Interclutch Variation in Egg Mass among Starlings Sturnus vulgaris Reflects Female Condition

Abstract

Starlings show considerable variation in egg mass among clutches. Mean clutch egg mass was highly repeatable for females, but few characteristics of females were found to relate to egg mass. Egg mass related weakly to female age, but female age only explained a small part of the variation. Hatchling mass was strongly correlated with egg mass, but body mass at 14 d of age was unrelated to egg mass. Nestling tarsus length at the same age was related to mean egg mass in one, but not another, year. Egg mass had no effect on hatchability or fledging success, although there was some evidence that brood reduction was more severe among broods hatching from small eggs. Females that had laid larger eggs were in better condition during incubation thus suggesting that high quality females are able to lay larger eggs and to maintain higher body reserves during incubation. This was supported by the observation that females laying smaller eggs were more likely to abandon their nests during incubation.