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SPEA is an Environmental not-for-profit organization whose mission is to support research and conservation of wild birds and their habitats, by promoting sustainable development for the benefit of future generations.
Home  > Marine birds > Cory's Shearwater
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Cory's Shearwater
Cory's Shearwater - Calonectris diomedea borealis (Cory 1881)
(Portuguese common name - Cagarra)


Breeding
This bird arrives in Portugal to breed in March, and the first young appear at the end of July. The juveniles leave the nest between September and November, to return 8 or 9 years later for their first breeding attempt (Mougin et al 2000). From November to March Cory's Shearwater live exclusively at sea.

Distribution and Population Size
Cory's Shearwater is mainly European in distribution, but with colonies on Cape Verde, Algeria and Tunisia. Three sub-species have been identified and that found in Portugal, Calonectris d. borealis, is found on the Berlingas, the archipelagos of Madeira, the Canaries and the Azores. The sub-species Calonectris d. diomedea is found in the Mediterranean, and Calonectris d. edwarsi is found on Cape Verde. On the Archipelago of Madeira, Cory's Shearwater is found on all islands, being very abundant on Desertas and Selvagens Islands. It is also found on all the islands of the Azores Archipelago.

The largest population of this species is found on the Azores where there are an estimated 188,000 pairs. However, the largest individual colony is found on the Selvagens Islands of Madeira: on Selvagem Grande alone, more than 15,000 pairs of this bird breed.

Identification
This is one of the largest marine birds on Portuguese territory and can be identified by its size, together with its rapid, gliding flight. Its brown upper parts and white lower parts distinguish it from the juvenile Northern Gannet, which is also large but an even brown colour.

Habitat
As with the other Procellariformes listed here, Cory's Shearwater nests in coastal cliffs, small islands and islets. The nest may be built in cavities in rocks, holes excavated in the soil or beneath large rocks, or even bushes.

Conservation
Threats

Historically, this bird has suffered from human predation, especially on Madeira where it probably caused the marked decline in the population seen in the early 1980's. Over the rest of its distribution the principle threats relate to the presence of rats, cats and other introduced mammals in its breeding areas. The destruction of nests caused by earth movements during construction, knocking over of young on training flights, and accidental capture by some methods of fishing, are the threats in some areas where it occurs.

Conservation Status and Legal Instruments of Protection

The conservation status of Cory's Shearwater is Vulnerable and dependent on management. It is listed in Annex I of the Birds Directive and Annex II of the Berne Convention. A significant area of its habitat is listed in Annex I of the Habitats Directive.

Current state of knowledge in Portugal
This is the best studied species in Portugal, having been the target of studies on the Continent, and also on Madeira and the Azores. There have been many studies of its breeding biology, diet, population genetics and population censuses. There have also been studies relating to its distribution at sea, using Compass Data-loggers to study the foraging areas in the Azores during breeding season, and others using PTTs to study dispersal patterns in the Selvagens Islands.

Notes
In the Selvagens Islands, according to documents from the end of the last century, as many as 30,000 juveniles were captured per year (Zino 1985). With the increase in number of boats able to make long journeys, it was necessary to introduce restrictions on this activity. So, in 1971 the Selvagens Islands Natural Reserve was created - one of the first reserves in Portugal.

Mougin, J.-L. & M.-C. Mougin 2000. L’évolution des effectifs reproducteurs des Puffins cendrés Calonectris diomedea borealis de Selvagem Grande (30o09’N, 15o52’W). Boletim do Museu Municipal do Funchal 52(301): 45-50.
Zino, P. A. 1985. A short history of the shearwater hunt on the Great Selvage and the recent developments on this island. Bocagiana 84: 1-14.





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