164 FLEAS, FLUKES AND CUCKOOS 



pass unchanged and unharmed through the ahmentary canal. In this 

 way, the oocysts arc widely dispersed and they are often ingested by a 

 bird which catches and eats the fly. 



Several workers have claimed that the oocysts appear in the faeces 

 of infected birds at definite times of the day, between 3 and 8 p.m. for 

 Isospora and 3 and 9 p.m. for Eimeria. The metabolism of the parasite 

 would therefore appear to be closely Hnked to the host and the 

 voiding of oocysts at definite times may be regulated by the bird's 

 responses to light and dark. 



The genera Eimeria and Isospora present an interesting problem in 

 evolution of host and parasite. Some time in the remote history of 

 birds the ancestors of these Protozoa parted company. It is interesdng 

 to follow their development in tne various orders of birds and to see if 

 other parasites show a similar divergence among the groups in question. 



Order Haemosporidia 



" Of all the human diseases," wrote Chandler in 1946, "there is 

 none which is of more importance in the world to-day than malaria. 

 It has been estimated to be the direct cause of over one-half the entire 

 mortality of the human race." Man, however, is only susceptible to 

 one genus of the family Plasmodidae, while birds fall victim to all 

 three. It is difficult in the present state of our knowledge to estimate 

 the damage inflicted on populations of wild birds by these parasites. 

 Judging from observations made on canaries and other species kept in 

 captivity, and domestic poultry such as ducks and turkeys, the harmful 

 eflfects must be considerable, even if the mortality rate is not high. 



One of the most extraordinary facts in the whole field of bird 

 parasitology is the lack of research into true malaria [Plasmodium) in 

 British wild birds. This seems even more peculiar when it is realised 

 that the transmission of the malaria parasite was first demonstrated by 

 Ross using wild birds in India. The actual species concerned were a 

 crow {Corvus splendens), two pigeons, four larks {Calandrella dukhmen- 

 sis) and six sparrows {Passer domesticus indicus). Moreover, one of 

 the most effective modern therapeutic drugs, paludrine, was discovered 

 in this country; canaries and chickens were used for the experiments 

 concerned. The fact remains that except for a record made over thirty 

 years ago by Coles, we should not know for certain if true malaria existed 

 in British wild birds. It is safe to assume that it is not uncommon, for 

 avian plasmodia undoubtedly occur in every part of the world where 



