At Flathead Lake Biological Station in western Montana, Violet-green Swallows (Tachycineta thalassina) sunbathed during a restricted period and under specific meteorological conditions in an apparent attempt to rid themselves of ectoparasites. Sunbathing was done only in direct sunlight, at mean ambient temperatures ≥23.4 C and wind velocities of 14 km/h or less. The number of birds sunbathing at any given time was a function of both ambient temperature and wind velocity. Swallows basked at lower temperatures when wind velocities were low. Duration of basking likewise was a function of both ambient temperature and wind velocity. Length of basking bouts decreased as numbers of birds increased. Relative humidity did not significantly affect number of birds sunbathing or duration of bouts. Although numerous sites were available, swallows sunbathed only at one specific site, a reflective silver roof, and then only over a period of a few weeks from late June through July.
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Vol. 71 • No. 2