Note on the wintering of the Cory's shearwater Calonectris diomedea in the Mediterranean

Abstract

In the Mediterranean the breeding period of the Cory's Shearwater Calonectris d. diomedea shows an important inter-annual constancy and a high synchronism between individuals and colonies, with some annual differences not exceeding several days. Most birds, whether young or old individuals, leave their breeding grounds between mid- and late October, rapidly reaching the Atlantic Ocean via the Straits of Gibraltar from mid-October to mid-November. Unsuccessful breeders also desert the colony sites, doing so generally earlier than the successful breeders, depending on the failure stage and on individual behaviour. This migration results in birds wintering for a relatively short time off South Africa in the South Atlantic and Indian Oceans, although this has never been confirmed by recovered birds ringed in the Mediterranean. However, Cory's Shearwaters have been recorded wintering in the Mediterranean basin. The aim of this paper is to evaluate and discuss the extent of this wintering.