LIFE HISTORIES OF NORTH AMERICAN GULLS AND TERNS. 71 



murres and cormorants off their nests for several houre without 

 any apparent damage from the gulls. 



Behavior. — The flight of the glaucous-winged gull is buoyant, 

 graceful, and pleasing, and its plumage is always spotlessly clean 

 and neat. A gull in flight is one of nature's most beautiful creatures 

 and one of its triumphs in the mastery of the air. It was a never- 

 ending source of delight to watch these graceful birds following the 

 ship at full speed without the slightest effort, dropping astern to 

 pick up some fallen morsel or forging ahead at will, as if merely 

 playing with their powers of flight. Sometimes the same individual 

 could be recognized day after day by some peculiarity of marking. 

 They seem thoroughly at ease on the wing. Several times I saw one 

 scratch its head with its foot, as it sailed along on set wings, without 

 slackening its pace at all. When traveling against a strong head 

 wind I have seen one sail along for miles without moving its wings, 

 except to adjust slightly the angle at which they were held, keeping 

 alongside the ship, forging ahead, or dropping astern, as it wished, 

 and rising or falling to suit its fancy. When left far astern to pick 

 up food off the water it would give a few flaps when rising, set its 

 wings, and soon catch up with the ship. This power to sail almost 

 directly into the teeth of a strong wind has caused much discussion, 

 as it has been noted in the herring gull and other species. Various 

 theories have been advanced to account for it, all of which are more 

 or less unsatisfactory. To my mind it is simple enough to under- 

 stand if we can realize that a gull is a highly specialized, almost 

 perfect sailing vessel, endowed with instinctive skill in navigating 

 the air to use the forces at its command to advantage. With a clear 

 knowledge of the forces at work when a ship sails, close hauled, 

 to within a few points of the wind, we can imagine the gull sailing 

 along a vertical plane, in which the force of gravity replaces the 

 resistance of the water against the keel and the wind acts against 

 the gull's wings as it does on the sails of the ship; the resultant of 

 these two forces is a forward movement, which the gull controls by 

 adjusting its center of gravity and the angle of its wings. 



It is evident from the foregoing accounts that the glaucous- 

 winged gull is decidedly a sociable species on its breeding grounds 

 where it seems to nest in perfect harmony with its neighbors in 

 close quarters. It also associates on migrations and during the winter 

 with various other species of gulls, with all of which it seems to 

 be on good terms. The adults can readily be distinguished from 

 the white-winged species or from those having black-tipped wings 

 by the peculiar color pattern of the primaries. Birds in immature 

 plumage are not so easily recognized, but a careful study of the 

 descriptions given in the manuals will help to identify them. They 

 are not likely to be confused with the dark-mantled western gull, 

 174785—21 6 



