American tree sparrows are small, grayish-brown birds with a rufous crown and eyeline, a dark spot on the breast, a long notched tail, a dark upper mandible and a yellow lower mandible. They have a grey head, chin, throat, breast and underparts and a rufous patch on the sides of their breast. Males and females are similar in appearance. Juveniles are similar to adults, but have streaking on their sides and breast.
Adult American tree sparrows weigh 18 to 26 g, and are 14 to 16.5 cm in length. Their wingspans range from 21.6 to 24.8 cm.
Baumgartner (1938) followed birds for the first 22 days of development. Order of hatching was not dependent on the order of laying. Earlier hatched birds took the lead in development. During the nine and one-half days in the nest, the four feather tracts of the birds (dorsal, ventral, alar, caudal) go from completely bare to the back covered, lower belly slightly bare, wings 2/3 grown, and tail still a stub, and the birds grow from 1.62 gm to 16.7 gm, while their length goes from 33 mm to 75 mm during the same period. They lose 1.5 gm the first day out of the egg but have gained 3 gm by day 21 (Baumgartner, 1968). On the second day after hatching the young were able to stretch for food. On the fourth day their eyes were half open, after the fifth day, wide open. The first sounds were made on the fifth day but were very soft. Fear was acquired between 7.5 and 8 days as demonstrated by their raucous calls when touched by humans.
During the first 12 days of the fledgling period (which lasts until about a month after leaving the nest in Spizella arborea) the birds showed a steady increase in both tail length (14-47mm) and wing length (46-68mm). At the end of the first 21 days the wings were still slightly shorter and the tails about 2/3 the length of mature birds. A tree sparrow was observed to fly 30 or 40 ft fifteen days after hatching, and a little before one month after hatching, the birds could fly all around their territory (Baumgartner, 1938).
American tree sparrows breed once per year.
American tree sparrows breed between May and August.
American tree sparrows are migratory. Though they are diurnal during the rest of the year, this species migrates at night.
American tree sparrows are territorial during the breeding season. Males sing to claim territories and are responsible for territory defense, though females also occasionally chase intruders. The inner part of a territory is used the most and mainly early in the day, with activity spreading to the outside of the territory later in the day. American tree sparrows do not actively defend winter territories. During the winter they form foraging flocks in which dominance hierarchies develop.
American tree sparrows are omnivorous; they eat a wide variety of seeds, berries and insects. During the winter, American tree sparrows mainly eat grass and weed seeds. During the summer, they primarily eat insects and spiders.
Known predators of American tree sparrows include northern goshawks (Accipiter gentilis), sharp-shinned hawks (Accipiter striatus), screech owls (genus Otus), pygmy owls (genus Glaucidium), Cooper's hawks (Accipiter cooperii), American kestrels (Falco sparverius), weasels (family Mustelidae), foxes (family Canidae) and red squirrels (Tamiasciurus hudsonicus).
There are no known adverse effects of American tree sparrows on humans.
Two geographic races are recognized based breeding location. Spizella arborea arborea breeds from the Atlantic coast all the way to the east of the Yukon. Spizella arborea ochracea breeds around and in the Yukon and Alaska.
"The ground color of the back is decidedly paler than the eastern examples, bringing out the dark streaks in sharper contrast, which is heightened by the absence of their usual chestnut edging; ash of throat and sides of head is much fainter, in many places replaced by brownish fulvous; the underparts, especially the sides and abdomen, are more strongly ochraceous; and the broad ashy crown patch gives the head a very different appearance."
Males of both races generally winter farther north than females.
Ernest Travis (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
Alsop, F. 2001. Birds of North America, eastern region. New York, NY: DK Publishing, Inc.
Baumgartner, A. 1968. Tree Sparrow. U.S. National Museum Bulletin, 237: 1137-1165.
Baumgartner, M. 1938. A study of development of young tree sparrows at Churchill, Manitoba. Bird-Banding, 9(2): 69-79.
Baumgartner, M. 1937a. Enemies and survival ratio of the tree sparrow. Bird Banding, 8(2): 45-52.
Baumgartner, M. 1937b. Food and feeding habits of the tree sparrow. The Wilson Bulletin, 49(2): 65-80.
Baumgartner, M. 1937c. Nesting habits of the tree sparrow at Churchill, Manitoba. Bird Banding, 8(3): 99-108.
CWBO, 1997. "Chipper Woods Bird Observatory: American Tree Sparrow" (On-line). Accessed 03/03/04 at http://www.wbu.com/chipperwoods/photos/treesparrow.htm.
Cornell Lab of Ornithology, 2003. "American Tree Sparrow" (On-line). Cornell Lab of Ornithology, All About Birds. Accessed March 04, 2004 at http://birds.cornell.edu/programs/AllAboutBirds/BirdGuide/American_Tree_Sparrow.html.
Forbush, E., J. May. 1939. A natural history of American birds of eastern and central North America. USA: Houghton Mifflin Company.
Hamilton, T. 2000. Winter Population Trends of Six Species of Sparrows. Bird Observer, 28(3): 154-163.
Kaufmann, K. 1996. Lives of North American Birds. USA: Houghton Mifflin.
Knappen, P. 1934. Insects in the winter food of the tree sparrow. Auk, 51: 93.
Lima, S. 1995. Back to the basics of anti-predatory vigilance: the group-size effect. Animal Behaviour, 49: 11-20.
McNicholl, M. 1987. Communal sheltering under snow by American Tree Sparrows. Ontario Birds, 5(3): 111-113.
Naugler, C. 1993. American Tree Sparrow (Spizella arborea). Pp. 1-12 in A Poole, F Gill, eds. The Birds of North America, Vol. 37. The Academy of Natural Sciences, Philadelphia, and The American Ornithologist's Union, Washington, D.C.