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. 
Fic. 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 
