FOOD AND ITS UTILISATION 89 



trees. One may almost say that there is no end to the 

 diversity of ways in which birds deal with insects. 



in. Mixed Feeders.— Many birds enjoy both vegetarian 

 and carnivorous diet. The thrush has its fruit and its 

 snails ; ducks eat a lot of duck-weed but they are ready for 

 all sorts of small aquatic creatures ; the Carrion-Hawks of 

 South America devour carrion, sickly lambs, the snakes 

 roasted in a veldt fire, and vegetable food. The last is 

 an extreme case, but it must be said of many birds that they 

 are not fastidious. Often they will feed on insects during 

 one season and on vegetable materials during another. Of 

 special interest are those cases where the young are fed on 

 a kind of food different from that on which the adults mainly 

 depend. Thus the young rooks are fed for a while on 

 insects only and the same is true of young sparrov^s. 



IV. Oddities of Diet. — The Kea Parrot {Nestor notahilis) 

 of New Zealand, though belonging to a race habitually 

 vegetarian or frugivorous, has taken to killing sheep, and 

 does very serious damage in certain places. It alights on 

 the sheep above the loins, tears aside the fleece, and cuts 

 open the skin with its strong bill, and devours the fat and 

 flesh near the kidneys. To account for this remarkable 

 change of habit, it has been suggested that the bird began 

 by pecking at the fat adherent to the sheep-skins hung up 

 to dry. It is said to enjoy its mutton-chop at the Zoo. 



These changes of diet are of much interest both theoreti- 

 cally and practically. They illustrate variations in habit, 

 tentative answers-back in the struggle for existence. The 

 herring-gull is normally a fish-eater, but in the last quarter 

 of a century in the North of Scotland it has become in- 

 creasingly vegetarian, frequenting the farmer's fields and 

 devouring turnips, potatoes, and the ears of corn from 

 the stooks. During the summer the Black-headed Gull is 

 very largely insectivorous, and Mr. Beebe notes that on the 

 pampas near Buenos Ayres the people look for the flocks 

 of gulls as the only relief from the hordes of grasshoppers. 

 A woodpecker, as Selous notes, may occasionally function 

 as an ant-eater. 



