Cassin's sparrow (Peucaea cassinii) is a medium-sized sparrow. This passerine bird's range is from western Nebraska to north-central Mexico. The sparrow has a long tail, gray-brown with white corners, and has dark marks on the back and sides. The species resembles Botteri's sparrow because of its size and marks, but Boterri's sparrow is a weaker shade of gray. The best way to tell the differences between the two is the song of Cassin's sparrow. Both the males and females are the same shade of gray and are 5 to 6 inches, although males are bigger. The Cassin's sparrow is a fairly large, plain, grayish sparrow that lacks conspicuous markings. In flight, the long, roundish tail is obvious and the white tips of the tail feathers are sometimes apparent. This species is most easily identified by its distinctive song and dramatic skylarking behavior during the breeding season.