12 ITLLINOTS (AUDUBON AB Oia 
Birders & Ecology 
by Donald S. Heintzelman 
Reprinted from New Hampshire Audubon Quarterly 
Few birders think of themselves as ecologists, yet most gradually develop 
an awareness of some basic ecological principles. For example, the im- 
portance of learning the habitat requirements for various species is an 
obvious necessity if one is to locate particular species of birds effectively. 
Obviously, one would not search for a nesting Olive-sided Flycatcher on 
the marshes of New Jersey’s Brigantine National Wildlife Refuge. But 
an excursion to the state’s salt meadows would be appropriate to see 
nesting Laughing Gulls. Of course, most birders with a reasonable amount 
of field experience know the habitat requirements of common species. 
But what about ecological niche requirements? Within a given habitat, 
two species can live together only if they occupy different ecological 
niches. This, stated formally, is the principle of competitive exclusion. 
That is, two species living together do not carry out exactly the same 
activities in exactly the same habitat or direct competition would result, 
and one would be eliminated from that particular niche or habitat. 
How, then, can a knowledge of niche requirements aid a birder in 
deriving more enjoyment from his hobby? One way is by allowing him 
to understand better the workings of food chains and food webs. Let’s 
consider some examples, using first the foraging ranges of wood warblers 
(Parulidae). Not all warblers seek food in the same locations within 
their required breeding habitats. Some search for food close to the ground, 
others at medium heights and still others at the top of tall vegetation. In 
other words, the ecological niches of the various species are distributed 
in layers, or stratified, according to the various heights which vegetation 
attains. Examples of warblers with foraging ranges confined to the lower 
vegetative strata are: Canada, Kentucky, Prairie and Worm-eating. Spe- 
cies with medium foraging ranges include Black-and-White, Black- 
throated Blue, Golden-winged, Blue-winged and Magnolia. Some high 
foraging species are Blackburnian and Cerulean. However, not all war- 
blers are rigidly restricted to specific strata in conducting their foraging 
activities. Chestnut-sided and Hooded Warblers, for example, range from 
low to medium levels; but Nashville and Yelow Warblers move from 
