ADAPTIVE SIGNIFICANCE OF EGG SIZE IN THE EUROPEAN STARLING - EXPERIMENTAL TESTS

Reproductive success in relation to egg size was studied in European S tarlings (Sturnus vulgaris) by swapping whole clutches between nests a t the start of the incubation period. Egg size did not reflect parenta l quality as no measure of reproductive success was correlated with th e foster mothers' mean egg size. There was a significant positive rela tionship between the mean size of the cross-fostered eggs and the subs equent mean size of hatchlings. The mean size of cross-fostered eggs d id not affect hatching success or nestling growth rates, and initial n estling size differences between broods with large and small eggs pers isted for <1 wk. No effect of mean egg size on mean nestling survival could be detected. Furthermore, a partial cross-fostering experiment, where nestlings were swapped between nests the day after hatching, fai led to demonstrate any lasting effect of egg size on nestling size. It is suggested that mean egg size may only influence reproductive succe ss during particularly inferior environmental conditions.