Habitat-dependent song divergence in the little greenbul: an analysis of environmental selection pressures on acoustic signals.

Hans Slabbekoorn — 2008-05-09T14:37:41-00:00

Evolution; international journal of organic evolution, Vol. 56, No. 9. (September 2002), pp. 1849-1858.

Bird song is a sexual trait important in mate choice and known to be shaped by environmental selection. Here we investigate the ecological factors shaping song variation across a rainforest gradient in central Africa. We show that the little greenbul (Andropadus virens), previously shown to vary morphologically across the gradient in fitness-related characters, also varies with respect to song characteristics. Acoustic features, including minimum and maximum frequency, and delivery rate of song notes showed significant differences between habitats. In contrast, we found dialectal variation independent of habitat in population-typical songtype sequences. This pattern is consistent with ongoing gene flow across habitats and in line with the view that song variation in the order in which songtypes are produced is not dependent on habitat characteristics in the same way physical song characteristics are. Sound transmission characteristics of the two habitats did not vary significantly, but analyses of ambient noise spectra revealed dramatic and consistent habitat-dependent differences. Matching between low ambient noise levels for low frequencies in the rainforest and lower minimal frequencies in greenbul songs in this habitat suggests that part of the song divergence may be driven by habitat-dependent ambient noise patterns. These results suggest that habitat-dependent selection may act simultaneously on traits of ecological importance and those important in prezygotic isolation, leading to an association between morphological and acoustic divergence. Such an association may promote assortative mating and may be a mechanism driving reproductive divergence across ecological gradients.

Cities Change the Songs of Birds

Hans Slabbekoorn — 2008-05-09T14:15:57-00:00

Current Biology, Vol. 16, No. 23. (5 December 2006), pp. 2326-2331.

Summary Worldwide urbanization and the ongoing rise of urban noise levels form a major threat to living conditions in and around cities 1, 2, 3 and 4. Urban environments typically homogenize animal communities, and this results, for example, in the same few bird species' being found everywhere 5 and 6. Insight into the behavioral strategies of the urban survivors may explain the sensitivity of other species to urban selection pressures. Here, we show that songs that are important to mate attraction and territory defense have significantly diverged in great tits (Parus major), a very successful urban species. Urban songs were shorter and sung faster than songs in forests, and often concerned atypical song types. Furthermore, we found consistently higher minimum frequencies in ten out of ten city-forest comparisons from London to Prague and from Amsterdam to Paris. Anthropogenic noise is most likely a dominant factor driving these dramatic changes 7, 8 and 9. These data provide the most consistent evidence supporting the acoustic-adaptation hypothesis since it was postulated in the early seventies 10, 11 and 12. At the same time, they reveal a behavioral plasticity that may be key to urban success and the lack of which may explain detrimental effects on bird communities that live in noisy urbanized areas or along highways.

CiteULike: di lusvecica Slabbekoorn

Habitat-dependent song divergence in the little greenbul: an analysis of environmental selection pressures on acoustic signals.

Cities Change the Songs of Birds