Date of Award:

5-1-1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

James A. Gessaman

Committee

James A. Gessaman

Committee

Keith L. Dixon

Committee

Barrie K. Gilbert

Abstract

This study examines the development of thermoregulation in nestling Red-tailed Hawks (Buteo jamaicensis) and Swainson's Hawks (Buteo swainsoni). Nestlings raised in captivity were exposed daily for 30 minutes to two sets of cold conditions (16°C and 5.5°C) and for 20 minutes to an artificial radiation load (1cal/cm2/min) plus a gradually rising ambient temperature (12 to 23°C). Body temperature changes during these tests were compared to nestling age, body weight, tarsal length, plumage depth, and the length of the seventh primary feather using stepwise multiple regression analyses. The analyses generally indicated that nestling age was the single most important variable in predicting the thermoregulatory capabilities of nestlings. Thermoregulation under cold conditions was more predictable than thermoregulation under heat stress. Nestling behavior during the tests is discussed in relation to strategies of heat conservation or heat dissipation. This study also quantified the natural parental behaviors at the nests of these two hawk species. The ontogeny of nestling thermoregulatory capabilities in the laboratory was compared with the incidence of thermally protective behaviors (i.e., brooding and shading) in the field. Adult brooding declined with nestling age among all nests and was discontinued at 16 to 20 days post hatching, suggesting a slightly overprotective behavior relative to nestling endothermic capabilities. Adult shading behavior was less consistent among nests, probably because of differences in nest exposures to direct sunlight. In some of the more exposed nests adult shading was provided intermittently until nestlings were near fledging age. Field observations and laboratory findings both indicate that nestling hawks of these two species do not overcome thermoregulatory problems associated with hyperthermia as readily as those associated with hypothermia. Thus, in nests exposed to direct sunlight, heat stress appears to threaten nestling survival for a greater portion of the nestling period than does cold stress.

Download

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .