The Attack and Strike of Some North American Raptors

George E. Goslow,
1971 The AUK: A Quarterly Journal of Ornithology  
QUALITATIVE observations of the attack and strike of raptorial birds are numerous, but few quantitative measurements are available of the velocity, descent, acceleration, and deceleration of the pelvis, legs, and feet. My anatomical studies of the adaptations of the pelvic limb of selected species of North American birds of prey (MS) led to the present study because an understanding of how raptors use their feet and legs during the attack and strike facilitates the interpretation of anatomical
more » ... tion of anatomical differences. I used cinematography as a means of recording these data accurately (Hildebrand, 1963(Hildebrand, , 1964. The data presented here are somewhat limited. As the prey species were loosely tethered to the ground or a piece of canvas some distance from the raptor, the prey situations presented to the predator were not so varied nor were the prey so active as those normally encountered. Secondly although some variety of prey species was used, it was not possible to present each hawk or falcon with many different kinds. A given species of raptor captures a diversity of prey: Beebe ( 1960) and Storer (1966) indicate that the accipters and falcons are opportunists, preying upon those animals available and most easily secured. Possibly hawks and falcons attack and strike larger prey in a different manner than they do smaller ones. Lastly, an individual bird may employ a variety of hunting, attacking, and striking attitudes not characteristic for its particular species (Cade, 1960; White, 1962; Mead, 1963). MATERIALS AND METHODS I photographed the attack and strike of six species of raptors. The falcons and hawks studied had been trained for falconry. I used a Traid Photo-Sonics 16-1B electric camera at film speeds from 800 to 1000 fps and exposures from 1/3000th to 1/5000th of a second. Precise determinations of film speed were made possible by a timing light that marked the margin of the film at intervals of one millisecond. The hawks and large falcons were filmed at a distance of 30 feet using a Navitar 90 mm f/1.9 lens. Sparrow Haxvks (Falco sparverius) were filmed with a 15 mm f/2.3 lens at a distance of 42 inches. With the exception of Prairie Falcons (F. mexicanus) and Peregrine Falcons (F. peregrinus), the birds were filmed against a background 6 feet high and 13 feet long on which was ruled a grid of 10-cm squares. To facilitate measurements for the smaller species (F. sparverius), the grid was altered to 5 cm wide by 10 cm high. The circumstances at the time of the recorded strike were similar for the accipiters and Red-tailed Hawks (Buteo jamaicensis). The prey was tethered loosely 3 feet in front of the grid. The camera was mounted at right angles to the grid and the hawk 815 The Auk, 88: 815-827. October 1971
doi:10.2307/4083840 fatcat:633mgtzawzbrxmb27bqbh3epvi