~ Diet and demographics of breeding Ferruginous and Swainson's Hawks in Texas

We collected data on the nesting ecology of Ferruginous Hawk (Buteo regalis) and Swainson’s Hawk (B. swainsoni) nests from 2003-2005 in a short-grass prairie and agricultural community in the panhandle area of northwest Texas and southwest Oklahoma, and in northeastern New Mexico (map at right, with nests used for diet sampling). We modeled 1) diet composition and provisioning rates, 2) selection of nest sites as a function of local- and landscape-level habitat, and 3) nest productivity and survival as functions of habitat, time, weather, and disturbance from installation and maintenance of video-monitoring systems.

Adult Ferruginous Hawk (photo credit Ross Tsai). Data suggest that Ferruginous Hawk demographics and habitat selection are strongly influenced by the population cycles of their primary prey, which include various species of ground squirrels, prairie dogs, and jack rabbits. Would Ferruginous Hawks still breed in our study area if their primary prey resource, Black-tailed Prairie Dogs, were extirpated? Or would a local extinction occur, like Woffinden and Murphy (1977) observed in Utah after a jack rabbit population crash?

Swainsons Hawk nestlings, which later died in the nest, possibly from insufficient rates of prey provisioning and consequent terminal dehydration. Nestlings of most altricial bird species are limited to metabolic water from food provided by adults. For species nesting in semi-arid or arid systems, water limitation could limit nestling survival (Kirkley and Gessaman 1990).