Birder’s Notebook: American Tree Sparrow––A “tree” sparrow in name only

The American tree sparrow is usually one of the first spring migrants to slip discretely into the region, perhaps unnoticed by most. Unlike snow buntings and redpolls that arrive in noisy flocks, tree sparrows come quietly and alone or a few at a time, often in late April.

In early spring these long-tailed, rusty-capped, puffy-looking sparrows can be seen pecking for seeds and insect larvae on exposed ground in town and along roadsides, or hopping along river shorelines or ice edges where current washes aquatic invertebrates up for grabs. Finding food in a still wintry landscape is essential––they need to eat 30 percent of their body weight each day or risk hypothermia, rapid weight loss and death.

As is often the case, a tree sparrow was the first migratory songbird to appear at our Banner Creek bird feeder this spring, feeding on spilled seed beneath the feeder rather than on it.

The name American tree sparrow long puzzled me given that this little bird usually forages and nests on the ground and breeds mostly in shrubby habitats of the far North, at or above treeline. The sparrow was given this misleading name by European settlers who were reminded of the Eurasian tree sparrow of their homeland.

In the past, tree sparrows have been outnumbered at our feeder by hordes of hungry redpolls and a wave of larger, more dominant sparrows––golden-crowned, fox and white-crowned sparrows––that usually arrive soon after the tree sparrows lead the way. But this spring, redpolls were strangely absent and we had six days to get better acquainted with tree sparrows before the bigger, bossy sparrows arrived, driving them to the sidelines.

Male tree sparrows sing a clear musical song, but when the birds first arrived, they were silent and intent on feeding. They hopped vigorously back and forth while scratching the snow to revel a winter’s worth of spilled seed from below the feeder, retreating to the willows when alarmed. Occasionally one would launch from a willow branch in a quick burst of flight to snatch a large, newly emerged fly from the air.

Gradually silence turned to whispers and finally, after several days, the males around Banner Creek were belting out their distinctive melody for all to hear, as they claimed their territories. Now theirs is just one of many tunes amidst all the other cheery sparrow songs.

Tree sparrows nest in open or scrubby habitats across Alaska and northern Canada. They are one of the most common and widespread songbirds on the Seward Peninsula.

The male usually selects a breeding territory near water that includes at least a few small shrubs to serve as pedestals from which he can sing to stake his claim and attract a mate. Intruding tree sparrows are vigorously chased away.

The female builds the nest, usually on the ground at the base of a low shrub. The nest is an open cup of grasses and moss, lined with feathers, usually from a ptarmigan.

Incubation is by the female, but both parents feed their three to six nestlings and rear the young. Eight to ten days after hatch, before they can fly, the chicks leave the nest, sometimes coaxed out by the parents with food offerings. Their flight feathers fully develop about two weeks after hatch, but their parents continue to feed them until they are three to fourweeks-old.

The tree sparrow diet shifts with the seasons, but their menu is a combination of seeds, berries and insects.

During the breeding season, insects and spiders are most important and provide the young with the protein needed for growth. During the rest of the year, their diet is almost entirely seeds and other vegetable matter.

Tree sparrows feed mostly by hunting, pecking and scratching on the ground for insects and seeds. They also search through the shrubbery for insects and occasionally hawk flying insects from the air.

By mid-September most tree sparrows have left the Seward Peninsula for their wintering areas across much of the Lower 48 states. There, they can be found in weedy fields, marshes, open forests, gardens and backyards with bird feeders.

Although tree sparrows breed in undisturbed areas of the North and have adapted well to the populated areas where they winter, the population is estimated to have declined by 53 percent between 1970 and 2014. Extensive loss of the weedy, open habitats where the overwintering sparrows forage is thought to be a main factor contributing to the declining numbers of tree sparrows and many other open-country, grassland species.

American tree sparrows are still very numerous, so there is still time to protect critical habitats for this species and others to help prevent further declines.

FORAGING – In spite of their name, American tree sparrows spend much of their time foraging on the ground. This lively tree sparrow hopped and scratched in the snow around our bird feeder to uncover fallen seeds from the snowy landscape. The dark-gray, central breast spot and a bicolored black-and-yellow bill are distinctive features of American tree sparrows. A larger, more dominant, reddish fox sparrow was foraging behind the tree sparrow.

SONG PERCH – Male American tree sparrows try to find breeding territories with at least a few taller shrubs from which to sing. This male had been singing loudly and sweetly to attract to a mate and claim the area as his own. Only the males sing, but males and females communicate with a variety of identical calls. The sexes look alike, and only this bird’s singing gave away his gender.