Effects of Supplemental Food on Size and Survival of Juvenile Northern Goshawks

Abstract

In 1992 and 1993, 28 Northern Goshawk (Accipiter gentills) broods in north- central New Mexico were used in a supplemental-feeding experiment to determine if there was a causal relationship between food availability and survival of young goshawks. We randomly assigned 28 nests as treatments or controls. Every two days (from hatching (late April) until juvenile dispersal (mid-October)) we visited control nest stands and provided food at treatment nest stands. We measured morphological characteristics and attached tarsal- mounted transmitters with mortality switches to 42 nestling Northern Goshawks when they were 21 days old. In both 1992 and 1993, we relocated birds via telemetry every other day until mid-August. We located birds at least once a week from mid-August until mid-October in 1992, and until late-November 1993. There were no significant differences in nestling size. Treatment birds had a significantly higher survival rate during the nestling period in 1993, but not in 1992. Because most control nestlings died from predation, we attribute higher nestling survival to increased time spent in nest stands by adult females, whose presence probably deterred predators. Received 25 April 1995, accepted 20 August 1995.