White plumage reflects individual quality in female eiders

Sexual selection predicts that males should signal their viability and health and this is often achieved with elaborate ornaments. However, females' phenotypic and genotypic quality may also be related to ornamental expression. We investigated the association between a female ornamental trait (white wing plumage) and female quality in the common eider, Somateria mollissima. Only females incubate and care for young, so male parental effort did not influence the females' condition, and the ornament is expressed only in females, so it is not a neutral correlated response to selection of the same ornament in males. We recorded the expression of this ornament in relation to the number of eggs laid and to mass loss and immunological status during incubation. Females that experienced a large mass loss and/or a reduction in immune cell levels (immunosuppression) had less white in the new wing bands produced after breeding. These results are the first to show a correlation between tolerance of reproductive costs and the expression of a strictly female ornament in a species with conventional sex roles. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.