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A rather dull gray bird with some rufous and dark streaking above and a relatively thick bill (compared to say, a warbler) should quickly call to mind that perennial favorite of birdwatchers—the sparrows. Cactus Wren probably deserves some quick consideration since the bird is in a cactus, but that species has a much shorter bill, conspicuous dark spotting on the underparts and a white supercilium.
Many sparrows can be eliminated rather quickly—longspurs and juncos are very different in terms of overall coloration and pattern. None of the towhees have this type of patterning on the upperparts. While Olive Sparrow shares this individual's largely unmarked underparts, that species would never show the crisp markings on the upperparts and wings.
One way of grouping sparrows is into a group with streaks on the underparts, and a group without. I'm not particularly fond of this technique, since it is complicated by the streaked juvenile plumage of almost all Emberizidae (Emberizine sparrows and their allies). Luckily in our case, our bird only has a bit of streaking on the sides of the breast, so we can eliminate those sparrows with conspicuous breast streaking at all ages-species such as Song Sparrow, Lincoln's Sparrow, Savannah Sparrow, Vesper Sparrow, and most of the Ammodramus sparrows. Grasshopper Sparrow is the only Ammodramus that fits in terms of breast streaking, and I must admit that species can looks quite similar to our bird. Yet, Grasshopper Sparrows are almost always a much richer buff on the underparts and face. Grasshopper Sparrows typically also have a darker (less rufous) spot at the back of the auriculars, and the lores in particular also tend to be ocharaceous to pale buff in color.
Having already eliminated two Melospiza sparrows (Song and Lincoln's Sparrows) we may as well dispatch of the third, Swamp Sparrow. Our first hint should be that our bird is in a cactus—quite different habitat than we would expect to see any Melospiza. Of course, all three species are migratory and could end up in a cactus (indeed, I have seen all three species in cholla in Colorado). Still it's unlikely. Luckily, Swamp Sparrows also don't look terribly similar to our bird. They are gray below and rufous above, but looking more critically we see that the wing coverts on our bird are strongly edged in pale gray (perhaps even whitish) unlike the more uniformly rufous wings of Swamp Sparrow. Swamp Sparrows also have a very uniformly gray nape (our bird has lots of fine markings here).
The most frequently seen group of sparrows with unstreaked breasts as adults in most of North America is the Spizella sparrows (American Tree, Field, Brewer's, Clay-colored, Chipping, and Black-chinned). Each of these species has a bill that should appear smaller and more pointed than our bird and the relatively slender and long-tailed Spizellas should not appear as chunky and big headed as our bird. The nape of our bird is also much too well marked—even the Brewer's Sparrow, which has the most nape streaking of any Spizella, would not show this much patterning to the nape.
We are left with three very similar Aimophila sparrows that look much like our bird: Bachman's, Botteri's, and Cassin's. Bachman's Sparrow is a bird of open pine woodlands—a habitat that looks quite different from where our bird seems to be. Aside from habitat, which should not be underrated in importance, Bachman's Sparrows should appear longer-billed, with a more well-defined supercilium. Many Bachman's Sparrows would also appear more buff colored on the breast.
Botteri's Sparrow is notoriously similar to Cassin's Sparrow, but in the case of a fresh-plumaged bird like we have here, shouldn't present an overwhelming challenge. Botteri's Sparrows are unmarked on the throat and breast, while out bird has fine streaking on the sides of the breast. As we have already noted, our bird has fairly distinct white edging to the wing coverts, a great field mark for Cassin's Sparrows when present. Botteri's Sparrows show much more uniformly gray outer greater coverts that blend into grayish primaries, which combined form a plain unmarked panel on the wings. The bill on this bird is also shorter than we would expect on a Botteri's Sparrow.
I should note that Cassin's Sparrows typically show a more distinct lateral throat stripe than our bird. Unfortunately, posture and individual variation can cloud the usefulness of this in the field. Other features are quite characteristic of a spring or early summer Cassin's Sparrow. This Cassin's Sparrow was photographed in early June in Baca County, Colorado by the author.
The following people (listed by submission date beginning with the earliest) submitted correct answers for the July Bird Photo Quiz—Cassin's Sparrow:
The following list shows the number of submissions for each species guessed.
The photo and answer for this quiz were supplied by Chris Wood.