-128 THE NATURAL HISTORY OF SELBORNE. 
associations do take place in hard weather chiefly, and thicken 
as the severity increases. As some kind of self-interest and 
self-defence is no doubt the motive for the proceeding, may it 
not arise from the helplessness of their state in such rigorous 
seasons ; as men crowd together, when under great calamities, 
though they know not why? Perhaps approximation may 
dispel some degree of cold ; and a crowd may make each indi- 
vidual appear safer from the ravages of birds of prey and other 
dangers. 
If I admire when I see how much congenerous birds love to 
congregate, | am the more struck when I see incongruous ones 
in such strict amity. If we do not much wonder to see a flock 
of rooks usually attended by a train of daws, yet it is strange 
that the former should so frequently have a flight of starlings 
for their satellites. Is it because rooks have a more discerning 
scent than their attendants, and can lead them to spots more 
productive of food? Anatomists say that rooks, by reason of 
two large nerves which run down between the eyes into the 
upper mandible, have a more delicate feeling in their beaks 
than other round-billed birds, and can grope for their meat 
when out of sight. Perhaps, then, their associates attend them 
on the motive of interest, as greyhounds wait on the motions 
of their finders, and as lions are said to do on the yelping of 
jackals. Lapwings and starlings sometimes associate. 
LETTER XII. 
March 9th, 1772. 
As a gentleman and myself were walking on the 4th of last 
November round the sea-banks at Newhaven, near the mouth 
of the Lewes river, in pursuit of natural knowledge, we were 
surprised to see three house-swallows gliding very swiftly by 
us. ‘That morning was rather chilly, with the wind at north- 
