The Carlisle Mosquito Online

Friday, December 3, 2010

 

American Tree Sparrow

Tree sparrows can often be seen drinking from or bathing in small pools of water, sometimes eating snow to take in moisture. (Photo by Alan Ankers)

The American Tree Sparrow is one of those birds dismissively labeled by some as LBJ’s – “little brown jobs.” Sparrows are the charter members of this informal group which also includes the females of such species as House Finch and Indigo Bunting. There are 50 species of sparrow that occur with some regularity in the U.S., and many birders wonder if it is really necessary to have so many. British transplants in particular are keen to point out that they have just two species of sparrow to keep track of, which seems much more reasonable. Our native sparrows are in a different family from those European sparrows, which include the familiar House Sparrow, introduced on this side of the Atlantic by a misguided soul who thought the American avifauna would be somehow deficient without all of the birds mentioned in Shakespeare.

Identifying these small, nondescript birds can indeed be a daunting task. Fortunately, the American Tree Sparrow has a few distinguishing features that make it relatively simple to separate from the others, making it an excellent place to start for those wishing to unravel the mysteries of sparrow identification.

The breast is clear, not streaked like a Song Sparrow, colored pale gray with buffy flanks and a small central black patch often likened to a stickpin, its most distinctive feature. The back is generally a warm reddish-brown, with two white wing bars. The face is gray overall, with a solid rufous crown and eyestripe. A close look at the bill will show the two mandibles to be different colors: yellow below, black on top. One of the tree sparrow’s calls is a delightful soft, sweet, melodic “teedlee-o.” The scientific name Spizella arborea has essentially the same meaning as the common name, except that, just to keep things sufficiently confusing, spizella means finch and not sparrow.

Tree Sparrows are short-distance migrants, breeding in the arctic tundra and wintering across the central and northern United States. Like two of their close relatives, the Junco and White-throated Sparrow, they will be with us all winter. This species has a perfect attendance record on the Carlisle portion (south of rt. 225) of the Christmas Bird Count, with numbers varying from 8 to 127. Unlike most of our avian winter visitors, the tree sparrow’s migration patterns are believed to be related to weather more than food availability. In the summer it feeds primarily on insects, but in winter it switches over to seeds, buds and catkins, mainly gleaned from the ground or low-lying foliage. This is a great redeeming feature of tree sparrows: rather than skulking deep in the undergrowth or flitting around high tree branches, they usually perch in the open at eye level, saving the birder from much effort and a stiff neck. They form loose flocks in winter, typically of about six to 12 individuals.

For many keen birders, late fall is sparrow season. After the warblers and other flashy species have headed south, many different sparrow species come through, and sorting out the subtle differences can be an enjoyable challenge. Perhaps (like candied acorns) it is an acquired taste. Migrating sparrows tend to favor brushy areas and weedy field edges where they can find seeds to eat. My favorite sparrow spots in Carlisle are Foss Farm (especially the few less-fastidiously maintained lots in the Community Gardens); the Acorn trail portion of Great Brook Farm State Park; and the Cranberry Bog, particularly the manure pit on the opposite side of Curve Street, which is probably not a place I would otherwise frequent. I saw my first Tree Sparrow this fall on October 28 at the Cranberry Bog, and since then I have found them in several other places. They supposedly patronize feeders, but the local ones apparently did not get that memo and there is still no Tree Sparrow on my yard list.

References:

The Birder’s Handbook, Ehrlich, Dobkin and Wheye; The Sibley Guide to Birds; The Stokes Field Guide to the Birds of North America (a new photographic guide by former Carlisle residents Donald and Lillian Stokes; its heft makes the term “field guide” questionable).

Field trip:

Meet at 8:30 a.m. on Sunday morning, December 5, at Foss Farm – let’s go and find some Tree Sparrows. ∆


© 2010 The Carlisle Mosquito