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Female–female cooperation in polygynous oystercatchers


Waders (Charadrii) provide biologists with an astonishing variety of mating systems to study 1. Male and female birds establish breeding units in which behaviour varies from monogamy, polygyny, polyandry, double clutching, lekking and serial monogamy to sex role reversal, and many mixed mating systems exist 1. This diversity is currently explained by the costs and benefits of males and females either cooperating or defecting during breeding attempts 2, 3. The oystercatcher (Haematopus ostralegus) is a typically monogamous species: removal experiments show that both parents are needed to raise chicks to fledgings 4,5,6. However, occasional polygyny has also been reported 7. Here we describe polygynous oystercatcher trios and the reproductive consequences of such polygyny. There is a ‘classical’ form of polygyny (two female territories within the male territory), but oystercatchers also show a remarkable variant, accompanied by female–female cooperation, female–female copulations and joint nesting.

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Figure 1: Frequency distribution of the degree of relatedness (rxy) for 1,000 randomly generated pairs of female oystercatchers on the island of Schiermonnikoog.
Figure 2: Mean proportion of brooded eggs in the nest for monogamous pairs (M, open circles; clutch sizes are connected with lines), aggressive polygynous trios with male help (AP+, open triangle) and without male help (AP−, filled triangle), cooperative polygynous trios (CP, open square; clutches of both females were combined, because they were brooded in one nest) and experimental monogamous nests containing copper eggs (filled circles).

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D.H. was supported by a grant and R.v.T. by a fellowship from the Netherlands Organization for Scientific Research. We thank B. J. Ens, L. van de Zande, M. Kersten, J. B. Hulscher, A.Brenninkmeijer, K. van Oers, I. de Groot, A. Helmhout, L. Klösters, R. Krijnen, F.-J. Voogd and N. J. Dingemanse for participating in the project; J. Koenes, J.Nijboer, W. Beukema and D. Visser for technical assistance; Natuurmonumenten for permission to work in their reserve; and R. H. Drent, B. J. Ens, J. B. Hulscher, J. Tinbergen and J. P. Kruijt for suggestions. The Animal Experiments Committee RuG gave permission for blood sampling and temporary clutch manipulations.

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Correspondence to Dik Heg.

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Heg, D., Treuren, R. Female–female cooperation in polygynous oystercatchers. Nature 391, 687–691 (1998).

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