NEST-DEFENSE BEHAVIOR OF RED-TAILED HAWKS

From 1983 to 1986 I visited 26 Red-tailed Hawk (Buteo jamaicensis) nests in east-central and southeastern Colorado. I estimated the closest distance that each defending adult approached, and recorded the number of calls that each bird gave and the number of times it dived while I was at the base of the nest tree for a 10-min period and subsequently at the nest for a 5-min period. The age and number of young in the nest, the height of the nest above the ground, and whether one or both adults were present were used as potential predictors of the intensity of nest-defense behavior. Nestling age was a significant predictor of call rate of the closest adult and nest height was a significant predictor of call rate of the farthest adult while I was at the base of the nest tree. Dive rate and closest approach were not significantly related to any measured variable. No independent variable was significantly related to nest-defense intensity while I was at the nest, however, dive rate increased and closest approach decreased when I was at the nest compared to when I was on the ground. These observations are only in part consistent with current theoretical models that predict patterns of nest-defense intensity in altricial birds.