[5] Much of the confusion seems to have stemmed from a serious lack of knowledge about the anatomy and life history of the species included in the genus.

[11] The sparrow has a long tail, gray-brown with white corners, and has dark marks on the back and sides.

This species is most easily identified by its distinctive song and dramatic skylarking behavior during the breeding season.

Feathers in the upper tail coverts have a gray edge, a brown center, and a black subterminal crescent.

This is sometimes noticeable on a bird flushing or flying away, but it is not always apparent, and by late summer, pale tips may be partly or completely worn away.

[15] Some birds, mainly in the eastern part of their range, tend to be more rufous above, slightly buffier below, and have plainer tails with less obvious shaft streaks and barring on the central rectrices.

[16] Although rarer, even in the eastern part of the range, the rufous morph has been observed as far away as the Farallon Islands off California.

The males sing from February to September[22] with the song of Cassin's sparrow being its most identifiable trait.

[25] Cassin's sparrows also give a variety of chitter calls and chip notes that have been assigned various roles by different authors, including pair bond maintenance, communication with fledglings, alarm calls, territory defense, etc.

[27] Territorial males sit in low bushes or grass, or on the ground to sing, but often give spectacular flight-songs.

Song can be heard from mid-February to early September, depending on location, with considerable night singing at the height of the season reported by some.

[30] The summer diet of Cassin's sparrows consists primarily of insects, especially grasshoppers, caterpillars, and beetles.

Additional insects specifically mentioned in the literature include true bugs, ants, bees, wasps, weevils, spiders, snails, and moths.

However, Wolf (1977) reported that the stomachs of ten adults taken during the breeding season (late June and early July) contained animal and vegetable matter in about equal proportions (52% and 48%, respectively; range = 5–95%).

He also found that five migrant Cassin's sparrow stomachs contained 99% animal material (range = 90–100%).

There is a report of Cassin's sparrows eating flower buds of blackthorn bush (Condalia spathulata) in season.

[34] Oberholser (1974) particularly mentions the consumption of seeds of chickweed (family Alsinaceae), plantain (Plantago spp.

Schnase (1984) reports observing birds drinking water from a small pool immediately following a rain.

Schnase (1984) also noted that the mesquite thickets within Cassin's sparrow territories were distinctly preferred when fledglings were present.