American Tree Sparrows are small, round-headed birds that often fluff out their feathers, making their plump bodies look even chubbier. Among sparrows, they have fairly small bills and long, thin tails. They measure approximately 14 centimeters, with a wingspan of approximately 24 centimeters. A rusty cap and rusty (not black) eyeline on a gray head, a streaked brown back, and a smooth gray to buff breast in both male and female American Tree Sparrows give an overall impression of reddish-brown and gray. A dark smudge in the center of the unstreaked breast is common. Small flocks of American Tree Sparrows hop about on the ground, scrabbling for grass and weed seeds, calling back and forth with a soft, musical twitter. Individuals may perch in the open atop goldenrod stalks or shrubs, or on low tree branches. Look for small flocks of American Tree Sparrows in winter in weedy fields with hedgerows or shrubs, along forest edges, or near marshes. They readily visit backyards, especially if there's a seed feeder. American Tree Sparrows breed in the far north and are rarely seen south of northern Canada in summer. The conservation status of this species is Common Bird in Steep Decline.
Misleadingly named by European settlers reminded of Eurasian Tree Sparrows back home, American Tree Sparrows are ground birds. They forage on the ground, nest on the ground, and breed primarily in scrubby areas at or above the treeline.
American Tree Sparrows need to take in about 30 percent of their body weight in food and a similar percentage in water each day. A full day's fasting is usually a death sentence.
Like most birds, American Tree Sparrows are sensitive to changes in day length, and this doesn't seem to depend on vision. Blind tree sparrows in captivity show normal responses to increasing day length in late winter, including sex organ growth.
Source: American Tree Sparrow Overview and Identification Information, All About Birds, The Cornell Lab of Ornithology.