The American Tree Sparrow is a familiar migrant and winter visitor in many settled areas of North America, where winter flocks frequent backyard feeders and are important consumers of weed seeds. “American Tree Sparrow” is somewhat of a misnomer for this species, as most individuals breed in remote northern areas, often north of the treeline. The name was given by early European settlers for the superficial resemblance of this species to the Eurasian Tree Sparrow (Passer montanus).
In summer, males sing persistently to proclaim possession of territory. Individual males sing only a single song type each, although song types are widely shared among males. Females build a nest on the ground and incubate the eggs alone. Both parents help to raise the single brood of 4 to 6 young.
This species breeds far north on our continent and has received limited attention to its natural history. Most of the detail of this sparrow's breeding biology is based on general observations of 26 nests and detailed observations at 9 made by A. Marguerite Baumgartner near Churchill, Manitoba (e.g., Baumgartner 1937b, 1938b, 1968). Its winter distribution brings the species to the more populated portions of the continent and here American Tree Sparrows have served as a model organism for investigating the mechanisms of physiological control and timing of gonadal development and regression, and of molt and migration (e.g., Wilson 1985, Wilson and Reiner 1996).