Singing activity stimulates partner reproductive investment rather than increasing paternity success in zebra finches
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Song is used as a signal in sexual selection in a wide range of taxa. In birds, males of many species continue to sing after pair formation. It has been suggested that a high song output after pair formation might serve to attract extra-pair females and to minimise their own partner’s interest in extra-pair copulations. A non-exclusive alternative function that has received only scant attention is that the amount of song might stimulate the own female’s investment into eggs in a quantitative way. We address these hypotheses in a captive population of zebra finches, Taeniopygia guttata, by relating male undirected song output (i.e. non-courtship song) to male egg siring success and female reproductive investment in two different set-ups. When allowed to breed in aviaries, males with the highest song output were no more attractive than others to females in an analysis of 4,294 extra-pair courtships involving 164 different males, and they also did not sire more offspring (both trends were against the expectation). When breeding in cages with two different partners subsequently, females produced larger eggs with more orange yolks when paired to a male with a high song output. These findings suggest that singing activity in paired zebra finch males might primarily function to stimulate the partner and not to attract extra-pair females.
KeywordsEnergetic costs Honest signalling Quality indicator Reproductive stimulation Song output Taeniopygia guttata
We thank Bart Kempenaers for providing facilities and various other support. James Dale provided helpful suggestions on a previous version of the manuscript. We thank Melanie Schneider for performing molecular and hormone work and Katrin Martin for help with video analyses. Our gratitude also goes to our animal care takers: Sonja Bauer, Edith Bodendörfer, Annemarie Grötsch, Johann Hacker, Markus Lehr, Jenny Minshull, Petra Neubauer, Frances Preiniger, Magnus Ruhdorfer and Agnes Türk. Funding was provided by the German Science Foundation (DFG) through an Emmy Noether Fellowship to W.F. (FO 340/1-2 and FO 340/1-3).
The study was approved by the animal care and ethics representative of the Max Planck Institute for Ornithology.
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