Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Common raven (Corvus corax) populations have increased considerably in recent years in the deserts of southwestern United States. The increases are probably caused by an rise in human population densities in the desert and they may be responsible for increased raven predation on juvenile desert tortoises (Gopherus agassizii). As subsidized predators, ravens benefit from food, water, and other subsidies provided by human activities. We hypothesized that the human-provided resources are particularly important sources of food and water for ravens during summer and winter, times when natural sources of food and water are scarcer. Thus, we predicted more ravens would be found at primary sources of food and water during summer and winter than fall and spring. We tested this prediction in the west Mojave Desert by censusing ravens at six resource sites (landfill, sewage pond, golf course, towns, and two desert references) in each of three areas (Edwards Air Force Base, Mojave, and Boron). Significantly more ravens were found at landfills and sewage ponds, suggesting that these provide important resources. Although there was considerable variation among seasons and years, the prediction was partially supported. The results lend support to the suggestion that efforts to manage raven populations should focus on reducing availability of resource subsidies.