Nesting Population, Nest Sites, and Prey Remains of Bald Eagles in Barkley Sound, British Columbia

Abstract

In 1988, the nesting population of bald eagles (Haliaeetus leucocephalus) in Barkley Sound, British Columbia was surveyed, and both the nesting habitat and the prey of these birds were investigated. Fifty-four occupied nesting territories were observed. Linear nest densities on forested islands in Barkley Sound averaged 0.11 nest/km of shoreline, and those along the perimeter of Vancouver Island in the Sound averaged 0.07 nests/km of shoreline. The number of eagles was similar to the number observed 15-17 years earlier by Retfalvi (1977). Of 80 prey remains found beneath nesting trees of eagles, birds constituted 41.2%, marine invertebrates 45.0S, fishes 10.0%, and mammals 3.8% of the identified items. The glaucous-winged gull (Larus glaucescens) was the most frequent prey species (28.3%) in the remains. Eagles also were observed to feed on herring spawn in March. The proportion of islands with nests was higher for large (>0.005 km2) islands than for smaller ones. Nests were found mostly in red cedar (Thuja plicata), but also in western hemlock (Tsuga heterophylla), sitka spruce (Picea sitchensis) and Douglas-fir trees (Pseudotsuga menziesii), at an average height of 30.3 + 13.3 m above ground. The distance of nests from shore averaged 37 + 21 m. The purposes of this study were a) to assess the size of the present population of bald eagles throughout Barkley Sound, British Columbia, b) to determine which islands and sites these eagles selected for nesting, c) to identify prey remains of eagles beneath nests, and d) to compare the population density, nest site seleciton and prey of the Barkley Sound population with those of eagles nesting in the Gulf Islands, British Columbia. This latter population was investigated in 1987 by Vermeer et al. (1989) using the same methods as in this study.