"Is not.” "Is so.” "Is not.” "Is so.” I have the same good-natured debate every summer after a small, pale bird shuffles out from the cattails, its long tail cocked high over its back. The conversation always happens while I’m looking for birds along the edge of a southeastern Arizona pond with a visiting birdwatcher who lives in an eastern or northern state.
"Song Sparrow,” I say. My companion scoffs. Don’t I know that the abundant and familiar bird is chocolate-brown and striped with a big, black spot in the center of its breast? The creature in front of us is light reddish and gray, and its underparts show a few narrow, rufous streaks. It must be some sort of wren, a Fox Sparrow or — this is Arizona, after all — a rare vagrant from Mexico.
Just as my companion is about to lose all faith in me, the bird lets loose with a Song Sparrow’s unmistakable low-pitched "jimp.” What happened?
Over much of the United States, Canada and some portions of Mexico, the Song Sparrow (Melospiza melodia), stands out as one of the most common and confiding of its avian tribe. It is a frequent sight in back yards, marshes and weedy field edges from Alaska to Florida, from the Bay of Fundy to the Sea of Cortez. Over this vast range, the Song Sparrow earns accolades as one of the most geographically variable birds in the world, with two dozen or more subspecies recognized by ornithologists.
Our Arizona encounters involve a member of the notoriously pale subspecies known as Desert Song Sparrow, a common year-round resident of moist habitats in the arid Southwest. These unusually colored songsters, with their equally unusual habit of raising their tails at an angle to their bodies, have confused observers since they were discovered. In the formal description of the bird in 1854, Spencer F. Baird gave the new subspecies the fitting scientific name fallax, meaning "deceptive” or "tricky.”
Variety is the Spice of Life
Learning about geographic variations within a species might seem tricky at times, but as the Song Sparrow shows, it can add a great deal of enjoyment to our observations of even the most common birds. Another abundant sparrow, the Dark-eyed Junco, provides a particularly rewarding opportunity to see variation. A very widespread breeder in the North, the West and the Appalachians, and among the most reliable visitors to wintertime feeders across the United States, Dark-eyed Juncos might be divided into fewer subspecies than Song Sparrows, but they are hardly less extravagantly diverse.
The 15 or so subspecies of the Dark-eyed Junco fall into several recognizable "types.” The widespread western, or Oregon, group includes subspecies with notably dark, slaty heads and breasts that contrast strongly with their bright brown backs and sides. Birds of the slate-
colored group, largely northern and eastern in their territories, appear uniformly gray or brownish-gray with bright white bellies. White-winged juncos — large and pale, with mostly white wings and tails — breed in ponderosa pine forests in South Dakota, Wyoming and Nebraska. Gray-headed juncos, which nest in the Rocky Mountains from Idaho to northern New Mexico, are large with gray flanks and bright rusty backs; their southern counterparts, the red-backed juncos, differ in their dark bills. Finally, the pink-sided juncos are as cute as their name suggests — pale-headed, pastel versions of the Oregon junco with a peachy breast.
They’re all "just” Dark-eyed Juncos, members of what is currently considered the single species Junco hiemalis, but we can find pleasure and excitement when scanning through the winter flocks. Even if our searches do not turn up an out-of-range Oregon junco in the East or a slate-colored in the West, they might reveal variation of another sort.
Birds can show individual differences, and though not all of those differences are obvious to us, some of them are. A tiny percentage of otherwise "typical” slate-colored juncos, for example, exhibit narrow but well-defined white wing bars; many such birds also have conspicuous white eye rings, giving them an oddly appealing "goggled” look.
Even rarer than such leucistic birds — individuals with unusually pale feathers or white patches in the plumage — are complete albinos, which lack pigment in every part of the body including the bill, feet and eyes. These striking mutants tend to draw the attention of predators, but some survive, often with the help of birdfeeders, where they quicken the pulse of human observers.
In a number of familiar species, individual variation is stereotyped, and birds can be assigned to "morphs,” regularly occurring color variations not determined by geography, age or sex. Snow Geese, for example, come in blue and white morphs, while Swainson’s Hawks appear in a wide range of morphs, from black to rufous to startlingly pale.
Sparrows once again provide an especially fascinating example. The abundant White-throated Sparrow occurs in tan-striped and white-striped morphs. Scientists have discovered that white-striped adults excel at defending territories, while tan-striped birds have special talents in nurturing the young. As a result, the most successful White-throated Sparrow pairs — with "success” defined as raising many young during the nesting season — consist of one bird of each morph.
When we learn to recognize variation in our common backyard birds, it opens a window into the ways that nature uses difference, constantly transforming what we might think of as merely "the same” into something fascinatingly new. As a careful observer, you will find that even a Song Sparrow can open that window for you.