Bird of the Week

Photo courtesy Byron Greco

This week’s Bird of the week, compliments of the Weminuche Audubon Society and Audubon Rockies, is the American tree sparrow.
A compact, round-bodied sparrow with a long tail, this bird can be distinguished from several other sparrow species by a few key characteristics. First, lacking streaking on the breast and underparts like a song sparrow, they have more solid gray/white/buffy underparts, with an isolated dark spot central on their breast. Second, they don a rufous cap and gray face much like the chipping sparrow, but their eyeline is red, unlike the black eyeline on a chipper. Third is the American tree sparrow’s characteristic bi-colored bill with a dark upper mandible and yellow lower one.
These birds feed heavily on seeds in winter. Whether in marshy areas, forested edges or pastures, they will locate bent-over grasses and work diligently to free the seeds. They are more of a ground forager than their name would suggest, oftentimes seen below our bird feeders alongside dark-eyed juncos feeding in the understory. In late spring, their diet begins to shift to insects as they migrate to breeding grounds in Alaska and Canada. Here, as they rear chicks in stunted forests and grass clumps on the tundra, they shift to an exclusively protein-heavy diet of beetles, leafhoppers, moths and caterpillars to boost growth in their young.
As we experience this species primarily on its wintering grounds, we typically only hear their more elaborate songs associated with attracting mates just as they depart, but do hear them communicating regularly through high-pitched ethereal calls, as they move around oftentimes in flocks.
As indicated by years of Christmas Bird Count data, Audubon notes this species to be in a marked state of decline in the southern Rockies/Colorado Plateau region. Efforts to protect habitat on its wintering grounds is critical to bolstering population numbers.
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