Chick begging strategies in relation to brood hierarchies and hatching asynchrony

Altricial offspring solicit food by begging, and their parents feed them ac cording-to begging intensity,which has been shown to be positively related to offspring need. Parent-offspring genetic conflict calls for analyses of evolutionary stability, and various theoretical models have shown that stab ility is possible in the framework of handicap theory. The models predict t hat a negative relationship exists between offspring condition and begging and that offspring in poorer condition should be fed preferentially. Howeve r, these predictions depend on two unsatisfactory assumptions. First, they assume a monotonically decelerated relation between condition and fitness ( this function is more likely to be sigmoid); second, they ignore physical c ompetition between siblings, which is known to be important. We examined th e significance of these issues by manipulating hatching asynchrony in brood s of starlings Sturnus vulgaris, thus controlling competitive asymmetries b etween nest mates. We created broods with senior (older) and junior (younge r) chicks and control broods with synchronous chicks. In field and laborato ry experiments, we found that seniors begged less than juniors and controls , whereas juniors did not differ significantly from controls. However, seni ors received more food from their parents and grew better than juniors or c ontrols (hence, they were in better condition). These results violate the p redictions of available theoretical models and, together with limitations i n the universality of their assumptions, indicate that fundamental aspects of parent-offspring communication are not yet understood.