Spizella arborea
American tree sparrow

American tree sparrows (Spizella arborea) breed throughout almost all of Alaska, the Yukon and Northwest territories, the very north of Manitoba and Ontario, all of Labrador, and in northern Quebec. Their winter range includes a very small part of southern Canada and all of the United States except for the western most 250 miles, the southern most 450 miles and all of Florida. (Alsop, 2001)

The breeding habitat of American tree sparrows is typically near the tree line in open scrubby areas with willows, birches, alder thickets or stunted spruce. They may also breed in open tundra with scattered shrubs, often near lakes or bogs. They winter in open forests, gardens, fields, and marshes. (Naugler, 1993)

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.

There are two recognized subspecies of Spizella americana. The western subspecies, Spizella americana ochraceae is paler and slightly larger than the eastern subspecies, Spizella americana arborea. (Alsop, 2001)

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 are monogamous. Breeding pairs form after arrival on the breeding grounds, around mid-June. Singing is used by both sexes to show their interest in one another. The female becomes excited when a male comes to sing nearby and she utters a "wehy" sound. This serves to attract the male to her. The male may also spread his wings and flutter, dart to the ground in front of the female, then fly back to his perch, and repeat this process several times. Sometimes breeding occurs without any display during feeding or at the nest. Breeding has been observed during nest building and on the day before an egg is laid. The duration of pair bonds is unknown. (Baumgartner, 1937c)

American tree sparrows breed between May and September and raise only one brood per season. The females builds the nest alone. Nests are built on the ground, and are constructed of moss, grasses, bark and twigs and lined with fine grass and feathers. Nest construction takes about 7 days. The female then lays 4 to 6 (average 5) eggs at a rate of one per day. She incubates the eggs for 10 to 14 days and broods the altricial chicks after hatching. Both parents feed the young until they fledge from the nest and for 2 to 3 weeks afterward. The young fledge from the nest 8 to 10 (average 9) days after hatching. In late summer, families join larger flocks. The age at which American tree sparrows begin breeding is unknown. (Baumgartner, 1937c; Cornell Lab of Ornithology, 2003; CWBO, 1997; Naugler, 1993)

Females incubate the eggs and brood the altricial chicks when they first hatch. After a few days, the females spend more time feeding the young and less time brooding. Males also help feed the young. One male sparrow was observed leading a chick out of the nest by offering it food. Feeding by the parents ends when the chicks are about 22 days old. (Baumgartner, 1937b; Baumgartner, 1938)

The oldest known American tree sparrow lived at least 10 years and 9 months. The average life expectancy for American tree sparrows is 2.3 to 3.4 years. (Baumgartner, 1937a; Baumgartner, 1968; CWBO, 1997; Naugler, 1993)

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 move by hopping on the ground and on branches, and by flying. They do not swim or dive, but do bath frequently. They roost solitarily in conifers, thick bushes, haystacks, cornfields, and marshes. In winter, they may shelter communally under the snow. (McNicholl, 1987; Naugler, 1993)

We do not have information on home range for this species at this time.

American tree sparrows communicate using sounds and physical displays (see Mating Systems section for examples). Only male American tree sparrows sing, though both sexes use calls. The songs of American tree sparrows are composed of high, thin whistles and last 1 to 2 seconds. They are used primarily in territorial defense and to attract mates. Each male sings only one song. Both males and females use calls, which appear to be associated with particular behaviors such as feeding or alarm. Chicks use calls to express hunger, discomfort, and fear beginning at 5, 6, and 8 days old, respectively. (Baumgartner, 1938; Cornell Lab of Ornithology, 2003)

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.

American tree sparrows forage among vegetation on the ground and along the branches and twigs of shrubs and trees. In Massachusetts, they are frequently seen in flocks that seem to roam from bird feeder to bird feeder. American tree sparrows drink about 30% of their body weight in water each day. During the winter, they obtain water by eating snow. (Baumgartner, 1937b; Cornell Lab of Ornithology, 2003; Hamilton, 2000; Knappen, 1934)

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).

When approached by humans, American tree sparrows give a rapid series of "tset" calls. It is unknown how American tree sparrows respond to other potential predators. (Naugler, 1993)

American tree sparrows play an important role in their local communities. They eat many seeds, insects and spiders and are an important food source for their predators. (CWBO, 1997)

American tree sparrows may benefit farmers by removing weed seeds from their fields. The U.S. Department of Agriculture estimated in 1937 that sparrows, American tree sparrows included, saved farmers $90,000,000 per year by removing weed seeds. (Baumgartner, 1937b; Baumgartner, 1968)

There are no known adverse effects of American tree sparrows on humans.

American tree sparrows are abundant and widespread. There are approximately 26,000,000 American tree sparrows throughout their range. American tree sparrows are protected by the US Migratory Bird Treaty Act, but have no special status under the U.S. Endangered Species ACT or CITES. (Kaufmann, 1996; Naugler, 1993)

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.

Spizella arborea ochracea was first recognized as a subspecies in 1881 by William Brewster. He describes them as:

"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.

Spizella arborea arborea is sometimes called "eastern tree sparrow", "winter chippy" and "Canada sparrow". (Baumgartner, 1968; Forbush and May, 1939)