The Singing Behaviour of Yellow Warblers

Abstract

Yellow warblers (Dendroica petechia aestiva), like other wood-warblers (Parulinae), use different songs in different circumstances. Analysis of recordings of 28,697 songs from 17 wild male yellow warblers from 1983 to 1988 at Amherst, Massachusetts, U.S.A., showed a consistent pattern of singing behaviour. I found that each male yellow warbler has a repertoire of songs divided into a single Type I song and a group of Type II songs. The patterns of song use are standardized, but the song types used as Type I and Type II songs are not; some males' Type I songs were similar to others males' Type II songs. Type I songs are sung relatively slowly in long runs of the song during daylight, are used near females, and, as demonstrated by mate removal experiments, are used more by unmated than by mated males. Type II songs are used in a dawn song bout, are sung relatively rapidly with much switching among song types, and are used in interactions with other males. Type I songs seem to have higher frequencies of modal intensity, especially in the initial phrase, and to have a greater increase in amplitude at the start of the song than do Type II songs. There may be some minor variation in the ways individual males use Type I and Type II songs, but the overall pattern of use is similar among males. Types I and II songs seem to be male-female and male-male signals, respectively. Thus, female response to song may have selected for a relatively simple signal with a high frequency of modal intensity, while male response to song may have selected for a relatively complex, low frequency signal.