The time of first returns to land by Cory’s Shearwater Calonectris [diomedea] borealis on Selvagem Grande during the breeding period

The time of first returns to land within each attendance cycle by Cory’s Shearwater Calonectris [diomedea] borealis on Selvagem Grande (30°09'N, 15°52’W) is negatively correlated with the number of birds that will come to land in the evening. However, the mean time of first returns for each attendance cycle shows no significant variation from May to September. The Cory’s Shearwaters of Selvagem Grande are partly diurnal for at least part of their breeding cycle, in contrast to their conspecifics at other Mediterranean and Atlantic breeding localities. This behaviour may originate from when the size of the breeding population was very large, before its overexploitation and depredations in the 1960s and 1970s, and also linked to the lack of diurnal predators.