Habitat

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.

Behavior

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.

Food

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.