100 FLEAS, FLUKES AND CUCKOOS 



body has provided the feather hce with a more or less constant environ- 

 ment and one which has altered them less than the impact with the 

 outside world has altered the host itself. Therefore, the relationships of 

 the parasites often throw light on the relationships of the birds. 



In mammal fleas, although they are altogether much less closely 

 bound to their hosts than feather lice, and in the larval stages also have 

 to cope with climatic and other outside influences, the same type of 

 phenomenon can be observed. For example the extraordinary and 

 unique group of fleas known as the helmet fleas of Australian marsupials 

 are also found on the pouched mammals of South America, thus once 

 again confirming the latter's true relationship with the Austrahan 

 marsupials and demonstrating their common origins. 



The situation in the case of the bird fleas is, however, very different. 

 The change over to birds is altogether too recent to provide evidence of 

 host relationship. What these fleas often provide, however, is a clue to 

 the past geographical history of the bird. For example the European 

 chough fleas [Frontopsylla frontalis and F, laetus"^) which may still be added 

 to the British list are descended from a genus of the Amphipsyllidae, a 

 family of fleas from Central Asia and China. The choughs are con- 

 sidered by many ornithologists to be a strictly Asiatic group which has 

 extended its range into Europe some time during the Pleistocene, so 

 the presence of these fleas supports their theory. The penguins breeding 

 in the Australian and South African areas have fleas clearly of South 

 American origins and this indicates from which area these birds 

 extended their range eastwards. Other examples of this type could be 

 given, but sad to say here again no definite conclusions can be drawn 

 from the British fauna, because not enough is known about the fleas 

 of our own birds. It is amazing how little collecting of bird fleas has 

 been done by British ornithologists, especially if one considers the 

 attention now given to almost every aspect and detail of bird fife. 



Host Specificity and Host Preference 



Among bird fleas there are three main types of host preference. 

 The first and most obvious is when a species of flea is adapted to one 

 species of bird only — in other words it displays strict host specificity. 

 In an ancient group of bird parasites like the Mallophaga, where louse 



*Since discovered in Aberdeenshire (Allan 1950) in the nest of the house-martin. 



