Causes of the Migrations of Birds. 147 



fore this species in particular should annually roam so far 

 beyond the region frequented by its compeers. Why does it 

 not content itself with the eternal summer of the south, instead 

 of forming the exception, and hurrying north as soon as the 

 weather will allow, to enjoy a short-lived warm season in 

 Labrador or Newfoundland, where it has scarcely time to rear 

 its young before the time comes for the retrograde movement? 



All we can say is that some inherited instinct is at work, 

 perhaps to them as precious as is the longing for the holidays 

 to the schoolboy, full of pleasant reminiscences, which of course 

 would grow by experience; and judging from the mute and 

 inert lives many migratory birds, to my knowledge, do pass 

 in their winter quarters, it may be birds, like human beings, 

 love change. 



The sexual instinct has sometimes appeared to me to be 

 either a direct cause or a direct effect of the migratory bird's 

 movements ; perhaps in such as lag long in winter quarters it 

 may hasten departure ; but, as elsewhere observed, I have 

 found that few birds on the way to their summer retreats show 

 that enlargement of the sexual organs observed during 

 courtship and nidification. On this account I have been dis- 

 posed to think that the aphrodisiacal tendency is not always 

 the exciting cause, although it may occasionally influence the 

 movements of certain species.* 



The Warblers which frequent these woods in summer are 

 numerous ; and as regards habits, there is little to add that 

 is not common to the majority. I must therefore refer the 

 reader to the list of birds of the region at the termination of 

 this volume. There are a few, however, which I may briefly 

 allude to, more especially with reference to their numbers and 

 geographical distributions. No doubt when the country is 

 more opened out and the forests cleared, and extensive culti- 

 vated tracts are formed, many species will increase in numbers. 

 Moreover (as we have seen) many birds formerly confined to the 



* " Natural History and Archaeology of Lower Nile Valley and Malta," 

 pp. 12, 102, and 106. 



