24 FLEAS, FLUKES AND CUCKOOS 



occasion. For all we know the species referred to by Herodotus as the 

 " Trochilus " may now be extinct. However, it is generally believed 

 that the Egyptian plover [Pluvianus aegyptius) is the species concerned 

 and it is to-day referred to as the crocodile-bird. It certainly pos- 

 sesses many of the attributes generally associated with birds mani- 

 festing this type of symbiotic behaviour. Its plumage is conspicuous, it 

 is unusually tame and according to at least one observer its flesh is 

 extremely unpalatable. All birds which habitually "de-louse" large 

 animals show a certain degree of tameness and boldness. This is 

 equally true of starlings, ox-peckers, phalaropes, mynahs, weavers and 

 magpies in the old world and grackles, tickbirds and cowbirds in 

 America. Moreover, the majority of birds which "de-louse" cattle or 

 associate with them on pastures are gregarious and go about in flocks or 

 small parties. One is inclined to think that only species which are in 

 some way protected against predators can afford to expose themselves 

 continuously and blatantly in the middle of open country on the backs 

 of cows or buffaloes. The flock definitely affords them some protection, 

 for birds of prey will often attack certain species if they happen to come 

 across a single individual but would not dare to do so if they are present 

 in numbers. Cott's recent work on the unpalatability of certain birds 

 suggests that the "de-lousers" are evil-tasting species which conse- 

 quently do not fear raptorials. 



The buff-backed heron is a scarce wanderer in Britain, only two 

 specimens having been recorded with certainty from this country. In 

 its native haunts in southern Europe, Asia and Africa it is known as 

 the cattle-egret. This bird has developed a close relationship with 

 cattle, with which it associates in the fields, feeding on the ecto- 

 parasites which drop off them and the insects which the animals disturb 

 in the grass as they wander through the pastures. One of the most 

 interesting points about this partnership is the egret's predilection for 

 domestic animals and the way in which it has modified its habits to fit 

 in with theirs. In Africa in certain districts during the rainy season, the 

 cattle are concentrated in fly-free areas north of latitude lo and the 

 buff-backed heron moves up with them. In the dry season large 

 numbers of both animals again move southwards — the birds' local 

 migration being entirely dependent upon the cattle. At sunset the 

 domestic animals are confined in a compound and the egrets then 

 repair in a flock to a nearby swamp or lake. After drinking and bathing 

 they return to the village or cattle camp where they roost communally 



