Focus On...Black-throated and Sage Sparrows
The Black-throated Sparrow is one of the most typical species of the Anza-Borrego Desert. It is especially common on alluvial slopes well vegetated with Teddy Bear Cholla--one of the favorite sites for its nest. Because of protection such a site affords, the nests are often not well concealed, making the Black-throated Sparrow one of the best candidates for application of the isolated-thorny-shrub principle. The species' numbers are much lower on the flats and in the badlands, but even there a few can be found. It ranges up into the piñon/juniper zone of the Vallecito Mountains (squares K25 and K26) and as far up the east slopes of the mountains as thickets of cactus and catclaw extend, as shown by the observations of Brian Bothner in Alder Canyon (C21) and Dave and Cyndee Batzler in Oriflamme Canyon (M22). In the San Felipe Valley it ranges west in juniper scrub to square J21; the species' extension up the east slope of the valley into H21 and I21 hasn't yet been captured by our atlas effort.
The Black-throated Sparrows breeding in San Diego County are probably sedentary, and this is reflected in the winter distribution's closely matching the breeding distribution. Those breeding to the north in the Great Basin, however, are somewhat migratory, and these are most likely the source of the occasional vagrants that reach the coast in the fall. These vagrants are almost always in the white-throated juvenile plumage, the same plumage that resembles the Sage Sparrow.
Our results so far reveal the Sage Sparrow to be most widespread in south-central San Diego County, where an extensive plateau is still covered with vast tracts of chamise and redshanks. Toward the northwest, where the chaparral is often denser and more diverse, the distribution becomes patchier, though as the project evolves we should find the species in more and more places. The Sage Sparrow's prime habitat is one often overlooked by birders, so please don't neglect uniform stands of chaparral if they occur in your square. If you have significant stands of sage scrub, of course, these are critical to cover well for several species as well as the Sage Sparrow.
Unlike many other chaparral and sage scrub birds, the Sage Sparrow has little or no ability to survive in isolated patches surrounded by urban development. In sharp contrast to such species as the California Gnatcatcher, the California Thrasher, and even the Cactus Wren, we have no records of the Sage Sparrow from isolated canyons enclosed within the city of San Diego--a bad sign for the sparrows persisting in the San Marcos (I9, J8) and Poway (M10, M11) regions. The most extensive population remaining near the coast is that on Marine Corps Air Station Miramar (O10, O11, P10), where the Sage Sparrow lives among the vernal pools. How large a tract of chaparral or sage scrub is needed to support a viable population? The Sage Sparrow looks like a far more sensitive indicator species than the California Gnatcatcher.
Our collection at the San Diego Natural History Museum suggests that in their winter range nevadensis and canescens mix indiscriminately but both prefer a distinctive habitat: desert floors vegetated sparsely with salt-tolerant shrubs, typically saltbushes (Atriplex) and iodine bush (Allenrolfea). Correspondingly, our atlas results show wintering Sage Sparrows in desert sinks: Clark Dry Lake (D26, E26), Borrego Sink (F25, G25), and Halfhill Dry Lake (J29). The species is not restricted to these habitats, however; the atlas effort has revealed it in badlands, in washes, and on gentle alluvial slopes as well.
Subspecies nevadensis and canescens are known in eastern San Diego from October through March. It is plausible that in a cool, wet year that canescens could linger and breed south of its normal breeding range, which extends to the north base of the San Bernardino Mountains. But my following up on a few reports of the Sage Sparrow in the Anza-Borrego Desert in April and May revealed some uncertainty among the observers over how the juvenile plumage of the Black-throated Sparrow differs, so I converted any such report of a Sage Sparrow to a juvenile Black-throated. Some useful differences: The Sage has a blackish malar stripe outlining a white stripe below the gray cheek, the juvenile Black-throated does not. Only the sides of the breast of the Sage are lightly streaked, leaving the dark breast spot isolated on a nearly white breast; the juvenile Black-throated is rather uniformly striped over the whole breast, with no central spot (unless the black throat is beginning to grow in). The juvenile Black-throated has the same tail pattern as the adult: a sharply contrasting white patch on the inner web of the outer rectrix. The pale areas on the outer rectrix of the Sage Sparrow are clouded with brown and not conspicuous in the field.
Unitt, with sketches by Nicole Perretta, from the fall 1998 issue of WRENDERINGS
about the Sage Sparrow