100 NATURAL HISTORY 



LETTER XL. 



TO THE SAME. 



Selborne, Sept. 2, 1774. 

 DEAR SIR, 



BEFORE your letter arrived, and of my own accord, I had been 

 remarking and comparing the tails of the male and female 

 swallow, and this ere any young broods appeared ; so that 

 there was no danger of confounding the dams with their pulli: 

 and besides, as they were then always in pairs, and busied in 

 the employ of nidification, there could be no room for mistak- 

 ing the sexes, nor the individuals of different chimnies the one 

 for the other. From all my observations, it constantly ap- 

 peared that each sex has the long feathers in it's tail that give 

 it that forked shape ; with this difference, that they are longer 

 in the tail of the male than in that of the female. 



Nightingales, when their young first come abroad, and are 

 helpless, make a plaintive and a jarring noise ; and also a 

 snapping or cracking, pursuing people along the hedges as 

 they walk : these last sounds seem intended for menace and 

 defiance. 



The grasshopper-lark chirps all night in the height of sum- 

 mer. 



Swans turn white the second year, and breed the third. 



Weasels prey on moles, as appears by their being sometimes 

 caught in mole-traps. 



Sparrow-hawks sometimes breed in old crows' nests, and 

 the kestril in churches and ruins. 



There are supposed to be two sorts of eels in the island of 

 Ely. The threads sometimes discovered in eels are perhaps their 

 young : the generation of eels is very dark and mysterious*. 



Hen-harriers breed on the ground, and seem never to settle 

 on trees. 



When redstarts shake their tails they move them horizon- 



* [For a complete elucidation of this subject see Yarrell's Brit Fishes 

 ii. 289. T.B.] 



