THE SWALLOWS AG A IX. 51 



and thrive upon insects alone ; being, in fact, as he puts 

 it, still in the swift stage of their development. 



As for the points of convergence between the hum- 

 ming-birds and the sun-birds, those are easily enough 

 explained. Both races feed upon long-tubed tropical 

 flowers, probing their recesses in search either of honey 

 or flies ; and both, consequently, require long bills and 

 extensile tongues. Both races also possess brilliant 

 plumage, with metallic crests or gorgets ; and such 

 brilliance is common amongst all flower-feeding and 

 fruit-eating species, such as butterflies, rose- beetles, 

 toucans, parrots, and birds of paradise. The constant 

 association with coloured objects, and the constant 

 search for them as food, seems to arouse a taste for 

 bright colour in the creatures themselves, which is ac- 

 tively exerted in the choice of mates. Why some 

 members of the swift and swallow family should have 

 undergone this change to humming-birds in the western 

 continent and not in the eastern would be a more diffi- 

 cult question to answer offhand ; but I fancy the differ- 

 ence may be partly due to two causes. In the first 

 place, the peculiar way in which the Old World is cut 

 up into two distinct regions, hot and cold, by the Me- 

 diterranean and the Himalayan range may have favoured 

 extensive migration here ; while in America the con- 

 tinuity of land, the warmth of summer, and the general 

 luxuriance of blossoms permit humming-birds to range 

 as far north as Canada ; and thus one continent may 

 have favoured only the old open insect-hunting types 

 like the swift, while the other favoured also specialised 

 flower-haunting types like the humming-birds. In the 

 second place, the creepers may already have occupied 



£ 2 



