Intraseasonal Costs of Reproduction in Starlings

Abstract

I examined intraseasonal reproductive trade-offs in European Starling (Sturnus vulgaris) females breeding in central New Jersey in 1984-1988. Among females experimentally forced to rear enlarged broods, one of four treatments reduced the likelihood of initiating a second clutch, but there was no clear relationship between first brood size or reproductive success and likelihood of initiating a second clutch. Females that initiated second clutches laid smaller first clutches, but reared larger first broods relative to their original clutches, than did females that did not initiate second clutches. For females rearing unmanipulated first broods, first brood reproductive effort did not affect the likelihood of initiating a second clutch. Among both experimental and control females, only those individuals that initiated first clutches relatively early laid second clutches. Neither brood size in manipulated broods nor reproductive success in control nests affected second brood reproductive success, but those females that reared broods larger than their clutches laid smaller second clutches. Clutch size in second broods declined seasonally, but was a poor predictor of the number of second brood fledglings. Since some second broods were successful and intraseasonal costs did not affect second brood success, it is unclear why only 44% of females initiated second broods. Compared to artificially synchronized broods of the same size, asynchronous hatching increased neither the probability of initiating a second clutch nor the reproductive success of second broods. Thus asynchronous hatching in first broods was not a strategy to increase reproductive success in subsequent broods.