Wild Side: White-throated sparrows

Catch them in snowy thickets during Vineyard winters.

0
The white-throated sparrow can be found in thickets and edge habitats throughout the Island. — Matt Pelikan

An endless source of mirth among birders is the way common names for birds often ignore obvious traits and focus instead on obscure markings. The eponymous tinted tummy on a red-bellied woodpecker, for example, is present only on males and, even on them, is subtle and rarely visible under field conditions.

Refreshingly, the white-throated sparrow lives up to its billing. The pattern of a pale throat outlined by dark “whisker” markings is virtually a characteristic of sparrows as a group. But on a well-marked white-throated sparrow, the pale throat shines like a beacon, contrasting strongly with a dusky gray face and breast.

A common migrant and wintering species on Martha’s Vineyard, Zonotrichia albicollis, can be found in thickets and edge habitat across the Island. The species does not breed here, and while it can be hard to tell lingering winter residents from spring transients, it’s presumed that relatively few pass across the Island in spring. But beginning in early October, white-thoated sparrows begin to filter in, eventually reaching respectable levels of abundance that persist through the winter. Soo Whiting’s “Vineyard Birds II” reminds me of a notable tally of 890 on the 2003 Christmas Bird Count.

While these birds manage just fine in natural settings, they also appear tolerant of human activity and fond of the habitat created by typical landscape plantings. The species is among the birds most commonly observed at feeding stations, where it forages, often in small flocks, almost exclusively on the ground. When not scrounging seeds, this bird disappears into dense shrubs or brush piles, where its streaky brown plumage renders it nearly invisible.

Even while hidden, this species is talkative. It gives two distinctive call notes: one a loud, metallic “chink,” the other a thin, high-pitched “tseep.” And its song, given by transients in spring as well as on the breeding grounds, is glorious — a clear, whistled tune often rendered as “Oh, Canada, Canada!”

No one is likely to accuse any sparrow of excessively bright coloration, but the white-throated sparrow sports a few  details that lend it some visual zing. In front of each eye is a spot of yellow, which can be quite intense and offers a useful field mark. And on some individuals, the crown is boldly striped in black and white, creating the possibility of confusion with the closely related (and also aptly named) white-crowned sparrow.

On other white-throats, the head pattern is much less bold, with the white crown stripes more like a muted brown. Males tend to show somewhat more intense coloration than females, but the variation in head color turns out not to be determined by sex. There are, in short, two distinct color morphs of white-throated sparrow, exhibited by both sexes and with the differences determined genetically and persisting through the life of an individual bird.

This breakdown of a species into two distinctive forms is odd among songbirds and has, accordingly, caught the attention of many researchers. In what I can only describe as a truly bizarre bit of avian biology, these morphs turn out to be associated with significant behavioral differences, and coloration plays a major role in mate selection in this species. I haven’t room here to summarize all this, but if you’re interested, you can read a terrific account by my friend Kenn Kaufman on the National Audubon website: bit.ly/3lQlJLo.

While still a common bird, the white-throated sparrow has shown a gradual but alarmingly steady decline in numbers across its substantial range over the past few decades, slipping by a percent or two per year on average. In Massachusetts, the breeding distribution of the species shrank remarkably between breeding bird atlas projects in the 1970s and in 2007-2011. Formerly a nearly statewide breeder (though as far as I know it has never nested on the Vineyard), white-throated sparrow is now limited to higher elevations in the interior. No wholly convincing explanation of this decline has been advanced.

Vast tracts of seemingly suitable nesting habitat remain in the breeding range of this species across, mostly, southern Canada (young coniferous woodland and woodland edges are preferred, though this sparrow seems quite flexible in its needs for nesting). So a better explanation for the decline in numbers may be mortality on the wintering grounds.

My personal hypothesis, worth precisely nothing, is that the vast expanses of suburban habitat humans have created are both enormously attractive to white-throated sparrows, and laden with perils for the species. These birds love our landscaping and bird feeders but are notably prone to breaking their necks by flying into windows. And their fondness for coalescing around feeding stations and foraging on the ground may make them especially vulnerable to predation by hawks and domestic cats.

So perhaps these birds would be better off without us. But for now, at least, the white-throated sparrow remains a plentiful and most welcome addition to our winter landscape.