Colonies of birds constitute one of the most fascinating kinds of animal aggregations, and coloniality has long intrigued ecologists. Yet, the evolutionary origin and maintenance of this form of social reproduction remains unexplained. During the last decades, most research has been focused on how breeding success varies with colony size, as an integrative measure of the balance between the costs and benefits of group living. However, survival is another important component of individual fitness that has been largely neglected.
In an article in the August 2005 issue of The American Naturalist, David Serrano and colleagues used advanced capture-recapture modeling techniques to study if adult survival varied among differently sized colonies in the population of banded lesser kestrels of North-eastern Spain, where the birds breed under tiled roofs of abandoned farmhouses. Their findings show that adult survival is lower in small and medium colonies than in large ones, conceivably as a consequence of the lower incidence of predators in the largest-sized groups.
Moreover, individuals responded to this environmental pressure by showing higher probabilities of movement from small to large colonies than the opposite between consecutive years. Allee effects, i.e. increased individual performance with group size, are likely to be behind the maintenance of coloniality in this species. This study highlights the necessity of taking into account adult survival when studying the relationship between fitness and group size in colonial and other subdivided populations of animals.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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