A key feature for ID'ing this sparrow is not only the yellowish marking in its facial area (at times not visible) but also the notch in its tail. The Savannah Sparrow (Passerculus sandwichensis) is a small American sparrow. The common name comes from Savannah, Georgia, where one of the first specimens of this bird was collected. This species has a typically sparrow-like dark-streaked brown back, and whitish underparts with brown or blackish breast and flank streaking. It has whitish crown and supercilium stripes, sometimes with some yellow (more often near the beak). The cheeks are brown and the throat white. The flight feathers are blackish-brown with light brown or white border. The eyes are dark. The feet and legs are horn-colored, as is the lower part of the bill, with the upper part being dark grey. The Savannah Sparrow is a very variable species, with numerous subspecies, several of which have been split as separate species at various times. The different forms vary principally in the darkness of the plumage. The variation generally follows Gloger's Rule, with Alaskan and interior races the palest, and southwestern coastal forms the darkest. There are some exceptions, though, most conspicuously in some island populations that presumably were strongly affected by founder effects. The general pattern of variation has a fairly clear divide, southwest of which the birds become notably darker; this agrees quite well with the limit between P. sandwichensis and P. (s.) rostratus. Savannah Sparrows show some variation in size across subspecies. The total length can range from 11 to 17 cm (4.3 to 6.7 in), wingspan ranges from 18 to 25 cm (7.1 to 9.8 in) and body mass from 15 to 29 g (0.53 to 1.02 oz). In the nominate subspecies, the body weight averages 20.1 g (0.71 oz). The Savannah Sparrows proper (see below) are very similar, and migrant birds can not usually be related to a breeding population with certainty. The resident or partially migratory subspecies are well distinguishable by size and, particularly between groups, coloration.