Why do migratory birds sing on their tropical wintering grounds?
Sorensen, Marjorie C
The American Naturalist
University of Chicago Press
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Sorensen, M. C., Jenni-Eiermann, S., & Spottiswoode, C. (2016). Why do migratory birds sing on their tropical wintering grounds?. The American Naturalist, E65-E76. https://doi.org/10.1086/684681
Many long-distance migratory birds sing extensively on their tropical African wintering grounds, but the function of this costly behaviour remains unknown. In this study we carry out a first empirical test of three competing hypotheses, combining a field study of great reed warblers (Acrocephalus arundinaceus) wintering in Africa with a comparative analysis across Palearctic-African migratory songbird species. We asked whether winter song (i) functions to defend non-breeding territories, (ii) functions as practice to improve complex songs for subsequent breeding, or (iii) is a non-adaptive consequence of elevated testosterone carry-over. We found support for neither the long-assumed territory defence hypothesis (great reed warblers had widely overlapping home ranges and showed no conspecific aggression), nor the testosterone carry-over hypothesis (winter singing in great reed warblers was unrelated to plasma testosterone concentration). Instead, we found strongest support for the song improvement hypothesis, since great reed warblers sang a mate attraction rather than territorial song type in Africa, and species that sing most intensely in Africa were those in which sexual selection acts most strongly on song characteristics: they had more complex songs and were more likely to be sexually monochromatic. This study underlines how sexual selection can have far-reaching effects on animal ecology throughout the annual cycle.
great reed warbler, Palearctic-African migrants, winter, non-breeding, song function
MCS was funded by the Gates Cambridge Trust and the Natural Sciences and Engineering Research Council of Canada. CNS was supported by a Royal Society Dorothy Hodgkin Fellowship, a BBSRC David Phillips Fellowship, and the DST-NRF Centre of Excellence at the Percy FitzPatrick Institute.
External DOI: https://doi.org/10.1086/684681
This record's URL: https://www.repository.cam.ac.uk/handle/1810/249312