PROBLEMS WITH MANAGEMENT OF A NATIVE PREDATOR ON A THREATENED SPECIES: RAVEN PREDATION ON DESERT TORTOISES

Common ravens (Corvus corax) are a major predator on the threatened desert tortoise (Gopherus [=Xerobates] agassizii). Large numbers of juvenile tortoise shells have been found beneath known raven nests and perches; many shells that show evidence consistent with raven predation have been found sporadically throughout the range of the tortoise; significant proportional decreases in juvenile size/age class distributions have been identified; and people have observed ravens killing, carrying, and consuming juveniles. In 1988 the U. S. Bureau of Land Management initiated a process to evaluate, design, and implement a program to reduce raven predation on desert tortoises. A pilot program was temporarily halted by a law suit filed by the Humane Society of the United States, and a draft long-term plan and Draft Environmental Impact Statement were subsequently issued and are now being modified. Several complex issues have arisen in attempting to design and implement control of ravens including: pitting one native species against another, making management decisions in light of data of varying scientific validity and depth, targeting individuals versus populations, and managing a predation problem over a broad geographic range. Addressing each of the concerns is highly problematic and the solutions are not always satisfying