SYMBIOSIS 21 



there is considerable difference in the advantages which accrue to a 

 sacred cow of the tlindus and a British dual-purpose shorthorn. 



A bird which may, with justification, be considered a symbiotic 

 partner of man is the barn-owl (Plate VI). It regularly makes use of 

 sheds, out-houses and barns during the breeding season and also 

 frequently roosts in buildings. In return it renders an invaluable 

 service by destroying large numbers of vermin which infest stacks and 

 farmyards. " It is as useful in clearing these places from mice," 

 remarked Pennant, "as the congenial cat." 



There is one family of birds, the starlings (Sturnidae), of which 

 several species have, independently in different parts of the world, 

 developed symbiotic relationships with the large grass-eating mammals. 

 The common starling in Britain supplements its diet by paying periodi- 

 cal visits to flocks of grazing sheep and cows and feeding upon the 

 insects which they stir up in the grass, or by actually picking parasites 

 off the animals' backs. 



There are few prettier sights than a flock of starlings whirling out of 

 the frosty air — their wings transparent against a low winter sun — and 

 setthng among folded sheep, or a herd of cows. They work carefully 

 and painstakingly over the ground which has been disturbed by the 

 footsteps of the farm animals, and perform an extremely useful service 

 by destroying the disease-carrying ecto-parasitesofdomestic animals and 

 removing grass-eating insects and parasitic worms from their pastures. 

 The relationship is certainly of mutual benefit, but although quite 

 regular, it is essentially casual and each party can do quite well with- 

 out the other. The African ox-peckers [Buphagus], on the other hand, 

 obtain their entire food supply and much of their nesting material from 

 the bodies of the large herbivores and are thus wholly dependent on 

 wild and domestic animals. They have developed a very close relation- 

 ship with their partners, especially the rhinoceros, for which animal in 

 particular they act as sentinel. Big game hunters were the first to 

 appreciate this fact, for the birds frequently spoiled their chances 

 of a fine bag. "On many occasions," wrote Andersson, "has this 

 watchful bird prevented me getting a good shot at that beast ; the 

 moment it suspects danger it flies up into the air uttering sharp 

 shrill notes that never fail to attract the attention of the rhino- 

 ceros, which, without waiting to ascertain the cause, almost instantly 

 seeks safety in precipitate flight." Moreau has noted that the ox- 

 peckers, on occasions, stick very close to their "hosts", even clinging to 



