Copulatory and Vocal Behavior of a Pair of Whiskered Owls

feather grown in during the last molt, O = feather not molted in the last molt.readily apparent from the pronounced bleaching and wear of the vanes.The pattern of the previous molt was not sequential in four of the five (see Table 1).Irregular molting of the primaries and secondaries has been reported (Stresemann and Stresemann 1960, J. Ornithol.101: 373-403) for certain genera, including Buteo, of all Accipitridae subfamilies except Circinae, Milvinae, Perninae, and Elaninae.The Stresemanns suggested that this molt pattern evolved from the primitive pattern of molting primaries 1 through 10 in sequence in order to reduce the stress on ingrowing feathers and to minimize the loss of flight efficiency.Certain large eagles are reported to take more than a year to complete a wing molt (Spofford 1946, Auk 63: 85), but I have seen no account of this phenomenon in Buteo.Presumably these birds stop molting sometime in the fall in order that no feathers will be growing in during times of food shortage.Several factors suggest that prey is abundant year-round on this island; these include the mild climate (snow cover rarely lasts more than a few days), the fact that the entire Red-tail population (between 10 and 20 pairs) appears to be nonmigratory, the large number of migratory raptors that winter on the island, and my own snap-trapping data.I would be very interested to compare data with anyone who has similar observations of resident or wintering raptors showing incomplete molts.I thank Dean Amadon and Walter Spofford for their comments and suggestions on the manuscript.These observations were made while conducting a research project supported by the Harris