Sailors, fishermen, yachties and dolphin spotters will undoubtedly have come across this impressive seabird, which occurs in large numbers off the Portuguese coasts in summer, with smaller numbers as early as February and as late as November. In winter they move further south in the Atlantic, reaching the coasts of southern South America.
With the exception of the Gannet, Cory’s Shearwater is the largest of the common seabirds occurring in our waters. They are often found in large, loose flocks which form rafts on the sea between feeding forays. In onshore winds hundreds can be seen passing quite close inshore. Their languid, surface-hugging flight on slightly bowed wings and the almost totally white underparts distinguish them from the Great Shearwaters which sometimes occur in smaller numbers in summer and autumn, but a closely related Mediterranean form, Scopoli’s Shearwater, with the white on the underwings extending almost to the tips, can also occur in the south.
Almost the whole of the world population of Cory’s Shearwater nests in burrows on the Atlantic islands of the Azores, Madeira and Canaries, although a few hundred pairs breed on the Berlengas islands off the Portuguese coast. Their weird calls, uttered at night over the breeding grounds, have given the species the Portuguese name of ‘Cagarros’ and the islanders of Santa Maria, where I lived for a number of years, are given that nickname. So I am (almost) a ‘Cagarro’! Each year, hundreds of birds become grounded on the islands, away from the nesting slopes, and are unable to take off again. These are taken into care and released back to the sea.
Cory’s Shearwaters feed almost exclusively on smallish fish, which they catch mainly by shallow ‘plunge-diving’. Underwater photography has shown they use their long wings to very good effect below the surface in pursuit of their prey. On re-surfacing, they have to be wary of the parasitic Great Skuas which follow flocks of Cory’s and force them to disgorge their catch.
The variety of seabirds occurring off Portuguese coasts is increasing dramatically as a result of global warming and the more extreme weather events caused by it. ‘Gulf Stream migrants’ from the Caribbean were known to reach the Azores but both these and several species from the South Atlantic, including albatrosses, are now regularly reaching mainland waters.