A Visual Study of Migrating Owls at Cape May Point, New Jersey

Abstract

We studied the autumn migration of owls at Cape May Point, New Jersey, on 25 nights (178.5 hr) between 12 October and 11 November 1982 using visual and auditory techniques. We detected and observed migrating owls using an AN/PVS-3A night vision scope and 10X binoculars aided by moonlight, sky glow from a town, and the beam from a lighthouse. Barn (Tyto alba, 72.9%), Saw-whet (Aegolius acadicus, 8.6%) and Long-eared (Asio otus, 8.1%) Owls accounted for a majority of the 210 individuals counted. A comparison of the numbers of owls counted with those banded at Cape May Point during the same time period revealed a larger number and percentage of Barn Owls counted than banded, and a larger number and percentage of Saw-whet Owls banded than counted. Approximately one third of all owls were counted during the first two hours following sunset and disproportionately more owls were counted with light (<3 m sec-1) northerly winds than with other wind conditions. Mean flight directions of these species were to the west-southwest. Most Barn Owls were observed at altitudes >10 m, which may account for their lower representation in the banding sample. Our observations show that visual and auditory techniques may be usefully employed in studying the nocturnal migration of owls, but also suggest that observational/count studies of migrating owls may be subject to biases similar to those affecting diurnal count studies of migrating hawks.