Aerial Surveys of Cliff-Nesting Raptors

In summer 1999, an extensive aerial survey of cliff-nesting raptors was conducted in the National Petroleum Reserve–Alaska (NPR–A) on Alaska’s North Slope. No similarly extensive survey had been conducted since 1977. In the interim, the regional population of the Arctic peregrine falcon (Falco peregrinus tundrius) had increased, as shown by monitoring along the Colville River. The 1999 survey assessed the present abundance and distribution of the peregrine falcon, as well as the gyrfalcon (Falco rusticolus), golden eagle (Aquila chrysaetos), and rough-legged hawk (Buteo lagopus) in most of the NPR–A. Specifically excluded from the 1999 survey were the Kogosukruk and Kikiakrorak Rivers and the Colville River below its junction with the Etivluk River. These areas had been included in other recent surveys. Peregrine falcons were found occupying 67 sites in 1999, 61 of which were in the area surveyed in 1977 and in which only four occupied sites were found. Gyrfalcons nest earlier than other raptor species in the NPR–A, and the 1999 survey was conducted too late in the season to determine occupancy of many sites. Gyrfalcons were located at only 19 sites in 1999, down from 29 in 1977, but 41 sites showing evidence of gyrfalcon use were identified, whereas only 29 such sites were identified in 1977. Eleven pairs of golden eagles were found in 1999, which is similar to the 10 pairs found in 1977. Rough-legged hawks were the most abundant and widespread cliff-nesting raptors in the NPR–A in both years. Their relative distribution was similar in the 2 years, but twice as many pairs were found in 1999 (109) as in 1977 (55). The difficulties of comparing the results of the two surveys are discussed