144 The Bird 



there is such specialization for feeding on particular 

 varieties or portions of plants. We find fruit- and grain- 

 eaters, besides those which feed almost entirely on buds, 

 leaves, berries and nuts, nectar, sap, and even pollen. 

 Lichens form a considerable item in the bill of fare of 

 ptarmigans, the Arctic grouse. We have even dedicated 

 certain plants to birds which show a decided partiality 

 for them, duckweed and partridge-berry. 



FIG. 109. Vireo, an insect-hunter, with a delicate, hooked bill. 



There is no doubt that a great many plants benefit 

 from the cross-fertilization of their flowers by humming- 

 birds carrying the pollen from blossom to blossom. Of 

 one of the sugar-birds of South Africa it is said: "When 

 sucking up the nectar of one of the larger protea-blossoms, 

 the bird perches on the edge of the flower, plunges its 

 long bill and the greater part of its head downwards 

 among the petals, and retains it in this position until 



