LIFE HISTORIES OF NORTH AMERICAN" GULLS AND TERNS. 113 



Occasionally, however, their flight is in a long- line, one behind the 

 other, or in broad lines abreast, and rarely they may be seen in the 

 typical V formation of ducks. In rising, a flock often ascends 

 nearly vertically in a great circle all together, or in many intersect- 

 ing circles. The play of light and shade, of sun and shadow, alter- 

 nately make the birds appear dark and light. Many hours are spent 

 by the gulls in this graceful and beautiful sport of soaring in circles — 

 a sport which apparently requires but little effort, as, under favor- 

 able conditions, few wing beats are necessary. The descent may be 

 made in the same manner as the ascent by circling, but at times the 

 birds drop swiftly down by tipping or rocking from side to side. 



In windy weather the flight of the herring gull is far from slow 

 and heron-like. Then it is extremely graceful, as the bird alter- 

 nately sails with great rapidity before the wind or beats up into it. 



At times these gulls are able to sail directly into the teeth of the 

 wind without a single stroke of the wing. Mr. William Brewster 

 (1912) has described the manner in which herring gulls keep pace 

 with a vessel, gliding along on almost motionless wings into the teeth 

 of the gale, sometimes within a few yards of the deck, but always 

 on the windward side. He says : 



As the gale increased they flapped their wings less and less often, until most, 

 if not all of them, were gliding ceaselessly, minute after minute, over distances 

 certainly exceeding a mile, without a single v/ing beat, but not without changes 

 or readjustments in the bend or the inclination of the wings, which took place 

 not infrequently and often were very obvious. 



Several explanations of this mysterious means of propulsion have 

 been offered, but the following by F. W. Headley (1912) seems to me 

 the most satisfactory. He says : 



There is a feat perhaps more striking than any of the others already de- 

 scribed — a feat which, nevertheless, gulls often achieve. A steamer is advanc- 

 ing against a fairly strong wind, which, if not absolutely a head wind, strikes 

 the vessel at an acute angle. There results a st(>ady up current over the stern 

 of the vessel, or slightly to one side or the other of the stern. Poised on this 

 up current the gulls hang in mid-air, their wings held rigidly expanded. Only 

 very slight wing movements, evidently for purposes of balance, can be detected. 

 Standing on the deck and watching these gulls one is irresistibly reminded of 

 tlic poising of the kestrel high in air, with wings held motionless, when he finds 

 a wind that is all that he could wish. It is sometimes easy to forget that, 

 unlike the kestrel, they do not remain in one spot, but that all the while they 

 are moving forward and, in fact, keeping pace with the steamer. The gulls, 

 like the kestrel, are poising on an up current of air; but they give their bodies 

 a rather different incline, with the result that they keep traveling forward. 

 * * * The general incline of their body and wing surfaces is slightly down- 

 ward. Hence the upward-streaming wind not only maintains them in the air 

 or lifts them higher, but, acting at right angle, also drives them forward. 



A similar explanation is given in detail by A. Forbes (1913). 



