About Spizella wortheni Ridgway, 1884
Spizella wortheni, also known as Worthen's sparrow, measures 12.5 to 14 cm in length. This species can be identified by its distinct head pattern: a grey head with a rufous crown, a brown postocular stripe, and a pink bill. It has grey-brown upperparts marked with dark brown streaks, a grey underbelly, and dark brown wings and tail. Its wings are edged paler, with a broad whitish to pale buff wing-bar, buffy-rufous edging on tertials and secondaries, and greyish lesser coverts. Juveniles have brownish coloration on the head and chest, with dusky streaking on the head and dark brown streaking on the chest and flanks. The song of this species is a dry, chipping trill that lasts 2–3 seconds, and is described as intermediate between the songs of the field sparrow and the chipping sparrow. Worthen's sparrow is similar in appearance to the field sparrow (Spizella pusilla), but the two differ in plumage, habitat, and song. This species nests from May to July, and usually lays three or four eggs per clutch. After the breeding season, single-species flocks form, and these flocks are strongly attracted to permanent water sources. The species is not migratory. A small number of individuals have been sighted in northwestern Mexico, and only one individual has ever been recorded in the United States. This single U.S. individual was shot by Rieber on June 16, 1884, near Silver City, New Mexico. It was the first individual of the species to be described, and serves as the type specimen. Worthen's sparrow is endemic to northeastern Mexico, and currently occupies a total range of 25 km². Populations were formerly found across Zacatecas, Coahuila, Nuevo León, and Tamaulipas, but the species is now only known to occur from southeastern Coahuila to western Nuevo León. This sparrow prefers open, arid shrub-grassland located at elevations between 1,200–2,450 m (3,940–8,040 ft). It favors open areas with low grasses for foraging, and typically uses low, dense shrubs for nesting and cover. In 2004, the total population of Spizella wortheni was estimated to be between 100 and 120 individuals.
