In 2010, the Sage Sparrow was classified as a species of conservation concern within Nevada. In the latest changes to the AOU (American Ornithologists’ Union) Checklist, the Sage Sparrow has been split into two species, the Bell’s Sparrow and the Sagebrush Sparrow. Both of these species breed within Nevada. The Sagebrush Sparrow (Artemisiospiza nevadensis) is far more common within the state, and found through much of the Great Basin, predominantly within sagebrush, but also within greasewood community types. A typical example of the Sagebrush Sparrow’s breeding habitat can be seen in the header photo at the top of this page – I heard several territorial males singing within this stand of sagebrush, and one individual was carrying food.
The desert race of the Bell’s Sparrow (Artemisiospiza belli ssp. canescens) is also found breeding in southern and western Nevada, where we have found it primarily within relatively dense stands of Atriplex (saltbush), though it can also be found in sagebrush within its range. Note that most maps I’ve seen showing the breeding range of the (canescens) Bell’s Sparrow do not include its range within southern Nevada. However, we have confirmed them breeding within salt desert both east and west of the Spring Mountains. Their range continues northward along the western edge of the state, towards Bishop. Below is an example of Bell’s Sparrow breeding habitat near the Spring Range in Clark County – within 50m of this location, I watched an adult Bell’s Sparrow feeding a fledgling. 
In 2007, Carla Cicero and Ned Johnson documented a zone of contact between the 2 species in the Owens Valley, near Bishop [1]. Walter Szeliga provided a useful discussion on Nathan Pieplow's earbirding.com of the differentiation between the former subspecies of the Sage Sparrow, including a map from Cicero (2010) showing the known range of the Bell’s Sparrow (ssp. belli), Bell’s Sparrow (ssp. canescens), and Sagebrush Sparrow. The map is useful for Nevadans in approximating the extent of the Sagebrush Sparrow, but does miss the Bell’s Sparrows breeding in the southern portions of the state. In the end, Szeliga concludes that the canescens subspecies’ song appears confusingly intermediate between the belli song and the Sagebrush Sparrow’s song, but speculates that some of this confusion may be due to clinal differences in song, or perhaps incorrectly identified examples. Personally, I haven’t surveyed the canescens subspecies of the Bell’s Sparrow where it nears its contact zone in Bishop, but the breeding individuals I have heard singing in Clark County have sounded quite different than Sagebrush Sparrows, with a song that seems shorter, flatter, and less musical.
During winter and migration, we have both species in southern Nevada, and absent song or a good look, differentiating between them is a tad difficult.
Happy birding-- and stay tuned!
Jen
[1] Cicero, Carla, and Ned K Johnson. 2007. Narrow contact of Desert Sage Sparrows (Amphispiza Belli Nevadensis and A.B. Canescens) in Owens Valley, Eastern California: Evidence from Mitochondrial DNA, Morphology, and GIS-Based Niche Models. Ornithological Monographs 63: 78-95.
