126 FLEAS, FLUKES AND CUCKOOS 



Mallophaga and their eggs, and tends to restrict egg-laying mainly to 

 the head and neck, or to a modified form on the wing feathers. A 

 specimen of the cuckoo head louse {Cuculoecus latifrons) was recently 

 found on the back of a cuckoo in a damaged condition — the thorax and 

 abdomen being attached to one feather, and the severed head to an 

 adjacent one. The louse presumably had strayed from the safety of its 

 normal habitat, and was torn in two during the preening of the back 

 feathers. Further evidence of the importance of preening is shown by 

 the case of a robin which had most of the upper mandible of the bill 

 missing; it was infested with 127 specimens of Ricinus rubeculae, the 

 numbers of which rarely exceed 15 on any one bird. 



The choice of habitat, the structural modifications of the louse and 

 the position of the egg-laying sites, have probably been largely deter- 

 mined by the preening habits of birds. It is interesting to speculate 

 whether the apparent colour adaptations of some lice to the feather 

 background on which they live are true cases of adaptive colouration. 

 Are they protected from the bird in the same way as the woodcock, 

 whose plumage merges with the dead leaves and bracken amongst which 

 it lives, is protected from carnivorous predators ? There are many 

 instances of a resemblance between the colour of the louse and the 

 plumage of its host: white lice on the white gulls and darker lice on the 

 darker but related skuas ; white lice on the white swan, dark lice on the 

 black swan; a yellow louse on the golden oriole, a black one on the 

 coot. Such examples could be multiplied almost indefinitely. It has 

 been suggested that the yellow colour of the golden oriole louse is due 

 to the fact that it eats the substance which gives the feather its yellow 

 colour. There is no proof of this, and it is an explanation which cannot 

 be applied to such cases as the white swans and gulls, which in addition 

 to lightly coloured lice, also have other species which are brown and 

 sometimes exceptionally dark in colour. These dark species, it should 

 be noted, are confined to the head and neck where they are out of reach 

 of the beak. It seems probable that certain genera of feather lice, like 

 the last nymphal instars of the human sucking louse, have the ability to 

 respond to the colour of their background. It is not known, however, if 

 the resulting similarity in colour between the louse and the feather on 

 which it lives does in fact serve a protective purpose. 



Bathing in water and dust and the subsequent preening (Plate VIII) 

 helps the bird to rid itself of parasites. Lice have been found in the 

 dust taken from dust baths habitually used by chickens. As Pliny 



