The little scavengers were scattered about, hopping from a bread crumb to a piece of discarded paper and then flitting off a few feet away. The constant movement was punctuated with a monotonous refrain of "cheep."

The birding was less than ideal, but then again, we were at a food court inside an airport. This wouldn't be mistaken for prime birding habitat. Yet the birds were there and not looking a bit out of place.

The sparrows were about 5.5 to 6.5 inches long with heavy bills. The females were a muted mix of browns and blacks, with a liberal dose of gray and a bit of rusty brown. They have a poorly defined eye stripe, and their bills were a dull yellow. The males worked from the same palette, but the result was much more richly rendered.

A male who was picking away at a crumb from a hamburger bun had a gray cap with a bold black throat patch and contrasting white cheeks. His black mask extended outward from his black, conical bill. A reddish-brown streak extended from behind his eye and grew into a nape of the same color. His wings were a mixed pattern of black, brown, gray, russet and white. The breast and belly were white. In every particular, the colors on the male were brighter than the corresponding ones on the female.

House sparrows (Passer domesticus) are ubiquitous birds in the lower 48 United States. The birds can be found everywhere in the Western Hemisphere except Alaska and northernmost Canada or the Andes and Amazon basin. Travelers can spot house sparrows at every temperate location, from Toronto to Tierra del Fuego.

The extraordinary range of the birds in the Western Hemisphere is all the more remarkable because the birds were unknown here just a century and a half ago.

It was a different world in the 1850s. Every educated person could be expected to recite long passages from the classics and the Bible. Traveling theatrical troupes were popular. One avid fan decided to introduce into North America every species of bird mentioned in Shakespeare's plays. Thus, the lowly sparrow was transported across the Atlantic and released in New York City's Central Park in 1851. Although minor introductions followed, the vast majority of house sparrows in the Americas descended from those Central Park birds.

House sparrows are native to Eurasia and northern Africa. Because of introductions and their affinity for humans, the birds now exist on every continent except Antarctica.

These Old World sparrows live where people live; and we live nearly everywhere. They are more likely to be seen flying out from behind a store's sign than in a forest. They seem to prefer artificial nest sites like traffic lights and building overhangs. If twigs aren't available for nest building, a discarded piece of string and strip of plastic will suffice.

It takes only a month from the laying of the eggs to fledging, facilitating multiple broods of four to five birds annually.

Although they are everywhere, house sparrows are not among the species most people can recognize. The birds lack the arresting color of a blue jay or cardinal, and they don't have the pleasing song of a springtime robin.

Pigeons, with their dominant size, demand recognition. Sparrows are more plentiful, but they weigh just an ounce. They are easy to overlook.

Many birders dislike house sparrows because they displace native species. They defend their nest aggressively and are equally assertive in competing for food. House sparrows aren't picky about their diet, eating both seeds and insects. And, as was evident as I looked on, they were also willing to gobble down the stray french fry or burger bun.

A bird that will eat a varied diet and isn't choosy about shelter is well-suited for adaptation. Functional flexibility and rapid reproduction rates have accelerated its evolutionary development. In just 150 years, distinct subpopulations have evolved. The birds of the cool, rainy Pacific Northwest are plump and dark. Their counterparts in the desert Southwest are slimmer and more sandy-colored.

Not surprisingly, house sparrows are a favorite with researchers. More than 5,000 studies have used these hardy, abundant birds as subjects.

Here at the airport food court, people were midway through their personal journeys. Their final destination may have been a distant continent or a subdivision nestled somewhere in Chesapeake country. Either way, house sparrows almost assuredly awaited them.

The house sparrows go where they can and make whatever life they can manage. In this, they seem very much like humans, always expanding their range and always aggressively seeking whatever resources they can consume or otherwise use. The birds are simply following biological imperatives.

I looked around at my fellow travelers and wondered, are we ultimately that different?