Predation on desert tortoises (Gopherus agassizii) by desert canids

Abstract

Desert tortoises (Gopherus agassizii) are a long-lived reptile vulnerable to predation by many predators, including desert kit foxes (Vulpes macrotis arsipus) and coyotes (Canis latrans). From 2009 to 2014, we assessed canid food habits at a study site in the Mojave Desert in California, USA, by collecting and analyzing desert kit fox and coyote scats. These canids primarily consumed small mammals and invertebrates. Desert tortoise remains occurred at an overall low frequency (<3%), indicating the opportunistic use by these canids of desert tortoise as a prey or scavenged food item. When we analyzed the desert tortoise remains further, there was a significant difference between predator type and desert tortoise age class. Coyotes consumed more than twice as many adult than juvenile desert tortoises, while desert kit foxes only consumed juveniles. Desert kit foxes are a small canid, thus limited to smaller prey items (i.e., juvenile desert tortoises), while coyotes are larger and can optimize a wider size range.