Mate fidelity in Cory's Shearwater Calonectris diomedea on Selvagem Grande

In the Gory's Shearwater Calonectris diomedea borealis breeding on Selvagem Grande (30 degrees 09'N, 15 degrees 52'W), mate fidelity averaged 71.4%. T wo-thirds of the changes were the result of the absence of the former mate and one-third only, carried out in its presence, were true divorces. The ra te of divorce and the rate of replacement of an absent former mate had incr eased since the beginning of the 1980s. Among young and inexperienced birds , the rate of divorce decreased with the increase of age and experience bef ore becoming stable. Breeding failure during the previous year increased th e probability of divorce. Temporary non-breeding increased both the rate of divorce and the rate of replacement of an absent former mate.