FEATHER LICE I25 



condition and plumage, was found to have 1,803 ^ice, another from 

 Suffolk, 1,047, and a rook from Wiltshire just over 300. These numbers 

 are unusually high, although the curlew is always found to harbour 

 some lice, usually between 50 and 200. In the case of the small passer- 

 ines, many individuals seem to be louseless, or the numbers found are 

 small, usually between one and ten in number — over twenty lice is 

 uncommon. Young birds tend to be more heavily infested than adults 

 and sick birds more than healthy ones. The world record is held by an 

 East African cormorant [Phalacrocorax nigrogularis) which harboured 

 over 7,000. It is doubtful if there is any species of bird in the world 

 which is without at least one kind of feather louse. This pained the 

 early entomologists, one of whom remarked that "even the gorgeous 

 peacock is infested by one of extraordinary dimensions and singular 

 form"; and Benjamin Franklin ruefully laments the choice of the bald 

 eagle as the emblem of America : "as he is generally poor and often 

 very lousy." 



The population of lice may be large without apparently harming 

 the bird, but when it is abnormally heavy, in sick, captive, or young 

 birds, the effect on the host may be serious. The mere movement of the 

 lice is intensely irritating, so that the bird damages itself by excessive 

 scratching. The lice, if too numerous, may denude some of the feather 

 shafts, and cause injury and loss of blood by rupturing the skin during 

 feeding. The punctures made in the feathers when in quill, by the 

 chicken louse, may inhibit their development altogether. 



The Mallophaga, up to the present, have never been convicted as 

 effective carriers of any disease, a fact which is reflected in the small 

 amount known about their biology compared to the typhus-carrying 

 sucking louse and the plague-carrying flea. One of the mammal 

 Mallophaga, that of the dog, acts as the intermediate host of a tape- 

 worm; and there is a single record of a bird Mallophaga [Dennyus] 

 acting as the intermediate host of a roundworm {Filaria), which 

 parasitises the bird host, a swift. Further work may reveal other cases 

 of parasites which spend part of their life-cycle in the host and part in 

 the louse. 



Factors Limiting Population Size. The fact that birds tend to be 

 more heavily infested if they are sick suggests that, by their own 

 efforts, they normally help to keep the louse population in check. 

 Preening by the bird (Plate VIII) doubtless eliminates a number of 



