Sexual dimorphism of acoustic signals in the Common Swift

Published on 19 May 2016 in Main articles

By Konrad Ansorge

Abstract The typical screaming calls of the Common Swift Apus apus include a scream followed by a trill. The pitch and the duration of the different parts of the calls produced by breeding birds in nestboxes vary within and between individuals; these differences do not signify the bird’s sex and probably depend largely on the degree of agitation of the individual. However, the trill part of the screaming call is a reliable indicator of a bird’s sex. Female Common Swifts show an average time lapse between the trills of ≥25 ms whereas that of males is ≤20 ms. The fundamental frequency at the end of the screaming call of females is modulated by ≤40 Hz, whereas that of males is modulated by ≥50Hz.

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Common Swifts Richard Allen

Common Swifts Richard Allen