ILLINOIS A UID Wb O NSB Url LrE! THAN 13 
medium to low ranges. And the Blackthroated Green Warbler ranges 
from medium to high levels in its food gathering efforts. The Cape May 
Warbler sometimes ranges from high to medium levels. 
Other factors which also permit utilization of different ecological 
niches are differences in a species anatomy or morphology. Among herons 
and egrets, for example, the Great Blue Heron is able to exploit food 
sources in deep water because of its long legs. Common Egrets would 
seek food in shallower water, and Black-crowned Night Herons would 
confine their feeding efforts to the shallowest water of all. Hence, in these 
examples, the physical size of the various species determines more or less 
where each can feed. 
Similarly, on the Serengeti Plain in Tanzania as many as six species 
of vultures may feed upon a carcass. Although there seems to be chaos 
rather than organization as the birds attempt to feed, each species oc- 
cupies a somewhat different ecological niche in terms of its food require- 
ments and related physical adaptations for food gathering. For example, 
the largest species — Lappet-faced Vultures and White-headed Vultures 
— break open the skin of a dead animal and feed upon skin, sinew and 
flesh adhering to bones. In contrast, Ruppells Griffon Vultures and 
White-backed Vultures have unusually long necks which enable them to 
reach inside a carcass to eat soft internal organs. Additional anatomical 
adaptations further aid them in exploiting this niche. Finally, Hooded and 
Egyptian Vultures are smaller birds with slender beaks. They fed upon 
scraps of flesh clinging to bones or scattered on the ground near a carcass 
after the larger vultures and other scavengers have eaten. Additionally, 
some individual Egyptian Vultures have learned to use stones as tools 
by lifting them in their beaks and flinging them at Ostrich eggs. After the 
shell is broken, the vulture eats the contents of the egg, thus exploiting 
still another food source not normally vulnerable to other birds. (This 
extraordinary stone throwing. behavior of some Egyptian Vultures is an 
example of true tool use by an animal other than man.) 
The woodpeckers (Picidae) of North America have evolved into 
two branches, each leading to increased specialization. The unspecialized 
flickers (Colaptes) form the base from which the two woodpecker 
branches are derived. On one side, the Pileated Woodpecker remains rela- 
tively primitive and more or less resorts to behavior and ecological niche 
afhnities similar to flickers. But at the apex of this branch appears the 
rigidly specialized Ivory-billed Woodpecker whose niche requirements 
are so specific that the species has become nearly extinct due to loss of 
most of its required habitat (alternative habitats do not meet its niche 
requirements ). 
