Spatio-temporal structure and reproductive success in a rook (Corvus frugilegus) colony

Abstract

We have studied how individual decisions about timing of breeding and nest location affected the reproductive success of rooks by tracing the formation of a rook breeding colony in Hortobagy NP (Hungary), during the breeding season in 1999.\n\nWe have found that birds who built nests earlier also laid eggs earlier and had larger clutch size but had no had more offspring than late nesters. Distance of the nest from the centre or edge of the colony did not affect the reproductive success though rooks generally settled closer to the centre and further from the edge than it can be expected by assuming random distribution. The colony showed high breeding synchrony since date of egg laying varied less than date of nesting but synchrony did not influence the breeding success. Hatchlings survival rate and number of offspring increased with local nest density and rooks clustered their nests more than it can be expected by random settlement. Nest sites of early and late nesters did not differ regarding the distance from the centre or the edge of the colony but late nesters chose nest sites in more densely populated regions.\n\nThe results indicate that individuals may follow different strategies to increase their reproductive success. It is prospectively advantageous to build the nest and lay eggs earlier, in turn, its worth nesting in already more densely nested areas for late beginners. We suggest that a game theoretical approach may be useful if we try to understand the adaptive significance of colonial breeding.