|Kurt Plinke, Artist and Naturalist|
Between the Waters
life, Art and The Nature of things on the eastern shore
We have an Aucuba in our back yard, a handsome speckled shrub. Standing about six feet tall, this particular Aucuba, or Spotted Laurel, has begun to encroach upon the path leading to a gated garden. As my wife and I looked at how to cut it back, she noticed a nest in the shrub, about four feet off of the ground. (she always spots that sort of thing before I do)
There were eggs in it, so trimming the shrub was set on hold. I put the loppers away, and we went to examine the nest more closely. I could tell from the shape of the nest that it was made by a house finch. I had seen many of these nests in our yard... the house finch, with it's raspberry-colored head, is one of the more common birds near the house. We peeked into the nest, and saw that there were two pale, almost-white eggs in the nest, and two eggs, dotted with brown flecks. A third pale egg was wedged into a branch just below the nest.
I hate when I see this in a nest. I shouldn't, but I do. I knew right away that one of the Cowbirds we see at the feeders had been there, and had laid several eggs in the House Finch's nest. The Cowbird had also probably pushed the one finch egg out of the nest, as well. I get mad when I see this, because Cowbirds do this to so many native songbirds. There are some species of birds that are seriously parasitized by Cowbirds. That's why I get mad. It doesn't seem fair. On the other hand, Cowbirds are also a native songbird. They even actually have a pretty song, sort of a liquid tumbling song. If they weren't such parasites, they'de be pretty.
Brown-headed Cowbirds, Molothrus ater, are, as I said earlier, native to North America. They frequent open land, and their range has spread from the prairies as we have cleared land and made the eastern United States more open.
Cowbirds are a species of blackbird, relatively small, but stocky, with a large head. The brown-headed Cowbird male is dark, nearly black, with a brownish head and nape. The female is lighter, resembling a large House Sparrow, light tan and brown, sometimes with very pale streaks on the back.
It is the female Cowbird that waits to place her eggs in the nests of other birds. According to the Cornell Lab of Ornithology, All About Birds, (http://www.allaboutbirds.org/guide/brown-headed_cowbird/id), different Cowbird females tend to lay eggs in only one species of bird. Some might chose a Yellow Warbler, while the one in my back yard choses to lay eggs in the nests of House Finches. Not all Cowbirds are so choosy, it appears that a few will lay their eggs in almost any nest.
Sometimes, the female Cowbird pushes the nesting species' eggs out of the nest as she replaces them with her own. Other times, the young cowbird, which hatches quickly, pushes the other eggs out. In either case, the result is that the single remaining young is a Cowbird. The nesting birds feed the young cowbird as though it is their own. The female Cowbird is long-gone, and does not have any association with her young. Seeing small songbird, like a Yellowthroat or Chipping Sparrow raising a baby bird that is twice the size of the "parents" can seem almost comical, even though it is, at the same time, sad.
Some species, such as the Kirkland's Warbler, are so seriously effected by Cowbirds, that they are endangered. Some birds, like the Yellow Warbler, differentiate between the eggs, and build a new nest on top of their old one, trapping the cowbird eggs deep beneath the new nest. Yellow Warbler nests sometimes are a stack of nests, one on top of the other, each containing cowbird eggs that will never hatch.
House finches seem to be among the large group of birds that raise the cowbird young as their own, although I have discovered several cowbird eggs under the finch nest since first finding this particular nesting site. It may be that the female House Finch pushed out the uninvited eggs. According to Cornell, Cowbirds sometimes return to the nest, and finding their eggs gone, destroy the nest altogether.
Despite the risk to the nest by an angry Cowbird, I want to intervene. I want to remove the cowbird eggs myself, helping out the finch family in my yard. So far I am refraining, allowing nature to take it's course. It will be interesting to see what happens.
Kurt Plinke: About Life, Art and the Nature of Things on the Eastern Shore
I write about things I've noticed, places I've been, plans I've made and paintings I've finished or am thinking about.
See recent naturalist observations I have posted on iNaturalist: