Resumo

Cory’s shearwater (Calonectris diomedea) is a procellariiform seabird which breeds in the Mediterranean and the north-eastern subtropical Atlantic, and which is considered ‘‘Vulnerable’’ in Europe due to recent declines at some localities. In the Azores archipelago (Atlantic), the introduction of mammalian predators
by man has led to petrels being extirpated from the main islands, except for Cory’s shearwater. Currently, the Azorean population of Cory’s shearwaters represents 65% of the species’ world population. However, its dynamics remains unknown, although: (1) numbers might have declined by 43% between 1996 and
2001, (2) on the main islands, the young suffer mortality from introduced mammals, poachers, and urban lights upon fledging, and (3) at sea, the level of fishery mortality remains unknown.
To fill this gap, we conducted a 7-year demographic survey on a mammal-free islet in the Azores to determine adult survival rate using capture-mark-recapture of the breeders and to estimate fecundity. We also assessed urban mortality using the data from the rescue campaigns annually conducted in the archipelago. Urban mortality concerned about 6% of fledglings, but its importance greatly varied among islands. When rescue campaigns occur, the rate might drop below 0.5%. Overall, our simulations concerning the next 100 years do not allow excluding a decrease in Cory’s shearwater numbers in the Azores without rescue campaigns (by 87% under the least favourable scenario). Rescue campaigns should only slow down the decline unless, simultaneously, lower competition for nests compared to Vila
islet allows adults to breed almost every year on the main islands and juvenile survival exceeds a threshold value. Since adult survival rate was high (>0.93), an eventual decline of the Azorean population of Cory’s shearwaters would probably not result from fishery mortality of adults, but rather from poor fledgling productivity and perhaps also from low survival during the first year at sea.

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