquin kit foxes

Abstract

San Joaquin kit foxes (Vulpes macrotis mutica) are federally endangered and California threatened, primarily due to profound habitat loss. Kit foxes are obligate den users and in some locations den availability may be limited due to natural or anthropogenic factors. We conducted a study during 2001–2004 to determine whether kit foxes would use artificial dens, and if so, whether they exhibited a preference for den designs or construction materials. We tested six different den designs, four different construction materials, and two different chamber types. We constructed 34 dens in 12 locations in Bakersfield, CA. We conducted 9,271 den checks and detected kit foxes or their sign on 1,198 of those checks. Kit foxes may not have found one of the locations, but kit foxes used (i.e., entered) 29 of the 31 dens at the other 11 locations. Kit foxes did not exhibit preferential use of any designs, materials, or chamber types. Internal conditions (i.e., temperature and relative humidity) within artificial dens can provide thermoregulatory and moisture conservation benefits to foxes, although these benefits were not as strong as those provided by natural dens. At least nine other species were documented using the artificial dens, including some that might compete with kit foxes. San Joaquin kit foxes readily used artificial dens and clearly such dens can be used to mitigate den losses or to enhance habitat for kit foxes. Due to lower cost and ease of installation, we recommend installing two-entrance dens constructed of high-density polyethylene plastic with an irrigation valve box for a subterranean chamber.