Song features and singing heights of American warblers: Maximization or optimization of distance?

Abstract

By discriminant analysis multivariate relationships were examined between quantifiable features of song and the usual rank of singing height in 19 spp. of warblers (Family Parulidae) resident in New Brunswick, Canada. A correlation of higher frequencies occurs with higher singing heights, although the lowest singing group was not different from the 2nd lowest in this respect. Associated with higher frequencies are repeated groupings of 2 phone types, low numbers of total phone types and fast frequency sweeps in the last phone of the song. Warblers with lower frequencies have more phone types per song. Warblers singing at lowest levels have large numbers of unrepeated phones or alternatively 3-5 separate phone types repeated in the series in their songs. In addition to frequency, structural characteristics of the songs are related to singing height. Results are not consistent with the view that warblers are maximizing the distance over which their songs are transmitted since low-frequency sounds are preferred on an acoustical basis at most singing heights, if not the very lowest. Warblers may be producing songs which by their frequency and structure carry mainly to individuals of biological significance to the singers, probably individuals on adjacent territories. Other explanations are considered.