Nesting Behavior and Food Habits of Goshawks in the Sierra Nevada

MASTERS THESIS: An active goshawk nest was located in a dense stand of lodgepole pine near Donner Lake, Nevada County, California. Activities of the three young and parents were watched Division of labor between the adult male and female was marked. During the initial stages of the study the female remained close to the nest day and night. She left only to receive food from the male, to capture prey near the nest, to cache prey items and collect sprigs to bring to the nest. Her activity changed as the season progressed. Brooding time per day decreased and then ceased altogether; time spent near the nest decreased. After June 30, the female left the nest area to hunt. The female s sprig collecting activity, apparently a displacement behavior, reached a peak as brooding ceased. The male was responsible for capturing 85 percent of the food for the brood, but only the female fed the young... The female aggressively defended the nest area from human intruders but the male showed little concern. The transfer of prey items from male to female occurred throughout the study with evidence of aggression of her part after the food was exchanged. It is postulated that this aggression of the female toward the male is the mechanism which caused increased delivery of prey items by the male to meet the food demands of the young. Goshawks were observed to capture prey by 1. swooping from a hidden position, and 2. by searching in the grass of a small pond for hidden ducklings. Large animals appeared to be cached and periodically eaten by the male before being brought to the nest; small prey were delivered to the nest soon after capture. Nestling birds accounted for the largest part of the goshawks summer diet. Daily prey weights consumed by the nestlings in the course of the study were graphed. The peaking trend of the food consumption curve is caused by the food items contributed by the female. Factors responsible for this increased foraging activity of the female are 1. prey abundance in the nest area and 2. a behavioral change causing the female to hunt outside the nest area