Nest location within the tree and breeding parameters of Rooks Corvus frugilegus

Abstract

Capsule The position of a nest in the tree influences some parameters of reproduction. Aim To determine breeding parameters in relation to the spatial distribution of nests in trees. Methods In 2000–02 a total of 177 Rook nests were studied in seven colonies situated in eastern Poland. Breeding parameters of Rooks were compared between vertical and horizontal zones of the tree canopy. Results The vertical distribution of Rook nests in trees affected the number of hatchlings and, after eliminating a variable describing horizontal distribution, also the clutch size. The horizontal distribution of nests, their number in a vertical zone or in a tree did not affect breeding parameters. Differences in laying dates of the first eggs between vertical zones were not statistically significant. In the lowest zone (C) both mean clutch size and mean number of hatchlings were significantly lower than those in the highest vertical zone (A) and the middle zone (B). Breeding success was higher in zones A and B, while the greatest losses during incubation and feeding of nestlings were observed in zone C. However, the numbers of fledglings in the smaller proportion of nests in zone C that did produce young were similar to the numbers in nests in zones A and B. Therefore, differences between the zones in the numbers of fledglings were not significant. Conclusion Rook nests in the top zone of the tree canopy have larger clutch sizes and numbers of hatchlings at the beginning of the nesting cycle. However, in spite of the clearly lower values of these parameters and higher total losses in broods in the lowest zone, the number of fledglings was similar in all zones.