The influence of colony characteristics on some breeding parameters in the Cory´s Shearwater Calonectris diomedea borealis

Full article

Published:

Volume 46(1), June 1999. Pages 45-51.

Language:

English

Keywords:

breeding parameters, Calonectris diomedea, colony quality, Cory’s Shearwater, Selvagem Grande.

Abstract:

The influence of colony characteristics on some breeding parameters has been studied during the past ten years in two adjacent colonies of Cory´s Shearwaters Calonectris diomedea borealis in Selvagem Grande (30º09´N, 15º52´W), where the behaviour of the birds was strikingly different, the nervousness of the birds of the first one contrasting sharply with the quietness of those of the second. We have analysed whether these behavioural differences were associated with differences in the origin of the birds, their size, their breeding success, their breeding experience, their breeding frequency or their faithfulness to mate and nest site. Some of these parameters have shown significant differences. The new breeders in both colonies did not differ either in their origin, their age or their size. On the other hand, the birds of a colony were on avera-ge less experienced than those of the other, less faithful to their nest-site, less successful in breeding and they presented a lower rate of return to their colony, if not a lower survival rate. These differences, obviously colony-dependent, probably resulted from differences in breeding sites -all the birds breed in deep cavities in one of the colonies and only one third of them in the other- and climatic factors (exposure to the prevailing winds). Whether they died or they moved, the breeders did not stay in an unfavourable colony as long as they did in a favourable one. Consequently, highly experienced birds were rare and the average experience, the breeding success and the faithfulness to the site were low on average in the unfavourable colony.