Distinguishing Characteristics

Large sparrow (emberizid), 15.0–18.5 cm long (Rising 1996), 25–49 g mass, sexually monomorphic. In general, breast and flanks have rufous to sooty-brown streaks, some of which form a central spot on the breast. Wings, upper tail-coverts, and rectrices rufous to dark sooty brown. Mantle coloration gray with rufous streaks, or unstreaked gray to sooty brown. Bill bicolored, with upper mandible blackish brown and basal edges dull orange or yellow. Lower mandible orangish or yellowish with grayish-brown tip. Bill size variable but conical and moderate to heavy in size. Largest-billed Fox Sparrows have deeper bills than all other North American sparrows. Feet and legs pinkish brown to reddish brown; iris dark brown to reddish brown. Through careful consideration of geographic variation in plumage (see Systematics: geographic variation, below), most individuals can be identified to 1 of the 4 major groups of subspecies: (1) Red Fox Sparrow (iliaca group), reddish-plumaged birds, with streaked backs and comparatively shorter tails; (2) Sooty Fox Sparrow (unalaschcensis group), dark-brown or sooty-plumaged birds with comparatively shorter tails and medium-sized bills; (3) Slate-colored Fox Sparrow (schistacea group), longer-tailed birds with gray backs, reddish wings and tails and medium-sized bills; and (4) Large-billed Fox Sparrow (megarhyncha group), longer-tailed birds with gray backs, reddish wings and tails, and large bills.

Distinguished from Song Sparrow (Melospiza melodia) by (generally) larger size (wing 73–92 mm, tail 62–91 mm), shorter deeper bicolored bill, lack of streaking on upperparts (western subspecies), indistinct or no dark streak on malar region, and ventral streaking composed of broader, more triangular markings (Rising 1996, Pyle 1997).