Nest Placement and Productivity of Ferruginous Hawks in Western Kansas

Abstract

The nesting ecology of Ferruginous Hawks (Buteo regalis) in western Kansas was studied from 1979 through 1987. During this time 100 nesting areas and 181 different active nest sites were located. Nesting density in the study area was 316.5 km2/pair and was highest (71.5 km2/pair) along the Smoky Hill River, where chalk outcrops were common. On average, 38 nests and 43 percent of nest areas surveyed annually from 1979 were active each year. Nests were large (up to 190 cm wide and 180 cm deep), but averaged 100130 cm across and 30-50 cm deep. Nests were typically composed of old fruit stalks and stems of Yucca as well as bits of Russian thistle (Salsola kali), cow chips, and occasional wire. The majority (71.8%) of active sites were on ledges; butte, tree and ground nest sites were less common. Compass orientation of ledge nests tended to be northwest, but was statistically random. The majority (76.4%) of nesting areas included white or yellow chalk outcrops surrounded by rangeland. Only one nesting area included less than 25 percent rangeland and more than 75 percent cropland. Half of all active sites were considered impossible for quadrupedal predators to access and only 29.2 percent were easily accessed from one or more directions. Most (81.9%) nesting areas were within 8 km of active black-tailed prairie dog (Cynomys ludovicianus) towns, but 86.9 percent of areas were not adjacent to dog towns. Hawks may avoid nesting in cropland sites, ground sites, and easily-accessed sites, suggesting that sites with low levels of human and predator disturbance may be favored. Productivity varied greatly among sites, but was significantly higher at inaccessible sites. Accessible sites within eye-view of prairie dog towns were the least productive, perhaps because unsuccessful predators of prairie dogs turn to hawk eggs and nestlings as alternative prey. Variable nest placement, so typical of this species, may occur because undisturbed sites are actively selected and undisturbed sites have variable characteristics throughout the species' range. This content downloaded from 207.46.13.94 on Mon, 05 Jun 2017 18:26:41 UTC All use subject to http://about.jstor.org/terms VOLUME 92, NUMBERS 3-4 133 The Ferruginous Hawk (Buteo regalis) is a conspicuous inhabitant of semiarid grasslands and sparse woodlands of the western United States and prairie provinces of southern Canada. Formerly one of the most abundant hawks in these regions its populations have declined, primarily because of increased human domination of the land (Bechard, 1981; Houston and Bechard, 1984; Schmutz, 1984). In order to determine the abundance and productivity of Ferruginous Hawks in Kansas (the eastern border of the species' range) this species was monitored beginning in 1978. The objective of this paper is to document utilization of habitat and productivity during the breeding seasons of 1979 through 1987. Nests are described, nest site characteristics quantified and nest placement related to reproductive success.