Sibling competition in the broods of Little Egrets Egretta garzetta in a southern Tunisian breeding colony

Abstract

Asynchronous hatching is a common hatching pattern in the Little Egret Egretta garzetta, however, its role in maintaining dominance relationships and feeding hierarchy among siblings remains poorly studied. In this study, we investigated this issue using data on feeding and aggressive behaviours of Little Egrets nestlings in a southern Tunisian breeding colony. We found that senior nestlings were the first to access the food brought by their parents, and they ingested more food than their younger siblings did. Intermediate nestlings engaged the most frequently in aggression. The youngest nestlings showed a more resigned and less aggressive behaviour, therefore receiving a little less food, but much fewer pecks and injuries than their elders do. These findings stress the importance of hatching order in establishing a feeding hierarchy among Little Egret siblings. Moreover, they suggest that access to food may not be the unique factor that shapes nestlings’ feeding behaviour and competitiveness, as the avoidance of injuries caused by siblings’ attacks may be important. Finally, adult birds appeared to adopt a ‘laissez faire’ strategy, showing no feeding favouritism to counteract or reinforce the effects of hatching asynchrony on their offspring.