254 BULLETIN 130, UNITED STATES NATIONAL MUSEUM 



winged sea ducks. It has a parallel in the flight of the emperor goose except 

 that the latter is a far heavier bird and, in consequence, the wing strokes are 

 less rapid. In B. nigricans tlie strokes are short, energetic, and repeated with 

 great rapidity, carrying the bird with a velocity far greater than that attained 

 by any other goose with which I am acquainted, thougli probably its eastern 

 prototype equals it in this respect. 



But this is not the point upon which the mind rests when the birds are in 

 view, for then the eye is held in involuntary admiration of the varied and 

 graceful evolutions of the flocks, which have a protean ability to change their 

 form without ever breaking the array or causing confusion. They are very 

 gregarious, and two flocks almost invariably coalesce when they draw near 

 each other. This frequently occurs until, as I have seen, it results in a 

 single flock numbering betvteen 400 and 500 birds. The usual size is consid- 

 erably less, generally comprising from 20 to 50 or more, and it is rare to 

 see less than 10 or 15 in a party. At times 4 or 5 individuals become de- 

 tached, and until they can unite with a stronger party they fly irregularly 

 about as though bewildered, continually uttering their harsh notes, and hurry 

 eagerly away to join the first flock that comes in view. The order of flight 

 is invariably a single rank, the birds moving side by side in a line at right 

 angles to their course so that the entire strength of a flock is to be seen at 

 a glance along its front, which at times covers several hundred yards. There 

 is barely room enough between the individuals to allow a free wing stroke. 

 Thus ranged, the flock seems governed by a single impulse, which sends it 

 gliding along parallel and close to the ground, then, apparently without reason, 

 careering 30 or 40 yards overhead, only to descend to its former level as 

 suddenly as it was left ; now it sways to one side and then to the other, 

 while at short intervals swift undulations seem to run from one end of the 

 line to the other. These movements are repeatedly taking place; they are 

 extremely interesting to observe but difficult, I fear, to convey an adequate 

 idea of in words. 



The entire flock, consisting of perhaps over a hundred birds arranged in 

 single line, is hurrying on, straight as an arrow, toward its destination, when, 

 without warning, it suddenly makes a wide curving detour of several hundred 

 yards, then resumes its original course only to frequently repeat the maneuver, 

 but always with such unison that the closest scrutiny fails to reveal the least 

 break or irregularity in the line ; nor does the front of the flock swerve, 

 excepting an occasional slight obliquity which is corrected in a few seconds. 



In addition to this horizontal movement is a still more interesting vertical 

 one which often occurs at the same time as the other but generally by itself. 

 A bird at either end of the flock rises or descends a few inches or several 

 feet, as the case may be, and the movement is instantly followed in succession 

 by every one of its companions till the extreme bird is reached and the entire 

 flock is on the new level ; or it may be that a bird near the middle of the line 

 changes its position, when the motion extends in two directions at once. 

 These latter changes are made so regularly and with such rapidity that the 

 distance between the birds does not appear altered in the least, while a 

 motion exactly like a graceful undulation runs the length of the flock, lifting 

 or depressing it to the level of the originator of the movement. These changes 

 present to one's eye as the flocks approach, keeping close to the ground, the 

 appearance of a series of regular and swift waving motions such as pass 

 along a pennant in a slight breeze. 



The black brant never wings its way far up in the sky, as many other 

 geese have the habit of doing, but keeps, as a rule, between 10 and 30 yards 

 above the ground, with more flocks below these limits than above them. 



