The first challenge with this bird is to place it in the correct group of birds. The overall brownish coloration combined with relatively short primary projection and streaked mantle should be enough to get us to sparrows. A handful of people thought this was a raptor, but even if we can't judge the size, the relatively long tail, short wings, and heavily streaked mantle are enough to eliminate any raptor. (e.g. Prairie Falcon would have much longer wings and lack the streaked mantle).
Once we get to sparrows, our challenge becomes greater. The most distinctive thing about this bird may be the rufous lateral crown stripes, the grayish median crown stripe and weak white wing bars. This overall pattern brings to mind immature White-crowned Sparrow. Pacific populations of White-crowned Sparrows have much shorter primary projection than our bird. But even Taiga and Interior West birds would appear slightly shorter winged. More specifically, they would not show the relatively large spacing between the primaries that is shown by this bird. Interior populations also have brighter mantles with a combination of blackish and pale streaking—our bird seems to have blackish streaking on a brownish back, without the pale streaking. Looking at the wing bars more critically, we see that they do not have the strong rufous tones that are typically shown even on relatively worn immature White-crowned Sparrows.
What about Rufous-crowned Sparrow? While the crown pattern may be okay, our bird appears to have a blackish eyeline, or at least dark color to the back of the auriculars. The primary projection is also far too long for the very short-winged Rufous-crowned Sparrow.
Looking more closely at the left side of the cheek, we see a whitish colored spot bordered by blackish—a feature that looks most like what we would expect on a Lark Sparrow. The wing length is also perfect for a Lark Sparrow. While we can't make out the distinctive pale patch at the base of the primaries, some of the greater coverts are covering the bases to the primaries. The pattern of the black-streaked mantle is also perfect for Lark Sparrow. If you look carefully at the right side of the tail, you may also make out the white edge to one of the outer tail feathers. Still unconvinced? In the field, you can always wait for it to turn!

I photographed this Lark Sparrow in mid-June of 2004 in near Navajo Res., Archuleta Co., Colorado.
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The following people (listed by submission date beginning with the earliest) submitted correct answers for the July Bird Photo Quiz—Lark Sparrow:
As stated in the quiz rules, answers must consist simply of the Common or English name exactly as it appears in the ABA Checklist.
The following list shows the number of submissions for each species guessed.
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The photo and answer for this quiz were supplied by Chris Wood.