Wild Side: Savannah sparrows

Their variation across the species makes them hard to distinguish in the field.

Savannah sparrows tend to stay in open, grassy areas. —Matt Pelikan

Across its vast geographical range, Savannah sparrows show a remarkable range of variation in features such as bill size, coloration, and preferred habitat. About 28 subspecies of Savannah sparrow have been described; a few, particularly ones with limited ranges on the West Coast, are fairly distinctive, but many of the others can’t be reliably sorted out in the field.

As many as three of these may be regular on Martha’s Vineyard. One of these, the “Ipswich” sparrow, is distinctive enough that it was formerly considered a full species of its own. Large and pale, this bird has a very limited breeding range (essentially just Sable Island, Nova Scotia). In winter, it’s largely restricted to the immediate coast, where it’s found on beaches and dunes, and seems able to forage successfully in incredibly barren and austere locations.

Based on range, the Savannah sparrows that nest on Martha’s Vineyard probably belong to the subspecies Passerculus sandwichensis savanna. P.s. labradorius, a more northern race, must surely pass through with some regularity on migration, and other subspecies no doubt occur here from time to time as vagrants. But the problem with subspecies is that they are, by definition, imperfectly defined. And in the case of the Savannah sparrow, most subspecies show a lot of internal variation. I’ve spent a good deal of time over the years trying to get a feel for our Savannah sparrow subspecies, and I’m about ready to chuck the whole effort in frustration.

I do, though, feel pretty sure that the Savannah sparrows we have in winter are a different set — mostly if not entirely so — from the ones that breed here. Local breeders tend to move off their territories, or at least become a lot less concerned with defending them, in August and September. They probably begin to move southward around then, too, but the departure of our breeding birds is masked by the arrival of migrants from farther north, some of which will remain through the winter most years.

Whether breeding or wintering, Savannah sparrows show pretty much the same habitat preference, and hence tend to turn up in the same places. This makes it even harder to detect the seasonal movements of the species. Savannah sparrows like open, grassy areas, so they both breed and winter in places like Katama Farm, Herring Creek Farm, and the grassland at Long Point Wildlife Refuge. My Christmas Bird Count territory (Vineyard Haven) usually coughs up a small number of Savannah sparrows, but finding them requires a slog along field edges at Thimble Farm. You may find this species in shrubby areas or along weedy woodland edges. But a Savannah sparrow in a densely wooded area is unusual, and this is not a species that tends to turn up at feeding stations very often.

The name of the species comes from the city Savannah, Ga., where it was first described by the great early American ornithologist Alexander Wilson. Savanna (or savannah) describes the habitat type, characterized by a mix of grass and mature trees, that might attract this sparrow in migration, but they really don’t seem to nest much near tall trees. Perhaps such trees, potential perches for hawks, register as threats to a Savannah sparrow.

In high-quality breeding habitat, Savannah sparrow can be a very common and conspicuous bird. Scores nest every year on the native grassland at Katama Airpark, with singing males spaced 75 yards or so apart across the entire site. Up-Island grasslands and pasture at Katama Farm and Herring Creek Farm may have similar densities, and I don’t really know whether Savannah sparrows actually prefer pasture or native grassland; perhaps they don’t care. The nests I’ve found have varied somewhat in their setting: Some have been inside clumps of lowbush blueberry or huckleberry, some have been snuggled in right at the base of a small scrub oak, and a few have been set in open areas under bent-over grass.

Brownish and heavily streaked, these birds are well camouflaged in any type of grassy setting. Territorial males sing quite persistently, especially early in the day, often perching in a shrub or tall weed. The song is distinctive and, while not very loud, can carry an amazing distance if conditions are quiet: a series of three or four faint “tics” followed by two breathy buzzes, the second one lower in pitch than the first one. This species also gives a “tic” call note that is distinctive, at least in the breeding season, when dark-eyed juncos aren’t around to give their similar call.

Assuming anything better than truly brutal conditions this season, some Savannah sparrows (including the beach-loving “Ipswich” type) will likely persist on the Vineyard through the winter. We may have a brief, Savannah-free gap between the departure of those birds and the arrival of our breeders, but for all practical purposes, this tough and wily sparrow is a year-round feature in Vineyard fields and grasslands.