It’s that time of year again.
The inquiries used to come by telephone, but now they pour in by e-mail, twitter, and facebook: What’s this sparrow in my yard?
And why is it begging from the Song Sparrow / Northern Cardinal / Yellow Warbler … ?
Brown-headed Cowbirds are among my very favorites, with a fascinating breeding strategy evolved over the millennia in parallel with their foster species. Because they stay with the adoptive parents for some time after hatching, the juveniles can be confusing to their human watchers. With a couple of centuries’ experience behind us — collectively, I mean — we know to look for the mid-length blackish tail, the very stout dark tarsus and toes, and the square head with its large eye and short, conical bill.
It wasn’t always so easy, though, and inevitably, the young Brown-headed Cowbird was once described as a new species, the Ambiguous Sparrow, by none other than Thomas Nuttall himself:
Of this very distinct, and plain, mouse-colored Sparrow, I, at present  know scarcely any thing, excepting that it was shot in this vicinity (Cambridge [Massachusetts]) in the early part of the summer of 1830. The specimen is in fresh plumage; and in its general color, both above and below, with the very unusual length and pointedness of the wings, and the distinct graduation of the feathers, it might, without looking at the bill, be at once taken almost for the common Pewee [= Eastern Phoebe, similarly plain grayish].
In 1839, Peabody still listed the Ambiguous Sparrow among the birds of Massachusetts; at that point, there was still only a single specimen known, and Peabody cites approvingly Audubon’s suggestion that the bird might in fact be the “winter plumage” of the White-crowned Sparrow.
Audubon soon bethought himself and rejected what Coues, always eager to call a spade a shovel, dismissed as his “hasty surmise.”
In describing his plate of the Brown-headed Cowbird, the American Woodsman wrote
The young bird from which I made the present figure  was sent to me by my friend THOMAS NUTTALL, Esq., through Dr. TRUDEAU. It is the same as that described by the former gentleman under the name of “Ambiguous Sparrow, Fringilla ambigua,” at p. 485 of his Manual of the Ornithology of the United States and of Canada. On inspecting it, however, I at once felt convinced that it was nothing else than a young Cow-pen-bird, scarcely fledged, it having been found “in the early part of the summer of 1830.” With the view, therefore, of preventing further mistakes I thought it well to figure it.
Audubon’s hopes “of preventing further mistakes” have gone unfulfilled, and this will continue to be one of the most frequently misidentified birds in North America; but at least now we know that we’re in good company when we find ourselves feeling a little unsure about that ambiguous “sparrow” in the backyard.