MILITARY TACTICS OF ANIMALS 55 



are probably due to corresponding changes in the 

 force or direction of the wind, affecting simultane- 

 ously all the birds of the flock. But for determining 

 the causes of these ordered changes in the aerial 

 tactics of birds, a body of observation has yet to be 

 obtained, for which London, with its parks and lakes 

 and wild fowl, offers unusual facilities. 



