ALWAYS IN SEASON: Cowbirds head the avian enemies list in North America

The brown-headed cowbird is probably the most reviled bird in North America, coming in ahead of immigrants such as the house sparrow, European starling and rock dove (aka pigeon).

Of course, revulsion is a matter of circumstance. On a golf course, the Canada goose is reviled, because it doesn't clean up after itself. In a sunflower field, the red-winged blackbird would be reviled, because it eats sunflower seeds.

For bird lovers, though, pride of place on the avian enemies list definitely falls to the cowbird. That's because the cowbird is what people who study birds -- ornithologists -- call "a brood parasite." It lays its eggs in the nests of other birds.

The cowbird is the only brood parasite among American birds. For this reason alone, the cowbird is worth knowing.

Cowbirds are fairly common in our area. At this time of year, cowbirds don't have anything to do but eat and loaf, and so they are quite easily found. Often they pick up insects where grass is short, such as lawns and pastures.

Hurry, though, because cowbirds don't spend much time here. They don't have to, since they don't establish breeding territories or build nests or tend their own young. All of that falls to other species.

So, the cowbird is peripatetic, appearing here with the return of native nesters and then moving on. Some cowbirds will stick around awhile, as long as food is abundant, but the bulk of the population wanders around after its eggs are laid.

In general, I don't expect to see cowbirds after the end of July. Until then, I'll probably encounter them pretty much daily.

The cowbird is easily recognized. It is a black bird with a brown head. Males show some iridescence, especially early in the season, when they are busy attracting females.

As with other members of the blackbird family, female cowbirds are duller than their mates, but this difference is less among cowbirds than among other blackbirds.

There are two species with which the cowbird might be confused. The first is the common grackle, which is much larger and more iridescent. It used to be called "purple grackle."

Grackles also have longer tails and are given to prancing about rather regally. This drives some homeowners bonkers, since grackles are aggressive birds that don't hesitate to take eggs or young from the nests of other species.

They do tend their own young, however.

The second, more difficult identification problem is Brewer's blackbird, which is pretty much the same size as the cowbird. Again, it is more uniformly colored, however, and shows a bright yellow eye.

Of course, all of this is difficult to see, so it's best to have a second look to clinch the identification.

You're more likely to see a cowbird around here than a Brewer's blackbird. Brewer's does nest here, but it is much more common in migration, especially in the fall, when quite large flocks are possible.

Other members of the blackbird clan shouldn't present identification problems. The red-winged, yellow-headed and rusty blackbirds pretty much live up to the billing in their names.

Interestingly, three of the most reviled species are members of the blackbird family. Partly, this is because of their abundance. Red-winged blackbirds may be the most numerous birds on the continent.

Cowbirds now have a continent-wide distribution, but this is a product of historic times rather than natural conditions. Before European settlement, cowbirds were limited to the Great Plains, where they followed the herds of buffalo, picking up insects that the great beasts stirred up.

Their habit of brood parasitism enabled them to move about, pretty much without responsibility, and this remains a feature of the species.

Now they have more places to move.

Although people tend to think of the Plains as virtually treeless, this has never been the case. Trees occurred along prairie lakes and rivers, and in much of the central and western parts of North Dakota, there were copses of poplar trees.

And pretty much everywhere, there were stands of buck brush and wolf willow.

In other words, the Great Plains in a state of nature were a mixed habitat -- exactly what the cowbird prefers and exactly what European settlers created when they began to clear forests to establish fields, farms and small towns.

Cowbirds moved into these clearings.

Cowbirds are destructive. Their eggs are larger and their young more aggressive than those of most host species, and so their victims rear cowbird chicks rather than their own.

Jacobs is publisher of the Herald. Reach him at (701) 780-1103; (800) 477-6572, ext. 1103; or send e-mail to mjacobs@gfherald.com .