- 5.5 in
- 9.4 in
- 0.5–1 oz
- About the size of a House Sparrow.
- Bruant hudsonien (French)
- 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. Their body temperature drops and they lose nearly a fifth of their weight in that short time.
- Like many songbirds, American Tree Sparrows synchronize hatching and fledging so all of the chicks join in the foraging pretty much together. Although the female lays only one egg per day until she's got 4 to 6 eggs (and may even skip a day between eggs), the chicks hatch within hours of each other and may not even hatch in the order their eggs were laid.
- The longevity record among banded American Tree Sparrows is 10 years 9 months.
- 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.
In summer, American Tree Sparrows breed near the northern treeline, where straggling thickets of alder, willow, birch, and spruce give way to open tundra. Though some American Tree Sparrows nest in open tundra, most territories include at least a few small trees that the males can sing from, along with a source of water. During spring and fall migrations, they'll search out weedy fields, marshes, hedgerows, and open forests for foraging between nights of flying. They winter in similar habitats in their southern range, adding gardens and backyards with feeders in settled areas.
American Tree Sparrows eat seeds, berries, and insects, but the relative proportions of those foods change radically from winter to summer months. From fall through spring, they're almost exclusively vegetarian, eating grass, sedge, ragweed, knotweed, goldenrod, and other seeds, as well as occasional berries, catkins, insects, insect eggs, and larvae. In settled areas, they happily eat small seeds from feeders—including millet scattered on the ground. In summer, after their migration north, they begin eating a wider and wider variety of insects until, during June and July they eat almost exclusively insects such as beetles, flies, leafhoppers, wasps, moths, and caterpillars, as well as spiders and snails. These protein-rich foods are particularly important for the growing chicks. Once the chicks are gone, their diet begins reverting to its winter pattern. They may augment their summer food with seeds from alder, spruce, blueberries, and cranberries.
- Clutch Size
- 4–6 eggs
- Egg Description
- Pale blue with reddish speckling.
- Condition at Hatching
- Helpless with sparse tufts of brownish gray down.
Open cup of moss, grasses, shreds of bark and twigs, lined with fine grass and feathers (usually from a ptarmigan). Placed on or near ground, often in tussock of grass at base of shrub.
American Tree Sparrows nest on or near the ground, often in a tussock of grass at the base of a shrub, occasionally as high as about 4 feet on a limb of a willow or spruce. In open tundra with no trees in sight, the nest may sit on a mossy hummock.
In winter, American Tree Sparrows often forage industriously in small flocks. They scratch the ground for dried seeds, and hop up at bent-over weeds or along low branches gathering catkins or berries. Inventive in their foraging, they've been seen beating grass seedheads sticking up out of the snow with their wings to release seeds they can pluck from the ground. These hardy birds often continue foraging undaunted as winter blizzards roll in. Individuals may take solitary perches on low branches or atop stalks like goldenrod. In their summer range, they search out insects from weeds and bushes, occasionally snatching moths or mosquitoes from the air as well. As their spring migration progresses, flocks dissolve and American Tree Sparrows pair up. Females spend much of their time on the nest they build and rarely venture outside the male's territory. Males roost nearby, visiting the nest frequently. Pairings don't outlast breeding season.
Perhaps as many as 40 million American Tree Sparrows breed in summer across 250 million acres of northern Canada and Alaska, beyond the range of usable timber or arable land, where they're generally little affected by humans. Local populations can be at risk from development, as a study that found American Tree Sparrows with high levels of arsenic compounds in a gold-mining region in the Northwest Territories shows. But common predators like hawks and owls don't threaten overall numbers. During the winter, American Tree Sparrows thrive all across southern Canada and the northern United States. They adjust easily to disturbed habitats and human settlements, flocking around backyard feeders.
- Naugler, C. T. 1993. American Tree Sparrow (Spizella arborea). In The Birds of North America, No. 37 (A. Poole, P. Stettenheim, and F. Gill, eds.). The Birds of North America Online, Ithaca, New York.
Medium-distance migrant. American Tree Sparrows breed in far northern North America and migrate to northern and central North America for the winter, reaching latitudes as far south as northern Arizona, Texas, and Alabama. They migrate at night, often in flocks. Females generally winter farther south than males. The return flight to northern Canada and Alaska coincides with spring snowmelt in the far North.