Fighting to stay: the role of sibling rivalry for delayed dispersal

In many bird species with delayed dispersal, siblings differ in how long they postpone independence. Some offspring remain with their parents for a year or more and generally forego personal reproduction, while other siblings disperse in the first summer of life. We studied the basis for this variation by following dispersal among newly fledged Siberian jays, Perisoreus infaustus, carrying radiotransmitters. Postponed dispersal was the preferred option. Sibling rivalry preceded dispersal, and the larger and socially dominant siblings within broods were more likely to stay. No sex effect was found: males and females were just as likely to delay dispersal. This role of sibling rivalry shows that models explaining delayed dispersal based on ecological constraints outside the natal territory are too simplistic. The process of within-brood competition in determining which individuals disperse and which ones delay dispersal indicates that there are benefits to be gained from remaining in the natal territory. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.