SEA-BIRD MOVEMENTS 12'] 



rather calm and incapable of providing the albatrosses with the lift 

 necessary for them to glide their way through from the south. 



Many descriptions of the flight of the tube-nosed birds exist in 

 the literature, and some purport to analyse the motion of these wonder- 

 ful birds in aerodynamical terms. Most of them dwell in wonder on 

 the effortless flight of these great sea-birds but describe it as flight 

 and overlook the really obvious fact that in ordinary rough weather, 

 apart from the exercising of the control surfaces of the bird's wing 

 and tail and small shifts of its centre of gravity, no important work is 

 done by the bird at all. The oceanic travellers make use primarily 

 of the components of the wind reflected from the banked sides of the 

 waves and swells, and they spend their time making ground by alternat- 

 ing the use of this lift with excursions (by gravitational falls) into the 

 sheltered trough between the crests of the waves, out of the main 

 wind-stream. This is by no means a dead area for it contains various 

 moving air systems which are consequences of the impact of the wind- 

 stream on the irregular surface of the sea. A sea-bird can move for- 

 wards dead against the wind, as anyone who has watched a gull at 

 sea will have seen, by using a few wing-beats to gain height, and then 

 gliding on a long plane downwards. 



Wind is therefore an advantage from the flying sea-bird's point of 

 view. A sudden calm can strand certain ocean birds in mid-ocean, 

 especially if heavy-laden with food they may have to sit on the water 

 and wait for the wind to get up again. Usually they do not have to 

 wait very long. Most sea-birds can make good use of wind of any 

 force, and a hurricane in mid-Atlantic probably does little damage, 

 if any, to the sea-birds which happen to be there at the time. It is 

 only when sea-birds are caught on a lee shore with no sea-room to 

 manoeuvre that we get many casualties blown inland by storms. 



This seems to happen to auks quite often, and most particularly 

 to the little auk or dovekie. 



Beyond the rather well-marked boundary of the little auk's normal 

 winter distribution (see Fig. 19, p. 130, derived partly from the excel- 

 lent paper of Rankin and Duffey, 1948), which brings it closer to the 

 North Sea coast of Britain than most text-books allow, small numbers 

 regularly, and large numbers irregularly, penetrate. On both sea- 

 boards of the Atlantic, there are years in which noticeable 'flights' 

 of little auks take place within sight of shore or even overland, and 

 years in which 'wrecks' occur, both locally and over great stretches 

 of coast. In some years there are both flights and wrecks. The evidence 



