About Passerculus sandwichensis (J.F.Gmelin, 1789)
The Savannah sparrow (Passerculus sandwichensis) has a typically sparrow-like dark-streaked brown back, and whitish underparts with brown or blackish streaking across the breast and flanks. It has whitish stripes on its crown and supercilium, which sometimes show yellow coloring that is more common near the beak. Its cheeks are brown and its throat is white. The flight feathers are blackish-brown with light brown or white borders. Its eyes are dark, its feet and legs are horn-colored, the lower section of its bill is also horn-colored, and the upper section of its bill is dark grey. This is a highly variable species with numerous subspecies, and several of these subspecies have been classified as separate species at different points in time. Different forms of the species vary primarily in how dark their plumage is. This variation generally follows Gloger's rule: Alaskan and interior races are the palest, while southwestern coastal forms are the darkest. There are some exceptions to this rule, most noticeably in some island populations that were likely strongly affected by founder effects. The overall pattern of variation has a fairly clear dividing line; southwest of this line, the birds become notably darker, and this divide matches quite well with the boundary between P. sandwichensis and P. (s.) rostratus. Savannah sparrows also vary in size across their subspecies. Total body length ranges 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 ranges from 15 to 29 g (0.53 to 1.02 oz). For the nominate subspecies, average body weight is 20.1 g (0.71 oz). Core Savannah sparrow populations are very similar to one another, and migrant individuals usually cannot be assigned to a specific breeding population with certainty. Resident or partially migratory subspecies can be clearly distinguished by their size, and particularly by their coloration when comparing between different groups. This passerine bird breeds in Alaska, Canada, the northern, central, and Pacific coastal regions of the United States, Mexico, and Guatemala. Pacific and Mexican breeding populations are resident, while other populations are migratory and winter from the southern United States, across Central America and the Caribbean, to northern South America. It is a very rare vagrant in western Europe.
