Birds. 6877 



a half from the beach, and the trees on which the bird was singing 

 can hardly be two hundred feet above the sea. 



"Mr. Hill ('Birds of Jamaica,' p. 56) considers Acanthylis only an 

 occasional visitor to the South-east. Your observations established 

 the same fact for the South-western coast. I found them more com- 

 mon, during the winter, at Mahogany Hall (about 1000 feet) ; but in 

 Metcalfe, at the same season, they are constantly to be seen close to 

 the sea. 



"Hirundo euchrysea is so brilliant a little bird that it is almost im- 

 possible it could escape an observer of Nature, even were its visits 

 very rare. But Mr. Hill is quite silent as to its occurrence in his 

 neighbourhood. It escaped your observation for two winters, mine for 

 one, in the South-west, though I afterwards saw it close to the 

 southern base of the central range at Oxford, in Manchester. At 

 Mahogany, at this season, I found them appearing, at intervals, in 

 large flocks ; but here the same flocks hunt on fine mornings along 

 the coast. 



" Ptilogonys, I think there can scarcely be a doubt, occurs, during 

 the winter, on the South side only, at the elevation you discovered it, 

 2600 feet. I met with them in Trelawny at a height I should esti- 

 mate at least at 1000 feet less, and here they may be heard at a very 

 slight elevation above the sea. 



" And thus, were we to trace on the map lines representing the 

 boundaries of the different winter migrations of all three species, they 

 would singularly coincide : the great basins of the South side would 

 be cut off" the lines, keeping close to the central range, or including 

 only lofty spurs ; whilst on the North side they would descend much 

 nearer the coast, keep at a less elevation, and as the mountains 

 increased in height and the lowlands shrunk in extent they would 

 finally coincide with the coast-line. 



" Hence it appears that these mountain species, though they do not 

 frequent the hot South-side plains and coasts, during the winter 

 migrate downwards to a certain temperature. And should we be sur- 

 prised at this? The influence of altitude on temperature, — an 

 influence which intensifies as we approach the tropics, — is fully 

 recognised in other departments of Science, and perhaps is less so in 

 Ornithology, only because observation in the tropics, where it is 

 likely to be most felt, are made with greater difficulty and to a less 

 extent than elsewhere. But it should be borne in mind that the 

 Hirundines, in migrating downwards as the winter approaches, pro- 

 bably gain an increase of teuiperature of fifteen or twenty degrees, or, 



