The American Tree Sparrow has an odd name, since they are rarely seen actually sitting in trees. Most times you see them on the ground. From the Cornell Lab of Ornithology - "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.
Although many aspects of the behavior and natural history of American Tree Sparrows are well studied, gaps still exist in our knowledge of this species; little is known of population structure, population regulation and dynamics, and dispersal, for example. In addition, most studies of the breeding biology of this species have been conducted in northern Manitoba. As American Tree Sparrows breed over a wide geographic area, it is likely that aspects of their biology may differ across their range."