Patterns of song variation in a migratory population of pine warberls--behavioral implications in a changing climate.

Abstract

As our climate continues to change, the range of suitable habitats for many species will be in flux, which along with changes in many biotic and abiotic factors will bring about changes in migratory behavior. This has already been seen for many species of birds, which have begun migrating shorter distances and even halting migration entirely as necessary resources become available year-round. Behavioral differences between migratory and non-migratory populations of birds have been observed for some species, particularly in song repertoire size and sharing. As a way to predict how vocal behavior and patterns will change as a result of climate change, comparisons can be made between populations of pine warblers, a wood-warbler unique for the presence of migratory behavioral plasticity, with migratory populations in the northern United States and Canada, and non-migratory populations in the southern United States. Due to the absence of previous studies on pine warbler song behavior, the patterns and variation across populations was assessed to provide good baseline data with which to make future comparisons. In the assessment of two migratory populations of pine warblers in northern Michigan, I found birds to possess relatively small repertoires, singing an average of three songs each. These songs could be categorized as “first” and “second” category songs, with characteristics similar to other wood-warblers. However, the use of these songs differed dramatically from what was expected, as birds sang both first and second category songs throughout the day, showing quite unique behavior for a wood-warbler. In an analysis of song variation across a population, I found that neighbors were not significantly more likely to share songs than non-neighbors. In a comparison of note repetition rates with frequency ranges, I found a very tightly clumped distribution, falling quite close to a theoretical vocal performance limit. Though the small repertoire size and low levels of song sharing observed in this population agree with predictions about migratory songbirds, the use of first and second category songs as well as vocal performance show interesting differences from other wood-warblers that would benefit from further study. The observations collected in this study will help greatly in the study of behavioral differences in migratory and non-migratory populations, and could give great insight into the potentially farreaching behavioral consequences of climate change.