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Bird of the Month: American Tree Sparrow

By Andy McCormick 
Spizelloides arborea
Length 6.25” Wingspan 9.5” Weight 0.7 oz (20 g) 
 AOU code: ATSP  
 
The American Tree Sparrow is always a treat to see. It is a winter visitor to Washington and is most often seen east of the Cascade Range. However, some individuals occasionally stray westward and provide birders in Western Washington with a noteworthy observation. 
This sparrow is readily identifiable with its rufous cap, bicolored bill (yellow lower mandible), and light gray throat and chest with a central dark spot. It has a rufous line through the eye, rufous patches on its sides, and two white wing bars (Naugler, et al).  
 
Its high-pitched song and warbles bring a pleasant voice to the winter landscape. Its call is a soft, jingling teedleoo, and its flight note is a sharp tsiiw (Sibley). You can see and hear an American Tree Sparrow singing at the Macaulay Library. American Tree Sparrow
 
Tundra Is Home
 American Tree Sparrows nest beyond the reach of usable timber and arable land and their nesting habitat is generally not disturbed by human activity (Naugler, et al). They also winter farther north than most other sparrows. Arriving in Washington from mid-October to early November, tree sparrows will be seen in brushy and grassy areas, marshes, and suburban areas foraging for seeds. They will also frequent feeding stations with Dark-eyed Juncos.
 
In late May, tree sparrows arrive on their tundra breeding grounds in northern Canada and Alaska and begin nest building in scrubby areas near the tree line. The open cup nest is usually constructed on the ground or in a shrub within a few feet of the ground. Usually five bluish or light green eggs with dark spots are deposited. Incubation by only the female takes 11-13 days, and first flight follows in another two weeks (Kaufman).
 
Insects and Seeds
Insects make up the bulk of the fledgling’s diet and young birds are fed by both parents for about two weeks after they leave the nest. Adults and larvae of beetles, flies, mosquitoes, butterflies, and moths are included in the diet. Some seeds will be consumed in summer, but a much wider variety of plant seeds are eaten in winter. 
 
Even though American Tree Sparrows migrate south in winter, they have a short migration and still have to contend with winter conditions. Tree sparrows can be seen feeding on bent over stalks of grass, and it has been reported that over snow, these sparrows will beat weeds with their wings and then fly to the snow surface to retrieve the seeds (Naugler, et al). 
 
Research Is Needed 
Although their overall population is considered strong, American Tree Sparrows had a population decline of 53% between 1970 and 2014 (Naugler, et al). Warming in the Arctic region is continuing and it is not known what impact this has had on their nesting process. Their wintering habitat of weedy, early-successional plants has been reduced as a result of agricultural and developmental expansion in southern Canada and northern United States. Further research is recommended to determine the cause of their decline and a focus for a conservation plan. 
 
A Note on the American Tree Sparrow Taxonomy: 
 
American Tree Sparrow was recently assigned its own genus, Spizelloides, combined from its former sparrow genus Spizella, and the Greek –oides, meaning resembling. “The name alludes to the evolutionary convergence in plumage, morphology, and behavior that led to Spelloides arborea being considered a Spizella sparrow for many years” (Slager and Klicka, 2014 doi: 10.11646/zootaxa.3821.3.9).
 
 Mitochondrial DNA testing showed that the American Tree Sparrow is closer genetically to the Passerella (Fox Sparrow), Zonotrichia (White-crowned, Golden-crowned, etc. Sparrows), and Junco genera, than it was to the other Spizella sparrows. The species epithet arborea, was retained. It is from the Latin, of or belonging to trees (Holloway). The American Tree and all other new world sparrows have been split from the family Emberizidae (old world sparrows) and assigned to their own new family Passerellidae in 2017 by the American Ornithological Society.
 
Photo by, Gerald Beyersbergen
References available upon request from amccormick@eastsideaudubon.org
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