Meet the Sagebrush Sparrow

In Wyoming, many birders have become familiar with the Sage Sparrow, which is a common sagebrush obligate species that breeds across much of the state.  However, the Sage Sparrow as we know it no longer exists.  In July 2013, the American Ornithologists' Union (AOU) published their annual supplement to the Check-list of North American Birds.  In this update, the AOU decided, based on extensive research, to split the Sage Sparrow into two species (Chesser et al. 2013).  The first, the Bell's Sparrow (Artemisiospiza belli), is found in chaparral dominated habitat in western California south to central Baja California.  It reaches east-central California, where it has limited contact with the second species (Cicero and Johnson 2007, Cicero and Koo 2012).  The second species, which is widely distributed through the Great Basin in sagebrush steppe, and is especially common through much of Wyoming, is the Sagebrush Sparrow (Artemisiospiza nevadensis).

Sagebrush Sparrow (Artemisiospiza nevadensis) - Albany Co.

The decision to split the Sage Sparrow into two species was based on genetic evidence, ecological data, and morphological differences between Bell's and Sagebrush Sparrow.  These two species come into contact in a narrow region of east-central California.  Where they meet, there is limited interbreeding, meaning each species prefers members of its own species, resulting in few hybrids and little gene flow (Cicero and Johnson 2007, Cicero and Koo 2012).  Further, there are strong niche differences between the two sparrows, with Sagebrush Sparrow preferring the cooler, wetter Great Basin desert sagebrush, and Bell's Sparrows favoring hotter, drier regions with less variability in temperature through the year (Cicero and Johnson 2007, Cicero and Koo 2012).

While this decision has relatively little impact on us here in Wyoming, it does add a new species of bird to the already diverse class, Aves.  It also means that the next time you're in California and see a Sage Sparrow, it is now recognized as a distinct, new species, the Bell's Sparrow.  This new research also adds to our understanding of how species boundaries are formed, and what factors may be important in the constant evolution of species.

Note: all photos in this post are © Shawn Billerman

References:

Chesser, RT, RC Banks, FK Barker, C Cicero, JL Dunn, AW Kratter, IJ Lovette, PC Rasmussen, JV Remsen, Jr., JD Rising, DF Stotz, and K Winker. 2013. Fifty-fourth supplement to the American Ornithologists' Union Check-list of North American Birds. The Auk 130(3): 1-14

Cicero, C and NK 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 27: 78-95

Cicero, C and MS Koo. 2012. The role of niche divergence and phenotypic adaptation in promoting lineage diversification in the Sage Sparrow (Artemisiospiza belli, Aves: Emberizidae). Biological Journal of the Linnean Society 107: 332-354