The one with the pin spot

By BILL CHAISSON
Of a Feather
As I write on Friday morning, Thursday’s cold snap has now been followed by a warming trend that may bring rain. It has been that kind of a winter: mild, but a bit messy because of the constant down and up from freezing to thawing. It may just be a coincidence, but I wonder if it is causing the birds to stay in the woods and fields to forage rather than come to my feeders.

It has been very much a “usual suspects” kind of winter so far. The black-capped chickadee was first species to show up; they appeared less than an hour after I put up the feeders. Then the juncos and the blue jays arrived, and for a few weeks in December these were the stand-bys. There were repeated visits from a couple of downy woodpeckers and a titmouse or two, and occasionally the starlings that roost in the tower of the old town hall across the road will sweep in and stalk around in their wind-up toy kind of way.

In early December a couple of blackbirds stopped by. I was initially excited, hoping they were rusty blackbirds, a relatively uncommon species, but they turned out to be immature red-wings, lingering up north before perhaps spending the duration of the winter all the coast of southern New England.

We have received one or two visits from a white-breasted nuthatch, but I have now not seen one for weeks.

In late December, I finally saw the little gray, brown and red sparrows with the pin spot on their chests. The tree sparrows (Spizelloides arborea) had arrived. Called “winter chippies” for their resemblance to the chipping sparrow (Spizella passerina), the tree sparrows breed in the northern half of the taiga and into the southern edge of the tundra. This resemblance has proved to be an example of convergent evolution; the two sparrows are not closely related, although for many years they had been classified in the same genus (Spizella).

David Slager and John Klicka of the University of Washington recently – in 2014 — proposed the genus Spizelloides (which roughly translates as “resembling Spizella”) for the tree sparrow on the strength of several molecular genetic studies that have shown that S. arborea is more closely related to juncos and the fox sparrow than to the rest of the spizellids. In the language of evolutionary systematics the genus Spizella has been found to be “polyphyletic”; it had more than one trunk before it branched into several species. Evolutionary theory insists that taxonomic names reflect relatedness (not resemblance), the job of systematists is to find polyphyletic groups and rename them to make them monophyletic.

The tree sparrow is actually a good inch longer than a chipping sparrow, but you never see them together, so it is difficult to use size to distinguish them. Both species have rufous caps on their crowns. Both have two white wing bars and striped backs. After that their appearances begin to diverge. While both have lines through their eyes, that of the tree sparrow is rufous red, while that of the chipping sparrow is black. In the tree sparrow the superciliary area (above the eye) and auricular area (cheeks) below the eye line are gray, while in the breeding plumage of the chipping sparrow the superciliary area is bright white.

Two winters ago, while I was living outside Saranac Lake in the Adirondacks, I had a strange sparrow visit my feeder for several weeks. I eventually realized it was a chipping sparrow. I didn’t recognize it because (1) as a migratory species it really should not have been in upstate New York in the winter, and (2) I had never seen a chipping sparrow in non-breeding plumage. The bright white superciliary area was a dirty white or gray like the tree sparrow rather than the bright white breeding garb. Consequently, for several days I starred at this sparrow and wondered, “What is this funny looking tree sparrow without a pin spot?”

The so-called pin spot is a feature common to sparrow species in many different genera. Its widespread appearance suggests it was present in some distant ancestral species that formed the root of the family Passerellidae (the New World sparrows). The familiar song sparrow (Melospiza melodia) has a pin spot that is set amid vertical bars on the chest. So does the fox sparrow (Passerella iliaca), the closest relative of the tree sparrow, according to molecular genetic studies.

What is even more fascinating is that in some species the pin spot is present in the juvenile plumage, but not in the adult. Two species present in this region, the swamp sparrow (Melospiza georgiana) and the white throated sparrow (Zonotrichia albicollis), are examples. This suggests that the pin spot could be an example of neoteny, a juvenile characteristic that persists into adulthood. A familiar example of neoteny is our own relatively flat faces and high foreheads, which are a juvenile characteristic in other apes but persist into adulthood in our species.

In any case, the winter chippies are now regular visitors to my feeders. Happily, they seem less intimidated by my numerous blue jays than their cousins the juncos. Recently I have seen two goldfinches at my nyger seeds, but they are terrified of the jays.