FLOCKING HABIT OF NIGRA TING BIRDS 2 1 5 



or air pressure as in the closely formed flocks during the day. That 

 countless numbers of birds migrate at night has been abundantly 

 demonstrated and requires no proof. 



The Protective FtfRM of Certain Flight Formations 



The flight formations of birds which fly in flocks vary greatly with 

 different species, so varying is it that in many cases it is an identifying 

 characteristic. Many small land birds fly in very compact groups, 

 examples of which are the various species of blackbirds, grackels, cedar 

 birds, finches, etc. Many water birds fly in compact flocks. Moreover, 

 for many species there seems to be some general law regarding the size 

 of the bird and the distance apart of the different individuals of the flock. 



Probable Explanation of the Echelon Formation 



The most distinctive formation is the echelon arrangement of flight 

 and deserves special attention. Many of the larger water birds such as 

 geese, many species of ducks, flamingoes, etc., practise this method of 

 flight. The formation, according to one explanation, owes its origin 

 to the fact that such an arrangement prevents swirls in the air pro- 

 duced by the wings of one bird from interfering with the next bird 

 following. This may be true to some extent, but the explanation which 

 the author holds as far more likely is that the formation is chiefly, if not 

 wholly, a protective arrangement, and is, in fact, the only one in which the 

 individual birds of the flock, if they are of considerable size, can see 

 both forward and to the side at the same time, as demonstrated by the 



Fig. 7. Flock of Bi.uk Geese in Echelon Formation, photographed by the) 

 Rev. H. K. Job. As in Fig. 6, for each goose, the view is unobstructed in front and 

 at right angles to the line of flight. 



