Swaison's Hawk, montioring breeding and foraging behavior

The Swainson’s Hawk is a migratory raptor that was listed by the State as a threatened species under the California Endangered Species Act in 1983. Its population had declined in response to the loss of nesting and foraging habitat (and other factors, including impacts on the wintering grounds), precipitated by development and the conversion of land to agricultural uses considered unsuitable for the species. In response to land conversion and urban development, two conservation easements (totaling approximately 700 acres) have been established in Yolo County, California. The goals of these easements are to maintain nesting habitat along a riparian corridor, provide foraging habitat consisting of row crops and other open spaces, and protect the hawks from activities on these properties that could result in take. In lieu of a more natural grassland setting, Swainson’s hawks have adapted well to foraging within agricultural areas, but not all crops are equally attractive because of their vegetative structure, timing of harvest, and other agricultural operations. Since 2006, H. T. Harvey & Associates, with funding from the City of Woodland, has conducted a Swainson’s Hawk foraging preference study on over 6,500 acres of contiguous properties to assess the foraging values of the established conservation lands compared to other lands in this agricultural matrix. The conservation easement properties are centered in the study area and all surveyed properties are within 1 mile of a known nesting corridor (Willow Slough). Throughout the nine-year period of this study, Swainson’s Hawks have consistently exhibited foraging behavior that correlates with their well-known affinity for particular croplands, namely alfalfa, wheat, and row crops. We will present the results of this ongoing study, discuss how the dynamic foraging behavior of Swainson’s Hawks is influenced by seasonal farming operations and yearly variation in weather, and describe the value of conservation easements that enhance foraging habitat in this rapidly changing landscape.