Using GIS to inform managers of spatial and temporal patterns of raven predation on juvenile desert tortoise in the Mojave Desert

Common ravens (Corvus corax) have historically been a part of the ecology of the Mojave Desert. Over the past 30 years, however, their populations have increased an estimated 800-1500% due to anthropogenic influences. Ravens are known predators of juvenile desert tortoises (Gopherus agassizii). As such, ravens lower recruitment and contribute to the decline of the desert tortoise, a species listed as threatened under the Endangered Species Act. Using a historical predaceous bird nest data base (1991 - 2004) and intensive field work conducted from 2004-2007, specific nest sites in the desert that have the highest juvenile desert tortoise predation rates were identified. Predation “hotspots” were defined as areas with the highest predation rates over time. Using GIS, the spatial patterns of raven nests with evidence of predation and their proximity to 1) critical desert tortoise habitat and 2) human-provided resources were illustrated. These spatial and temporal patterns can be seen and interpreted by the “Raven Management Team,” a taskforce designated to write an Environmental Assessment for controlling raven predation of juvenile desert tortoises. In this way field research and GIS were combined to provide spatially explicit information on where to focus raven management efforts in the vast Mojave Desert.