26 SEA-BIRDS 



A Note on Non-breeders and Casual Wanderers 



Apart from these ii6 breeders, the limbo of twenty-six primary sea-birds and 

 one secondary sea-bird (the spectacled eider Somateriajischeri, which has been recorded 

 twice in Norway, though it breeds on the other side of the Polar Basin) consists of 

 casual wanderers, with three remarkable exceptions. These are all tubenoses 

 (two shearwaters and a storm-petrel) which breed in the southern hemisphere but 

 which cross the equator in large numbers to ' winter.' The most familiar of these in 

 Britain is the Tristan great shearwater Puffinus gravis^ which is rather similar, and 

 certainly closely related to the heavier North Atlantic or Cory's shearwater, P. 

 diomedea. Incidentally we suggest confusion between the two would be reduced if 

 P. diomedea were consistently called *North Atlantic shearwater' and P. gravis 'Tristan 

 great shearwater' — not just 'great shearwater.' 



The Tristan great shearwater nests only on Nightingale and Inaccessible Islands, 

 in the Tristan da Cunha group; possibly a few may survive on Tristan itself. The 

 population remains vast, though 'farmed' by the Tristan islanders, and an annual 

 penetration of the North Atlantic by off-season birds has put the species on the 

 list of regular and expected visitors to both West Atlantic and East Atlantic waters, 

 as well as some arctic waters of Greenland. The northward movement reaches the 

 North Atlantic in May, mostly on the west side at first, but odd birds appear in Irish 

 and west British waters in June and have even been seen then in the Skagerak; one of 

 us saw a few already at Rockall in mid-May (1949), and they were abundant there 

 and in moult by late June (1948). 



The Tristan great shearwater seldom comes close to land, and it is never 

 common in British waters within sight of shore; but some distance to sea off west 

 England, Ireland and the Hebrides it is always present in July and August; and 

 some elements usually penetrate northabout into the North Sea, descending to the 

 latitude of Yorkshire. The Tristan great shearwater is much more common than the 

 Northern Atlantic shearwater in our seas; indeed, the Mediterranean race of the 

 latter P. d. diomedea^ and Cory's race P. d. borealisy have each only once been taken ashore 

 in Britain, although birds which may have been of Cory's subspecies have several 

 times been seen at the entrance of the Channel. The only Scottish record is of one, 

 seen at sea close to Aberdeen on 10 September 1947, by R. N. Winnall. Normally 

 as Wynne-Edwards and Rankin and Duffey have shown, Puffinus diomedea does not get 

 much farther north in the Atlantic than 50°N., and that at about 30°W. It is much 

 more common on the North American coast than on that of Britain, although this 

 coast is much farther from its base; 'they seem to arrive on our coasts early in 

 August,' writes Bent, 'and spend the next three months with us, mainly between 

 Cape Cod and Long Island Sound.' The Tristan great shearwater also probably 

 reaches its greatest abundance on the North American coast, particularly in the 

 area of the Newfoundland Banks, where it is known as the 'hagdon'; from here 

 it extends every season along the coast of Labrador to Greenland; — it has been 

 recorded near Iceland. 



The other southern hemisphere shearwater that regularly visits North Atlantic 

 waters is Puffinus griseus, the sooty shearwater. It is much rarer than the Tristan 

 great shearwater, though it has been seen in British waters regularly enough to be 

 classed as an^autumn visitor. It breeds in New Zealand and its islands, in southern 

 South America and its islands, and the Falkland Islands (in places many miles 



