The Role of Despotism and Heritability in Determining Settlement Patterns in the Colonial Lesser Kestrel

Abstract

Avian colony size variation is an evolutionary puzzle in terms of unequal fitness payoffs. We used a long-term marked lesser kestrel (Falco naumanni) population, where individual fitness increases with colony size, to test whether subordinates are evicted despotically from the largest colonies. Yearlings were smaller and lighter, were more attacked than expected, and lost most disputes over nest holes with older birds. Agonistic interactions increased with colony size; consequently, most first breeders recruited in colonies smaller than those at which they first tried to settle. As expected when subordination is a transient state, birds dispersed to a larger colony as they got older even after breeding successfully. The population consequences of these behavioral processes were that the relative frequency of yearlings and first breeders decreased with colony size. At the same time, breeding colony size was repeatable within individuals, so we estimated the amount of heritable variation in this trait. Estimates of heritability derived from parent-offspring and full-sib analyses were consistently high (h2=0.53) when individuals reached asymptotic morphological values and presumably overcame subordinate transient states. Age-related dominance asymmetries masked resemblance among relatives in colony size, but both phenomena seem to coexist in this population and explain a considerable proportion of colony size variation.