Core body temperatures of Red-tailed Hawks (Buteo jamaicensis) and Great Horned Owls (Bubo virginianus) were monitored by telemetry at intervals throughout the winter and summer. The mean body temperature of the hawks over a 24-h period was 41.1°C, compared to 39.5°C for the owls. Body temperature of both species fluctuated daily in association with periods of activity and rest. In the hawks, however, the difference between active and inactive body temperature increased in cold weather and in response to food deprivation because the birds maintained a lower nocturnal (inactive) body temperature. Hawks that were fasted in the winter kept their body temperatures 3.2°C lower at night than during the day, which may result in a substantial savings of energy for this species at night. Body temperatures of Great Horned Owls were not influenced by cold, but were lower during inactive periods in response to food deprivation. Thus, owls may also reduce metabolic expenses during periods of food shortage by physiological adjustments.