Associations in male plumage ornamentation and reproductiveparameters in the Icelandic Black-tailed Godwit Limosa limosa islandica

摘要

Colourful breeding plumage ornamentation is widespread among birds. Males are often more ornamented than females, and such sexual dimorphism may have arisen through sexual selection, driven by female choice and male-male competition. However, in the nominate subspecies of the sexually dimorphic Black-tailed Godwit Limosa l. limosa, paler males are mated with females that invest more into reproduction, and it was suggested that a reduction of male–male competition for high quality nesting sites was one reason for this. Paler males breed in higher densities, which facilitate better group anti-predator defence and thus can increase the reproductive value of a clutch. If male–male competition for nesting sites drives sexual selection of plumage ornamentation in godwits, we expect plumage ornamentation to be positively correlated with female reproductive investment in populations experiencing strong male–male competition. We test this in the Icelandic subspecies L. 1. islandica, where a population increase has led to enhanced competition for nesting sites among males. We test whether more ornamentation in Icelandic males is related to reproductive parameters. We assessed coloration in males on the basis of photos taken of birds captured on the nest in 1993 and videos of birds at their nests in 2008. We found no relationship between male breeding plumage ornamentation and timing of egg-laying. However, more ornamented males were mated with females that laid larger eggs in both years, opposite to the pattern found in the nominate species. This suggests that male plumage ornamentation may indeed be a sexually selected signal in godwits, and that intraspecific competition may be important.