Avond- en ochtendvluchten van Kuhls Pijlstormvogels Calonectris diomedea borealis bij ZW Tenerife (Canarische Eilanden), begin mei 1991

A combination of systematic seawatches (during 39 quarters of an hour), loose coastal observations and some counts at sea off SW Tenerife (Canary Islands; figure 1) at the end of April and the beginning of May 1991 suggests that most flying activities of Cory’s Shearwaters take place in the early morning and, even more, in the late afternoon and evening (figure 2). During the day the birds are mostly seen fishing often among pods of Bottle-nosed Dolphins, off Los Cristianos, or swimming in dense flocks. The over 30,000 pairs breeding population of the Canary Islands does not start breeding until the end of May or, more often, the beaming of June. Nonetheless, the fact that on both Tenerife and the neighbouring isle of La Gomera the main Cory’s Shearwater colonies are found N of the apparently rich fishing grounds off Los Cristianos (the only place where important numbers of dolphins were seen) indicates that many birds are already attracted to the breeding sites at this time of the year. Thus, they abandon their feeding grounds at the end of the day to move towards the colonies. This behaviour could possibly be explained by the assumption that early settling in the colonies might pay off in terms of breeding success.