SEA-BIRD MOVEMENTS I3I 



These marked * constitute notable invasions of Britain, outstand- 

 ing compared with those of neighbouring years. The intervals 

 between them however are irregular : 7, 13, 17, 1 6, 5, 12, 17 and 20 

 years. 



The extreme limits to which the little auk can get, or can be carried 

 by weather, arc shown on Fig. 19, opposite. Strays have penetrated 

 the Mediterranean as far as Italy, Sicily and Malta, and one has 

 reputedly been seen in Egypt; and some have quite often reached the 

 Canaries and Azores. In some winters there is quite an invasion of 

 the unfrozen parts of the Baltic. 



In order to carry on a sailing life upon the ocean it is obviously 

 necessary for a sea-bird to be adapted to operate for a considerable 

 time from base, even though, in ordinary rough weather, it may be 

 able to sail very swiftly and make perhaps twenty or thirty miles an 

 hour. Some sea-birds, and particularly the tube-nosed birds, in their 

 early years before they make their first journeys to breeding cliffs, 

 spend certainly two and up to seven years at sea without visiting land 

 at all, possibly even without a sight of it. They are therefore adapted 

 to drinking salt water and many have been recorded as doing so 

 (shearwaters, petrels, auks and gulls). 



Another adaptation of the birds to this kind of life is the power to 

 go for long periods without food. It is known that the tube-nosed 

 birds (and also the puffin and gannet) can survive, certainly for a week 

 and possibly for very much longer, in this way. Indeed, in many 

 species the adults only relieve each other at the nest at intervals of 

 from four to seven days, and the young of some can be neglected in 

 the burrow or nest for about a week without any apparent ill-effects 

 or delay in the normal fledging period. 



Between the inshore, or coastal sea-bird, that spends its life within 

 sight of land, and often within sight of its breeding-place, and the 

 fully oceanic bird, there are many intermediate states. We think it 

 best, however, to adhere to the simple classification into the three 

 main types for which Wynne-Edwards (1930) is originally responsible. 

 The categories are inshore (or coastal), offshore (or marine), and 

 pelagic (or oceanic). According to Wynne-Edwards inshore species 

 include the cormorant and shag, the scoters, eiders and other sea- 

 ducks, most of the smaller species of Larus gulls and, at certain seasons, 

 all terns. These are the species which feed almost entirely within 

 sight of the shore, and we think that to them could certainly be added 

 the black guillemot, the divers in winter, and the red-footed and blue- 



