Original description: Zonotricha Cassinii Woodhouse 1852
Taxonomic history in AOU/AOS Check-list
AOU 1 (1886): Cassin’s Sparrow, Peucaea cassini
AOU 2 (1895): Cassin’s Sparrow, Peucaea cassini
AOU 3 (1910): Cassin’s Sparrow, Peucaea cassini
AOU 4 (1931):Cassin’s Sparrow, Aimophila cassini
AOU 5 (1957): Cassin’s Sparrow, Aimophila cassinii
AOU 6 (1983): Cassin’s Sparrow, Aimophila cassinii
AOU 7 (1998): Cassin’s Sparrow, Aimophila cassinii
IUCN Conservation Status: Of least concern
Behavior: The Cassin Sparrow is among the shyest and most easily overlooked of the sparrows. Virtually all foraging takes place on the ground beneath dense grass, where the birds hop and walk. Startled, they may run away beneath the vegetation before flushing; like Bachman Sparrows, they are known to use rodent burrows as shelter from potential predators. The flight is surprisingly strong and direct, but at least on the breeding grounds always low over the grasses; migrants presumably fly at greater heights.
Males sing from scattered bushes in their breeding territory, often from the top but sometimes just below and inside the crown. The extravagant flight song takes the male twenty feet or more into the air above his perch, where he stalls and slowly floats down to a bush top or sometimes the ground, tail spread and feet dangling. The introduction to the song is uttered at take-off or on the ascent, the tremolo and concluding notes during the slow descent.
Voice: Many birders see their first Cassin Sparrow during the birds’ breeding season, when the male’s sad, silvery song renders visual identification secondary. Adolphus Heermann was the first to note the distinctive song flight:
“Rising with a tremulous motion of its wings some twenty feet or more, it descends again in the same manner to within a few yards of the spot whence it started, accompanying its entire flight with a lengthened and pleasing song.”
Oddly, Heermann had nothing more to say about the song, though that was what had alerted him to the presence of the bird in the first place. Others on encountering the species would also remark on “its sweetly modulated song,” but an actual description of the notes and phrases was not published until 1875, when Henry Henshaw finally provided an account of the Cassin Sparrow’s “very plaintive, but quite pretty and attractive” melody:
“It begins with a low tremulous trill, followed by slow and plaintive syllables, the last of which is softer and more prolonged, and in a lower key. Though little varied, and on this account somewhat monotonous, it yet possesses and indescribable sweetness and pathos, especially when heard, as is oftne the case, during the still hours of the night.”
Few observers would not agree that this is one of the most evocatively beautiful and regularly melodious of all passerellid songs. It typically starts with one or two very quiet but round, rich notes followed by a broad, loose, silvery tremolo in an impassioned crescendo; the bird inserts the most vanishingly momentary of pauses after the tremolo, then sings two finer, faintly trilled notes, the last lower by a full step than the one before it. Heard from a great distance across the desert grassland, the descending conclusion can strike the ear as disconcertingly similar to the spring “phoebe” song of a Black-capped Chickadee.
Males may also sing a secondary song, similar to the familiar primary song but introduced by a “series of chips, trills, and buzzy notes”; this song is given at early stages of the nesting cycle, presumably at least in part to reinforce the pair bond. The “whisper song,” performed in late summer, is “very soft [and] consists of a few preliminary notes, then [an] assortment of trills”; very variable, this song may go on for several minutes.
When not singing, Cassin Sparrows are relatively quiet. They may give a stuttering tsitsi when flushed, or a soft, dull tip in alarm at the approach of a human observer.
Detailed description and measurements drawn from standard reference works
Adult: Tail feathers dark brownish gray, the central pair grayer and faintly paler with narrow blackish shaft streaks extending onto webs to create short, jagged, irregular bars. Upper tail coverts and rump feathers sandy brown with narrow blackish shaft streaks, round or shallowly crescent-shaped black spots before the tip, and very narrow pale gray edges and tips. Back feathers and scapulars light brown with slightly darker centers, blackish spots or crescents near tip, and fairly broad light gray edges and tips. Primaries and secondaries dull gray-brown with very faint browner shaft streaks and buffy to buffy whitish outer edges. Tertials dark gray, duskier on inner webs, with neat white edges and tips. Greater and median coverts dull grayish with darker blotches just before tip, in fresh plumage with wide grayish edges and tips; wing bar formed by greater covert tips sometimes conspicuous, that formed by median covert tips rarely so. Marginal coverts of under wing bright pale yellow. Nape gray with narrow brown or reddish brown streaks.
Under tail coverts and vent pale buffy. Belly, breast, and throat pale soft brownish gray. Flanks slightly buffier, with variably heavy dark brown streaks at rear. Pale soft brownish gray throat sometimes with narrow dark lateral throat stripe. Jaw stripe dull buffy.
Crown gray with fine dark brown or sooty streaks. Ear coverts buffy grayish, divided from jaw stripe by inconspicuous darker brown whisker and bordered above by rusty line extending back from eye and curling faintly behind ear coverts. Supercilium and lore grayish to buffy. Fine white ring most conspicuous above and below eye, grayer in front of eye, usually broken by eye line behind eye.
Tarsus and toes pinkish gray. Rather fine, very slightly down-curved bill dull pinkish below and on edges of upper mandible, ridge of upper mandible dark gray.
Juvenile: Tail feathers dark brownish gray, the central pair grayer and faintly paler with narrow blackish shaft streaks extending onto webs to create short, jagged, irregular bars. Upper tail coverts and rump feathers brown with narrow blackish shaft streaks and bars and buffy edges and tips. Back feathers and scapulars dull brown with dark brown shaft streaks and buffy tips. Primaries and secondaries dull brown with very faint browner shaft streaks and thin white outer edges. Tertials dark gray, duskier on inner webs, with white edges and tips. Greater and median coverts brownish, greater coverts edged and tipped white and median coverts edged and tipped dull buffy, the tips producing two weak wing bars. Marginal coverts of under wing pale yellow. Nape feathers brownish gray with narrow pale buffy edges and dark brown or shaft streaks.
Under tail coverts and vent buffy. Belly whitish buff, breast and throat pale buffy gray. Flanks and breast heavily streaked with dark brown streaks. Throat buffy with brown streaks and spots. sometimes with narrow dark lateral throat stripe. Jaw stripe dull buffy.
Crown buffy with dark brown streaks. Ear coverts buffy grayish with brown streaks. Supercilium and lore buffy gray. Fine white ring broken by brown line behind eye.
Tarsus and toes dull pink or gray. Rather fine, very slightly down-curved bill dull pinkish below and on edges of upper mandible, ridge of upper mandible darker gray.
Length 131-147 mm (5.1-5.8 inches)
Wing 59-68 mm (2.3-2.7 inches)
Tail 66-71 mm (2.6-2.8 inches)
Mass 17-19 g