6878 Birds. 



what is perhaps the principal object, avoid the heavy rains, fogs and 

 cold of the nights and mornings, and find within a short distance all 

 the circumstances which combine to produce a plentiful supply of 

 prey, — a change evidently quite as adapted to the bird's wants as 

 that which the swifts that wheel round the church towers of England 

 obtain after a distant migration. That the distance of a migration is 

 very short, is not a reason why it may not be very effective, if these 

 circumstances be taken into consideration. Many more instances in 

 favour of this might be advanced, and I am inclined to think that the 

 further our observations are extended the more will the existence of 

 this double migration in the tropics be recognised — the one external, 

 or a migration of latitude ; the other internal, or a migration of alti- 

 tude. In the latter the observer of Nature may see, passing as it 

 were before his eyes, a representation of the former. Lines, however, 

 representing the boundaries of the summer range of these three spe- 

 cies, would by no means maintain the same coincidence. 



" Ptilogonys certainly leaves the mountains of Trelawny during the 

 summer, though their elevation is not less than 3000 feet, and, from 

 information collected in your work, appears to be confined, for that 

 season, to the still higher chains of this end. 



" Hirundo euchrysea 1 found at Freeman's Hall in solitary pairs, 

 and but few of them. 



" The line indicated can only be comparatively called the winter 

 boundary of Acanthylis, as the powers of flight of these birds are so 

 great, and their habits lead them to take so wide a range, that pro- 

 bably during the whole summer, under certain conditions of weather, 

 &c., they visit at intervals their winter haunts. 



" I have given these observations in some detail, because they seem 

 of more than mere theoretical importance. The case of a naturalist 

 may easily be supposed whom circumstances led to the southern foot 

 of the central range during the cold months. He might there see, 

 once or twice, H. euchrysea, and procure specimens; he then might 

 pass a whole year on the South coast, and even travel extensively on 

 the North coast, without again falling in with them, and thus be led 

 to conclude them to be stragglers from some external migration, 

 when they really only travel up and down the mountains. 



" A seventh species of Hirundine must be added to our Jamaica 

 list. I saw it once, at Falmouth, on the coast. May, 1859, and early 

 in the following October at Llandovery Estate, St. Ann's, close to the 

 sea, and a third time here on the 15th of November last. It is imme- 

 diately distinguished from H. pceciloma, which it most resembles, by 



