Page:Popular Science Monthly Volume 84.djvu/221

Rh 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 conclusion 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 Academy of Sciences.