252 FLEAS, FLUKES AND CUCKOOS 



the latter's nests, but uncommon in the former's, where mites take their 

 place as a dominant group. 



It will have become evident from this brief account, mainly of the 

 fauna of martins' and swallows' nests, that the bird-lovers who carefully 

 preserve their habitations from one year to another also unintentionally 

 preserve the louse-flies, fleas, mites and bugs over-wintering as larvae 

 and pupae or hibernating in the nest, which are directly responsible for 

 bringing hours of pain, miser\% disease or even death to the nestlings in 

 the following spring. Under these circumstances it seems astonishing 

 that birds returning from their winter quarters, especially those which 

 feed on insects, do not rid their own nests of nidicoles before reoccupying 

 them. They are, however, creatures of habit and inflexible instincts. 

 Hedge-sparrows and other species (see p. 261) will let their own young 

 die of star\'ation if they are shifted from the inside to the edge of their 

 nests. In such a position they are not recognised as nestlings and are 

 not fed. It is possible that birds do not associate food-hunting with the 

 nest, but in its presence respond to a strong instinct to be unobtrusive 

 and quiet, and to disturb it as little as possible. They may not, there- 

 fore, recognise the nidicoles as food. Furthermore, these arthropods 

 may be highly unpalatable. The smell of bed-bugs does not suggest that 

 they would form an attractive breakfast. On the other hand, recent 

 visual obser\'ations made on rooks during sexual display and courtship 

 in the rookerv^ in winter show that they obtain a considerable amount of 

 food from their nests. The photograph on Plate XXXMI of a whitethroat 

 is a source of speculation. "WTiat, in fact, is it doing? Removing faeces 

 from the nest or routing out nidicoles? Possibly birds do destroy num- 

 bers of these arthropods. In any case it is an aspect of bird behaviour 

 about which little, if anything, is known and it should prove yet 

 another interesting and fruitful source of study. 



