White-Tailed Kite Predation on a Fluctuating Vole Population

Abstract

White-tailed Kites (Elanus leucurus) are obligate predators of diurnal small mammals (Waian and Stendell, Calif. Fish & Game 56:188, 1970). Brown and Amadon (Eagles, Hawks and Falcons of the World, vol. 1, Hamlyn House, Feltham, 414 p. 1968) indicate that movement and nesting of kites are governed to a considerable extent by concentrations of mice, usually voles. Throughout much of the kite's range in California, the vole (Microtus californicus) is the major prey species. Hawbecker (Condor 42:106, 1940) noted a correlation between the nesting of White-Tailed Kites and vole density and suggested that a high population of voles is necessary for successful nesting of kites. This note compares annual changes in food habits of WhiteTailed Kites with measured changes in the density of California voles in fields over which the kites were hunting. At Hastings Natural History Reservation in Monterey County, California, populations of small mammals have been censused during the summers of 1969, 1970, and 1971, by means of mark and recapture techniques. The Reservation is a mosaic of grassland, oak woodland, and chaparral. Microtus predominately utilize the grassland areas. Estimated vole densities are shown in table 1. Although only one field was censused accurately, search for runways and occasional trapping in all other suitable fields within a 2-mile radius of the kite roosting site indicated vole densities similar to those of the censused field. TABLE 2. Species composition (%) of prey in kite pellets, 1969-71.