Influences of coastal habitat characteristics on the distribution of Cory's Shearwaters Calonectris diomedea in the Azores archipelago

Abstract

Behaviour of birds and radiotracking indicated that Cory's Shearwaters join rafts closest to the location of their nest site. Rafting numbers of Cory's Shearwaters per kilometre of coast were higher around Corvo than around other islands in the Azores archipelago. Densities were most closely correlated with the surface area of cliff in each coastal sector, both comparing between islands and across all coastal sectors in the archipelago. After accounting for effects of cliff area, residual densities of Cory's Shearwaters were weakly positively correlated with the presence of tern colonies in one analysis and negatively correlated with the presence of urban areas in another. However, there were no correlations with the presence of other breeding procellariiforms, which tended to occur only on small rat-free islets. In contrast to the situation in other parts of its range, in the Azores, Cory's Shearwaters appear to nest predominantly on large cliffs, which are free from human exploitation and may be relatively free from activities of cats and rats. As a result, the most important habitat for breeding Cory's Shearwaters in the Azores is inaccessible cliff on the large islands.