Dawn song repertoires of tree swallows (Tachycineta bicolor)

Abstract

I describe the dawn songs of 38 male tree swallows (Tachycineta bicolor) recorded at five sites near Wolfville, Nova Scotia. Males deliver dawn song each morning during the hour before dawn, while flying elliptical paths above their nest sites. These dawn songs consist of syllables approximately 0.15 s long, delivered every 1.5 s. Each male has a recorded repertoire of one to seven discrete syllable types (average 2.6) and may repeat each syllable type an apparently random number of times before switching to the next. Most syllables could be classified on the basis of their structure into seven types, with much variation among renditions by different males of any given syllable type. Three of these syllable types were very similar to call notes that have specific uses at other times of day. Syllable types were randomly distributed among males and sites. In this species neither syllable type, the number of times each type is repeated (string length), nor the number of types a male sings (repertoire size) appears to carry particular messages or advertise male quality. Instead, syllable types may provide individual distinctiveness and variety in song sequences.