2io THE POPULAR SCIENCE MONTHLY 



I 



/ 





\ A., \ ^ 



y 



Destination D 



B 



FLYINC SEPARATELY FLYINC IN A FLOCK 



Fig. 1. In the left-hand diagram, A, the arrows are intended to represent birds 

 and the directions in which each individual would fly if alone. Thus they indicate 

 the amount of confusion of each bird with respect to the true destination D. In the 

 right-hand diagram B, the birds are represented flying in a flock, the errors of 

 orientation having been averaged by mutual reaction as indicated by the parallel 

 arrows. 



The large flock seems to eliminate these causes of error to a con- 

 siderable extent, therefore it is probable that the origin of the flocking 

 custom is largely due to the fact that it is protective. 



The explanation suggested by the author to account for the flocking 

 habit is as follows : 



The Direction Errors of the Individuals of the Flocx are 



Averaged 



If, for example, in the case of a migrating flock, there are any indi- 

 viduals that are confused in their bearings with respect to the direction 

 of their destination, and there must be many that are more or less con- 

 fused, some erring toward the right, some toward the left, the errors of 

 the individuals of the flock are automatically averaged and corrected by 

 imitation, and by mutual reaction by those same individuals. 



According to this hypothesis, birds flying in a flock will follow the 

 direction which may be called the mean flight direction of the flock. 

 The idea is illustrated by a diagram. In Fig. 1, A, the arrows attached 

 to circles are meant to represent the directions that the individual birds 

 of a migrating flock would take, for example, after resting on an open 

 sea, and arising to fly to an intended destination, D, (Fig.), provided 

 each individual was required to migrate alone from that moment. The 

 assumption is made that most of the birds are confused with respect to 



