28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

The Ecology Of A Subsidized Predator In The Mojave Desert: Common Raven

William I. Boarman¹, William B. Kristan², and William C. Webb^3
1U.S. Geological Survey, Western Ecological Research Center, 5745 Kearny Villa Rd, Suite M, San Diego, CA;
²Center for Conservation Biology, University of California, Riverside, CA; 
³College of Forest Resources, Univ. Washington, Seattle, WA

Subsidized predators are species whose populations survive and often thrive on resources (e.g., food, water, safety) provided by humans. Common ravens (Corvus corax) are an excellent example of a subsidized predator. Their populations have grown precipitously in recent years because of the proliferation of human activities in the desert. In a multi-year study at Edwards Air Force Base, California, significantly more ravens were found at landfills and sewage ponds than at other human-dominated and natural areas. Radio-tagged ravens moved among anthropogenic resource sites, sometimes over >100 km apart. Some ravens moved into undisturbed desert habitat. Raven abundance at a landfill decreased after garbage containment practices were changed, but the reduction was not apparent at other sites. Nestling and fledgling survivorship was higher in nests located near anthropogenic resources and predation risk was greater near those sites and close to occupied raven nests. Ravens prey on many native animals including juvenile desert tortoises. It is not known if raven predation is high enough to prevent tortoise recovery rangewide, but it is likely high enough in some areas to hamper success of recovery efforts. Aggressive efforts to reduce availability of garbage at landfills may help to reduce the raven populations regionally.