Sparrows with Racing Stripes

COURTESY WOLFGANG WANDER
A few days ago, a fellow birdwatcher mentioned he had seen his first white-throated sparrow of the season. He is a recent transplant from Connecticut where, in theory, Zonotrichia albicollis is a year-round resident, as it is here in central New Hampshire. That is, one would think he would be used to seeing them during the breeding season as well. I made some remark to that effect, and he said, “Oh, I guess they just came down the mountain.” Exactly so.

He lives in what is fondly referred to as “the flat” (Cornish has one too) at an elevation just under 720 feet above sea level. I live up the hill in “the center,” which is about 200 feet higher in elevation. I don’t hear or see white-throated sparrows during the summer either. Unless I take the dog for a walk at Langenau Forest, which is between 1,400 and 1,600 feet of elevation. There I find Z. albicollis all summer long.

It was likely so down in Connecticut as well, as this species prefers an ecosystem dominated by spruce with northern hardwoods mixed in. That assemblage is found at progressively higher elevations as one goes southward. In the Appalachians it has been measured to occur 100 meters higher with each degree traveled south. Wilmot is ~1.5°N of Connecticut, so my colleague would have to do some hill-climbing to see the species in the Berkshires.

I do like the reappearance of white-throats in my yard, in part because they are boldly marked and, as one observer remarked, a lesson in the basic parts of a passerine songbird. The white throats of the adults are outlined with a black malar stripe. Their lores are marked with a yellow spot, behind which extends a broad white supercilium. The crown is black with another white stripe extending from the bill to the nape. The nape itself is gray, finely striped with brown.

Although Z. albicollis is a larger(~6.75 inches) than average sparrow, it is the smallest of the four members of this genus. Only two species occur regularly in the East; the other is the white-crowned sparrow (Z. leucophrys). I told my fellow enthusiast I always look for a few white-crowns in flocks of migrating white-throats. His early September white-throat had probably come “down the mountain,” but this sparrow ranges to northern Quebec in eastern North America and retreats to as far south as northern Florida in the winter.

In contrast, the white-crowned sparrow breeds only as far south as northern Quebec in the East and winters north only to southern Pennsylvania. In other words, we see them only in migration; there isn’t enough altitude to climb around here to satisfy their ecology. Whereas, the white-throat is described as a habitat generalist, the white-crown’s habitat preferences are quite specific: “Necessary habitat features of breeding territories include grass, either pure or mixed with other plants; bare ground for foraging; dense shrubs or small conifers thick enough to provide a roost and conceal a nest; standing or running water on or near territory; and tall coniferous trees, generally on [the] periphery of territory” (DeWolfe and Dewolfe, 1962 cited at birdsoftheworld.org).

Both species are said to benefit from logging operations and other disturbances because neither like an extensive closed canopy, preferring the edge habitat and dense regrowth created by cutting and recovery from harvesting. Cattle grazing along riparian habitat in the western mountains, however, has an adverse effect.

Z. leucophrys is only a quarter inch longer than its cousin but has a slimmer build that gives it a different overall appearance. While both species have the “racing stripes” from front to back on their crowns, the throats of Z. leucophrys are a clean light gray. This species also has the tendency to occasionally raise the feathers on its crown, giving the head a high-domed look that the white-throat does not sport. The subspecies that we see in the East also has a pink bill that distinguishes it from the white-throat, which has a larger, gray bill.

According to The Birds of New Hampshire, the earliest fall arrivals of white-crowns are in the second or third week of September with peak fall migration in the first three weeks of October. It is rarely seen in large numbers; no single-day counts greater than 60 have been recorded since 2000. When I have looked for them among flocks of white-throats, I have found only one or two.

Identification is complicated by the juveniles and the rare presence of western subspecies. Aside from the obvious presence of a white throat, the adult Z. albicollis can be distinguished by its yellow lores. In eastern taiga Z. leucophrys the lores are black and in the western taiga subspecies they are white. First-winter white-throats have dirty looking throats and a smudgy black line extending down from the bill on either side. First-winter white-crowns have alternating gray and brown stripes on the head, very different from the adults of either species. First-winter white-throat stripes are less bright than those of the adults.

While the white striping of adult white-throats can vary widely between tan and bright white, that of adult white-crowns shows no such variation. While plumage variations in Z. leucophrys are geographic, the tan-striped morphotype of Z. albicollis is a stable genetic alternate within the whole population. Most tan-striped individuals breed with white-striped birds, which keeps the balance of the morphotypes stable. Genetic studies show that this chromosomal inversion is older than the species. That is, it is an ancestral trait that has persisted in Z. albicollis, but not in the other members of the genus.

Although white-throats are genetically more interesting, white-crowns have the frisson of rarity. I will be searching through every flock I see.

Bill Chaisson has been a birdwatcher for 50 years. He lives and works in Wilmot. A collection of these essays, Of a Feather, is available at amazon.com