LETTER XXI. 



To the same. 



SELBORNE, Sept, 2%t6, 1774. 



EAR SIR, As the swift or black martin is the 

 largest of the British bir undines? so it is undoubt- 

 edly the latest comer. For I remember but one 

 instance of its appearing before the last week in 

 April ; and in some of our late frosty, harsh 

 springs, it has not been seen till the beginning of 

 May. This species usually arrives in pairs. 

 The swift, like the sand-martin, is very defective in architecture, 

 making no crust, or shell, for its nest ; but forming it of dry grasses 

 and feathers, very rudely and inartificially put together. With all 

 my attention to these birds, I have never been able once to discover 

 one in the act of collecting or carrying in materials ; so that I have 

 suspected (since their nests are exactly the same) that they sometimes 



1 As I have already noted, the swift is now known to belong to an entirely 

 different group of birds from the swallows, being in reality much more closely 

 related to the tropical humming-birds. Its apparent resemblance to the swallow 

 tribe is purely adaptive, and results only from similarity of habits. Mr. Alfred 

 Russel Wallace has worked up this question admirably in his " Tropical Nature." 

 En. 



Q. 



