Foraging by Swainson's Hawks in a Vineyard-Dominated Landscape
2008
Swolgaard, Craig A. | Reeves, Kent A. | Bell, Douglas A.
We studied habitat use for foraging by Swainson's Hawks (Buteo swainsoni) within a complex agricultural crop matrix in California's Central Valley to ascertain if vineyards were used for foraging. Central Valley vineyard agriculture has increased recently, especially in areas supporting the highest regional numbers of Swainson's Hawks. There is concern that increased vineyard coverage may reduce the amount of foraging habitat available for Swainson's Hawks, because vineyards have been considered poor foraging habitat for this species, due to the height and density of the vines. In 2002 and 2003, we conducted road surveys to record observations of foraging Swainson's Hawks in relation to agricultural habitats. Using chi-square tests and 95%% CIs, we assessed habitat selection for foraging Swainson's Hawks and determined whether habitat use varied throughout the breeding season. Swainson's Hawks used 10 unique habitat types for foraging during the breeding season. Swainson's Hawks used vineyards less than expected and irrigated hay and dryland grain habitats more than expected, with some variation in habitat use as the season progressed. The variety of habitats that Swainson's Hawks used for foraging in our study area suggests that maintenance of large heterogeneous areas of agricultural habitats that include crops such as alfalfa, as well as large tracts of grazed grasslands, should be one of the priorities for conservation of this species in this region.
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