Until our recent visit to Reifel Island, I had never seen a cowbird up close. Laurie pointed them out to me, occasionally; little black birds off in the distance, indistinguishable, as far as I could tell, from the starlings.
I had read about them, of course. Cowbirds are those nasty parasites that lay their eggs in other birds' nests, leaving the poor foster parents to do all the work. Worse, the greedy youngsters, hatching first, get all the food and the other occupants of the nest die. That's if the cowbird chick hasn't pushed them out of the nest already.
Just plain bad.
Now that I've seen some, Googled them, and learned a bit more, I've changed my mind about them.
Speaking his mind.
Cowbirds got their name because they hang out around cattle, eating the insects that plague cows and horses; bot flies, horseflies, ticks, etc. If I owned a few cows, I'd want to have a flock of cowbirds on hand.
And their "nasty" trait of letting other birds raise their young? It is suggested that, before the continent was "civilized", when bison roamed the plains and cowbirds took care of them, they stayed with their ranging food source. If they had stopped behind to tend nests, they would have lost contact with the herd and starved. So they laid their eggs and flew away. Today, most of our cattle are confined behind fences, and the need to move on no longer applies, but the pattern is set.
And, so it seems, the harm done to the other birds is not great. Studies show that as few as 3% of the cowbird eggs actually hatch. Most are recognized by the host species, dumped from the nest, broken, or abandoned. Sometimes the chosen foster parents just build another nest on top of the old one containing the cowbird egg.
Many of the foster parents, besides, seem to be stimulated by rearing a cowbird chick and start a new batch of their own; they are often more successful at raising their own families than non-parasitized birds. (See Audubon; Cowbirds and Conservation.)
That's nice to know.
I noticed, going over my photos, that all of the birds are male. The females are a plain grey-brown, and none of my little brown bird photos match the cowbird females.