With the help of several Cville Buzz readers, the mystery has been solved. The unidentified birds in my yard have been identified. The two, stocky gray birds I could not find in my bird books are juvenile Brown-headed Cowbirds. The reason they were so hard to identify is that they were young birds and looked nothing like their parents pictured in books.
I had a feeling they were juveniles because they weren’t particularly concerned about the presence of humans and they often fluttered their wings as if they wanted to be fed, as most young birds do. And it all makes perfect sense.
Cowbirds are brood parasites. They do not build nests of their own, ever, but lay their eggs in the nests of other birds. Over 200 different species of birds are known to raise cowbird chicks in their own nests, often at the expense of their own young. I have heard that robins can smell a rat when they see one and will not hatch the eggs. Yellow warblers are also able to identify the counterfeit eggs, but are too small to move them, so they rebuild over the cowbird eggs. My hunch is that a family of house finches raised these two strangers because when the young cowbirds saw the finches at the feeder, they immediately began fluttering their wings.
The cowbird hen’s timing must be exact, it seems, to lay an egg or two when the natural parent is away, so the window of opportunity is small.
The adult cowbirds are rather homely, sort of a poo-poo brown and the male and female are not monogamous. They split after fertilization of the eggs and go their separate ways while the hen prowls around looking for potential nests.
Cowbirds often flock with other blackbirds, like starlings and grackles, and Lord knows we had plenty of those this year.
Interestingly, cowbird eggs hatch sooner than do other species, giving the free loaders a head start at the expense of other chicks. I consider these bums nuisance birds and they are not welcome in my yard.
But at least I now know what they are, and they are pests.