28 FLEAS, FLUKES AND CUCKOOS 



Some biologists, however, believe that the birds merely get an enjoyable 

 sensual pleasure from the movements of the ants among the feathers, or 

 from the stimulus of formic acid on the skin. It is a well-known fact 

 that tame parrots and owls enjoy having their necks tickled. One tame 

 parrot developed the habit of pushing a piece of apple under its wings 

 or into the back between the shoulders; it was suggested that the acid 

 in the apple cooled or stimulated the skin. Finally those who favour 

 the theory of odour-attraction believe that the bird is scenting itself and 

 that the smell of the formic acid or aromatic oils are a source of pleasure 

 and satisfaction. Although there is as yet no conclusive explanation 

 of the habit of "anting," Chisholm, who has studied and reviewed the 

 subject (1944), considers that the value of the acid as a skin stimulant 

 is the most potent factor. An indirect result which springs from the 

 presence of acids on the feathers is the death of the parasites. It 

 seems possible that the habit may have arisen from birds taking dust 

 baths in the loose earth found on ants' nests, and the additional 

 stimulus and cleansing power of the formic acid was appreciated. 

 Again, many birds when sunning themselves take up the passive anting 

 position (Plate IVb) and the habit may have been initiated by birds 

 sunning themselves in the vicinity of ants' nests. " Howe handsome 

 it is to lye and sleepe, or to lowze themselves in the sunn-shine." 



Little definite information is available about any other factors 

 which limit population size. There may be competition between the 

 different species on one host (interspecific competition) or between 

 the individuals of one species (intraspecific competition). Waterston 

 records finding a specimen of Goniodes (a large louse from game- 

 birds) with its crop crammed with pieces of Goniocotes, a consider- 

 ably smaller louse. Mites, when numerous, may also keep down the 

 number of Mallophaga, possibly by the destruction of the eggs, for 

 empty egg-shells have been found occupied by mites. 



Little is known about the diseases which attack the Mallophaga. 

 Occasionally parasitic fungi have been observed in the form of colour- 

 less club-shaped projections on the bodies of the larger lice, and it is 

 probable that they are in some way harmful to the host. Mites and their 

 eggs are also found attached to feather lice. These mites, which belong 

 to a genus peculiar to the Mallophaga and closely related to another 

 genus found on the louse-flies, have been recorded from Trinoton 

 (Plate XXII) and Ancistrona only, which are particularly large in size. 

 They seem to be relatively harmless. Thus in the case of some of the larger 



