One of the last bird species in the United States to be discovered and described, the Rufous-winged Sparrow is an uncommon resident of local distribution in the Sonoran Desert region from south-central Arizona to northern Sinaloa, Mexico. The first specimens of the species were taken by C. E. Bendire on 10 June 1872, near Fort Lowell (i.e., Tucson), Arizona ( Coues 1873b , Bendire 1882b ). Between 1872 and 1886, the numbers of this species near Fort Lowell declined, and one last specimen was taken 7 February 1886 ( Phillips et al. 1964a ) before the species seemingly disappeared from Arizona until 1915. In 1932, however, specimens were taken near Sells, Arizona ( Moore 1932 ), and in 1936 a population was rediscovered near Tucson ( Phillips et al. 1964a ). The sparrow's preferred habitat of thornbush and mixed bunchgrass is limited; grazing appears to have diminished its numbers and distribution.
The plaintive whistled songs of the Rufous-winged Sparrow are distinctive and may be heard year-round, particularly during the breeding season. The nests of this species are easily found; they are usually placed conspicuously in a spiny tree or shrub, unlike the nests of other North American sparrows, which are hidden in grasses or low in shrubs. Of all North American birds, the Rufous-winged Sparrow may depend the most on rainfall as a stimulus for nesting. It typically nests after summer rains have begun, often building a nest and laying its first egg within 5 or 6 days after the first rain. Incubation lasts 11 days, and young fledge in only 8 or 9 days. In Arizona, in years of unusually heavy winter rainfall, pairs may also nest in spring. Territories are normally maintained throughout the year, and pairs remain mated for life.
Most natural history studies of the Rufous-winged Sparrow are from Arizona; little has been reported from Sonora, Mexico, the species' main center of distribution. Key studies of breeding biology are reported in Phillips et al. 1964a , Phillips 1968d , Austin and Ricklefs 1977 , and Wolf 1977 . Recent studies have focused on the breeding physiology of this dryland bird, especially its response to stress, to rains, and to the songs of conspecifics (e.g., Deviche et al. 2006, 2014; Small et al. 2007, 2008a, 2008b).