Body condition and the grouping behavior of brood-caring female common eiders (Somateria mollissima)

• Published in: Behavioral Ecology and Sociobiology
• Main Authors: Ost, M., Ydenberg, R.C., Lindstrom, K., Kilpi, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2003
• Subjects: abandonment; conflict; creching behavior; dispersal; evolution; group-size; gull predation; parental decisions; reproductive skew; wrens; Common Eider; Somateria mollissima
• Online Access: https://research.wur.nl/en/publications/body-condition-and-the-grouping-behavior-of-brood-caring-female-c; https://doi.org/10.1007/s00265-003-0641-0

Both theoretical and empirical work has shown that group size increases with increasing ecological constraints on solitary breeding. Ecological constraints refer to extrinsic factors such as availability of breeding sites, food or mates. Common eider (Somateria mollissima) females pool their broods and share brood-rearing duties, or rear broods alone. Females are often in poor condition at hatching, as incubation is accomplished without feeding, and variation in body condition is largely environmentally induced and thus unpredictable. We found that the intensity of and duration of parental care that females provide is positively correlated with their body condition at hatching. This suggests that body condition is an ecological constraint on successful solitary breeding. We further observed that group productivity in common eider broods is a decelerating function of the number of tending females. As predicted, females in poorer condition (i.e., facing stronger ecological constraints) were found in larger groups. This result is straightforward if solitary tenders can enter any group at no cost. However, if entry is group-controlled, stable groups of non-relatives are predicted not to occur when per capita reproduction declines with group size. The Nperson staying incentive model permits groups to form under these conditions, because reproduction is unevenly