Generalist - Specialist

By Dave Hanks

That which makes a species able to survive changing conditions is its ability to adapt. Limiting factors or lack of them is what sets different animals apart. Generalists have fewer limiting factors than specialists. Such is the Coyote who can eat a wide-range diet, and who can live almost anywhere. Not so with Australia’s Koala - who is tied to the eating of Eucalyptus leaves, and is therefore a candidate for extinction. Being a specialist, it has a very narrow range of acceptable living conditions.

A limiting factor can be more than the food required. Nesting needs, such as the Wood Duck needing either tree cavities or nest boxes, or reproductive stimulation that prevents Cheetahs from reproducing in captivity – are both limiting factors. Grizzly bears require large areas that give them isolation, so they are always living on the “edge”.

In the bird world, what generalist is more adaptable than the American Robin? We see them almost everywhere we go and in all seasons of the year. There is little chance of them going extinct.

The Hooded Merganser, a fish eating duck, is a specialist. This small (13 inch) compact duck has a white chest and belly with cinnamon flanks. The chest sports a black stripe and its head has a yellow eye and a crest. The most noticeable trait is this crest, which is white and outlined in black. It is circular in shape, and the duck will either raise or lower it depending on its mood.

It requires fresh water where it feeds on small fish and crayfish. Using its vision, it spots the prey from the water surface. This causes the bird to swim with head submerged and then to dive. A long, thin, serrated bill with a hooked nail on the end allows seizure of the prey underwater.

They are a hard to find bird. Boise’s city park seems to be a dependable place to usually observe this duck. We have also seen them, in winter, at Bosque del Apache Refuge, New Mexico.

(Hooded Merganser with his hood in full display)