Keeping the backyard bird feeders full is a relatively easy but endless task. Today’s ravenous flock of big black birds was making sure that the task was repeated frequently. They were gobbling down all manner of seeds, both from the feeder perches and the ground. They were keeping the usual assortment of songbirds away, making their gluttonous behavior all the more challenging.

The spotting scope was already set up overlooking the backyard. It took me just a few seconds to pull one of the aggressive birds into view. A defiant yellow eye, boldly set in an iridescent purple-blue head, stared back at me. The rest of the body was glossy as well, but in different tones of purple and blue-green.

The common grackle (Quiscalus quiscula) is a widespread, common bird in the Eastern United States. Bigger than most other blackbirds, it stretches to about 12 inches from its long, tapered tail to its bill. The black beak is prominent, more long than heavy. Grackles stand on tall, stout black legs.

They prefer to forage on the ground but they will perch precariously if necessary to reach food.

The diet of the common grackle centers on grain, especially corn. Common grackles will descend upon a corn field from the moment it’s planted until it’s harvested. Walking boldly behind planting equipment, they peck at newly sown seeds or unearthed grubs. As the corn begins to tassel, they tear at maturing ears to eat growing cobs. After the harvest, they descend like a dark cloud, eating any remaining kernels. Common grackles do millions of dollars of damage annually.

The backyard grackles I was watching weren’t nearly so destructive, although they were going through the seed at a distressing speed.

Though they prefer grains, grackles readily eat thistle, suet or sunflower seeds. If those foods are not available, grackles will eat just about anything else at hand, including insects, frogs, mice, worms, other birds and even fish. (Grackles wade into shallow water to nab schooling minnows.) Discarded garbage is another food source for these omnivores.

The common grackle is a bird of the United States, with essentially all of the species spending most of their days spread across the Mississippi River Valley to the Atlantic Ocean. They are year-round residents. About 10 percent of the population, primarily from the Midwest, do venture into central Canada in the summer to breed but return to the United States in the fall.

Common grackles display an odd geographic variation in color. Those south and east of the Appalachian Mountains have an iridescent purple-blue head, purple belly, and blue-green tail. Those north and west of the Eastern continental divide have blue-green heads and brassy bronze bodies. From afar, all of the birds look black, but at closer distances the iridescent head is easily distinguished from the glossy body. Of course, there are exceptions, but generally the grackles in the Chesapeake watershed have purple-blue heads.

Aside from the iridescence, the most noticeable characteristic of the common grackle is its tail. In flight, the bird often holds its tail feathers in a shallow vee, giving the tail a
keel shape.

Grackles are noisy birds. They like to perch high in the treetops, surveying the land below and loudly calling. Both males and females sing, and all engage in raucous chattering in flocks. The loud, squeaky CHAA or readle-eak is the opposite of the dulcet songs of the goldfinches that typically fill our backyard.

Common grackles can be found in almost any habitat except dense forests. They are equally comfortable in salt marshes, urban parks and virtually everywhere in-between. They are also social birds, especially in the winter when they gather in huge gangs with other blackbirds like starlings and red-winged blackbirds. The flocks can easily number in the tens of thousands.

Avaricious, sometimes destructive, pushy and able to make themselves at home in almost any habitat: It’s hard not to view these U.S. birds as the living manifestation of some of nation’s worst traits.

And yet the birds are not thriving.

Common grackles are in serious decline. Although they seem to be expanding farther westward and they are still abundant, the population has fallen nearly 60 percent since 1966, according to the authoritative Breeding Bird Survey. Ornithologists are thus far stumped about why the bird’s abundance has fallen so significantly.

I wonder, is this decline also a reflection of the United States? While our human population continues to grow, I sense a disturbing decline at home. With a rise in hate crimes and crude behavior, proposed massive cuts to environmental programs, attacks on healthcare — zero budget for the Bay Program! Our worst instincts seem to be increasingly manifest.

Unlike the case of common grackles, I don’t think it is puzzling to understand why.