THE WARBLERS. 1 09 



Cashmere, Central Asia or Europe. In the cold 

 season they turn southwards again and diffuse 

 themselves over every corner of India. Many 

 reasons have been assigned for this strange " mi- 

 gratory instinct," as it is called, which affects so 

 many species of birds. No philosopher, as far as 

 I know, has bestowed as much thought upon this 

 same instinct as it manifests itself in Viceroys and 

 Governors, members of Council, wives and other spe- 

 cies of the genus Homo. To me the matter appears to 

 lie in a nutshell. When a place becomes too hot, ortoo 

 cold, or too wet, the inhabitants feel a very natural in- 

 clination to leave it and go to some place which is more 

 comfortable. And they do so. Not all; some humble 

 creatures, muskrats, for example, and frogs and 

 toads and husbands and some others, cannot get 

 away. Others are kept back by a love of home, 

 or a disinclination for change. But those that can 

 go generally do go, and so it grows into a fashion. 

 Among birds a fashion soon acquires a hereditary 

 force and we call it an instinct. In the case of the 

 Tree Warblers there is a simple and all-sufficient 

 reason for this annual journey southwards, which is, 

 that if they remained they would starve. Birds that 

 live entirely on small, soft-bodied insects, cannot 

 afford to spend the winter in a climate in which the 

 lower forms of life almost cease during that season. 

 But in the tropics there is no time of the year when 

 spiders and little insects of many kinds may not be 

 had. So to the tropics they go, as Jacob and his 

 family went to Egypt. And in every green tree, at 

 almost any hour of the day, you may see them hop- 

 ping from twig to twig, flitting, clinging, looking 



