Distribution and nesting success of ferruginous hawks and Swainson's hawks on an agricultural landscape in the Great Plains

Authors: WIGGINS, DAVID - University Of Oklahoma; SCHNELL, GARY - University Of Oklahoma; Augustine, David

Submitted to: Southwestern Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2013
Publication Date: 9/15/2014
Citation: Wigins, D.A., Schnell, G.D., Augustine, D.J. 2014. Distribution and nesting success of ferruginous hawks and Swainson's hawks on an agricultural landscape in the Great Plains. Southwestern Naturalist. 59(3):356-363.

Interpretive Summary: We studied the nesting biology of two hawk species, the Swainson’s Hawk and the Ferruginous Hawk, in a landscape consisting of grasslands, shrublands, and cropland in Cimarron County, Oklahoma, in the southern Great Plains. Grasslands and shrublands in the study area consisted of lands grazed by cattle and lands enrolled on the Conservation Reserve Program. Ferruginous Hawks were rare and nested primarily in and around the Rita Blanca National Grassland (NG). Swainson’s Hawks were common and nested throughout the study area. Ferruginous Hawks nested in areas with more shrubland dominated by sand sagebrush and in areas with less cropland and Conservation Reserve Program fields. Swainson’s Hawks nested in areas that were similar to the overall landscape. The availability of shrublands with sand sagebrush may have an important influence on nesting density of Ferruginous Hawks and on the proportion of Swainson Hawk nests that successfully produce fledglings. We also found that Ferruginous Hawks typically nest on man-made platforms (nest platforms and windmills) that were most common in and around the Rita Blanca National Grasslands. The availability of such platforms may also influence their nesting distribution. Our results suggest that conversion of native grasslands to cropland has had negative consequences for Ferruginous and Swainson’s Hawks. In particular, loss of sandsage habitats on the southern High Plains may influence range declines in Ferruginous Hawks and breeding success for Swainson’s Hawks.

Technical Abstract: We studied nest site land cover associations, and reproductive success of two Buteo species of conservation concern on the southern Great Plains, USA. The study area was in Cimarron County, Oklahoma, where land use is dominated by row crop agriculture, livestock grazing, and Conservation Reserve Program grasslands. Ferruginous Hawks (B. regalis) were uncommon and nested primarily in and around the Rita Blanca National Grassland (NG). Swainson’s Hawks (B. swainsoni) were common and nested throughout the study area. Ferruginous Hawks territories contained more sandsage and less cropland and CRP than random sites, whereas Swainson’s Hawk territories mirrored the available landcover. Our results suggest that the availability of sandsage habitat is an important factor in determining nesting density (Ferruginous Hawks) and reproductive success (Swainson’s Hawks) on the Southern High Plains. Nest site availability also may have constrained the distribution of Buteos in our study area and is probably a major factor limiting Ferruginous Hawk nesting density. Ferruginous Hawks typically nest on man-made platforms (nest platforms and windmills) that were most common in and around the Rita Blanca National Grasslands. Our results suggest that conversion of native grasslands to cropland has had negative consequences for Ferruginous and Swainson’s Hawks. This relationship has been previously demonstrated in several studies of Ferruginous Hawks, but not for Swainson’s Hawks. In particular, loss of sandsage habitats on the southern High Plains may have contributed to range declines in Ferruginous Hawks and decreased breeding success for Swainson’s Hawks. Swainson’s Hawk reproductive success should be monitored in other areas of the Great Plains to obtain information on the factors affecting breeding success and regional population declines.