Alternative mating strategies in Eurasian Reed Warblers: extra-pair paternity and egg dumping

Abstract

Alternative mating strategies, involving mating outside a social pair bond, have been studied intensively during the last few decades. However, we are still far from understanding what factors affect their frequencies in wild bird populations. In 2006–2011 we studied Eurasian Reed Warblers breeding in the nature reserve “Stawy Milickie” in SW Poland, and analysed the frequency of extra-pair paternity (EPP) and intra-specific brood parasitism (IBP). We genotyped a total of 786 nestlings from 259 nests. EPP offspring constituted 13.40% of all young (from 7.63% to 22.82% in different study years), and they were found in 21.62% of the broods (from 14.6% to 32.7% annually). The mean proportion of females with EPP young was 24.2% (from 16.2 to 41.7% annually). The proportion of EPP young in nests containing any EPP offspring ranged from 25% to 100% (on average 60%) and was not related to brood size. EPP young in one nest were sired usually by one or two males (92% of all cases), but we recorded one brood with three EPP fathers and one brood of four, where each young was sired by a different EPP male, and none by a social male. We found only one case of intra-specific brood parasitism (IBP). The brood with IBP constituted 0.39% of all examined broods, while the nestling that hatched from the dumped egg constituted 0.13% of all young whose parents were genotyped. We conclude that extra-pair paternity is a relatively common and regularly occurring alternative mating strategy in our study population of Reed Warblers, while intra-specific brood parasitism is extremely rare.

Keywords:

• Extra-pair paternity
• egg dumping
• intra-specific brood parasitism
• Eurasian Reed Warbler
• Acrocephalus scirpaceus

Acknowledgments

We are grateful to Giulia Casasole, Monika Czuchra, Alicja Dziachan, Maria Podżorska, Stanisław Rusiecki, Magdalena Soboń, and Łukasz Tomasik for field assistance. In 2006-07 the research was financially supported by the Polish State Committee for Scientific Research [grant 2P04F05330] and Max Planck Institute for Ornithology, and in 2006–2013 by the University of Wroclaw. Molecular analyses were finansed by Polish Ministry for Science and Higher Education [grant NN 304 390939 for HS].

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Polish State Committee for Scientific Research [2P04F05330]; Polish Ministry for Science and Higher Education [NN 304 390939].