FLOCKING HABIT OF MIGRATING BIRDS 



21 1 



the correct orientation to a greater or less extent, which is obviously the 

 fact, although the confusion may be very slight in some cases. In Fig. 

 1, B, the direction in which the birds will actually move when in flight 

 as a flock is indicated by the parallel arrows. Thus in Fig. 1, B, the 

 mutually related influence of the individuals prevents the dispersion 

 that would occur as indicated by the direction of the arrows in Fig. 1, A. 

 The averaging of the errors that take place, as indicated in B, is ap- 

 proximately governed by mathematical certainty, and as a matter of 

 fact, in the drawing Fig. 1, B, the flight direction was determined by 

 taking the mean of all the directions indicated by the arrows in "A." 



Each bird is affected by the averaging of flight directions due to the 

 mutual reaction of the individuals, and the reaction prevents false 

 starts. As an extreme case of this correcting influence, consider a 

 flock of birds proceeding northward after resting on an open sea in a 

 fog ; and suppose that one bird was so confused that it would have flown 

 in the opposite direction (to the south) if alone. Then, in all prob- 

 ability, in spite of its individual inclination to fly south, this bird would 

 be carried northward with the flock by the powerful principle of 

 imitation. 



It must be distinctly understood that this theory does not give an 

 explanation of the sense of direction, but it does provide a mechanism 

 which will prevent individuals of the flock from getting lost. The only 

 assumption is that there are all degrees of right and wrong " bearings " 

 among the individual birds of the flock. 



Land 



Ocea 



Destination 



B 



FLYING SEPARATELY 



FLYINC IN A FLOCK 



Fig. 2. The curved lines in the left-hand diagram A represent the paths which 

 the birds would follow due to unequal unbalanced wing power, if each was alone. In 

 the right-hand diagram, B, the arrows represent the birds flying together and the di- 

 rection is the mean of all deviations and represents the flight direction towards D as 

 corrected by mutual reaction. 



