FLOCKING HABIT OF MIGRATING BIRDS 2 1 7 



has been given by others, but the author has not found it in other 

 writings. Small birds that pursue an irregular flight (i. e., undulating 

 or fluttering) have an opportunity to see into the danger zones even 

 when in a large flock; hence the necessity is lacking for the echelon 

 arrangement of the individuals of a flock in such cases. 



Among certain species of ducks a reverse echelon flight formation is 

 observed, namely, the directions of flight is in the opposite direction to 

 the point of the V. The reverse V is nearly as protective as the V. 

 Since in this form also the number of eyes of the birds in the flock which 

 cover the "danger zone" is at a maximum. The above hypothesis does 

 not in any way conflict with the theory that geese will follow a leader, 

 a theory which may or may not be true. 



The facts presented above are taken as strong arguments for the con- 

 clusion that the origin of the flocking habit is due to its protective 

 effects, and that particularly the echelon arrangement of flight has been 

 evolved from the protection against enemies which it affords. 



This investigation has been aided by a grant from the Herman Fund 

 of the New York Academv of Sciences. 



