136 A HISTORY OF BIRDS 



four miles wide. The birds arrived in two separate bodies, one 

 directly from the south by land, the other following the east 

 coast of Wisconsin, and crossing Manitou Island, the latter 

 body forming an army at least five miles long and one mile 

 broad. The birds at once began the work of nest-building, and 

 in a very short time this colony extended for a distance of 

 about twenty-eight miles of forest, every tree having one or 

 more nests, and some being filled therewith ! 



It is clear that large assemblages of the same species are 

 only possible when there is an abundance of food for all, and 

 the gregariousness of some birds is probably due to this fact 

 alone, as in the case of Gannets and Guillemots, for example, 

 or the large gatherings of birds of prey, as when following the 

 hordes of migrating Lemmings. It does not seem that such 

 assemblages are bound by any ties of mutual affection or for 

 desire of protection, though these several inducements cannot by 

 any means be sharply divided. Parrots, for example, appear to 

 roam in bands for the mere pleasure of company; while Rooks 

 find in association security against surprise while engrossed in 

 feeding, since one or other of the flock is constantly performing 

 the role of sentinel. The vagrant bands of the Long-tailed 

 Titmouse, which lend such a charm to our woods during the 

 autumn and winter months, are held together very largely at 

 any rate by their common needs. The discovery of insect food 

 at this time is an arduous task, and if undertaken individually 

 many would starve. As Professor Newton remarks : " A single 

 Titmouse searching alone might hunt for a whole day without 

 meeting with a sufficiency, while if a dozen are united by the 

 same motive, it is hardly possible for the place in which the 

 food is lodged to escape their detection, and when discovered 

 a few call-notes from the lucky finder are enough to assemble 

 the whole company to share the feast. . . . One tree after 

 another is visited by the active little rovers, and its branches 

 examined : if nothing be forthcoming, away goes the explorer 

 to the next that presents itself, merely giving utterance to the 

 usual twitter that serves to keep the body together. But if 

 the object of the search be found, another kind of chirp is 

 emitted, and the next moment the several members of the 

 band are flitting in succession to the tree, and eagerly engaged 

 with the spoil." 



