To start this discussion of a thorny issue, let me say that I am far from any sort of "expert" on the subject of Sagebrush vs. canescens Bell's Sparrows. I do not have any magic answers. And I do NOT wish to suggest that any particular sparrow report is in error–but rather, that the overall situation is likely murkier than perhaps some observers believe. Over the past many months and couple years, a fair number of folks have been reporting numbers of Sagebrush Sparrows from a variety of sites in the Anza-Borrego area in eastern San Diego County. It is extremely likely that some (a few? some? most? almost all?) are correctly identified. But it has struck a number of us that PERHAPS a fair percent of observers are also separating and reporting Sagebrush vs. canescens Bell's Sparrows a bit too nonchalantly (?). This is NOT a straightforward identification. Well, at least some observers think it is not so "easy" as some others have been led to believe. The desert form of Bell's Sparrow–canescens–is, of course, somewhat intermediate in many key features between the more obvious separation of nominate Bell's Sparrow from Sagebrush Sparrow. Following the taxonomic split just a few years ago, there were several postings, on-line sites, and perhaps publications which discussed the separation of these "new" species, and a number of us think that some of those presentations might have made the situation seem more clean-cut and straightforward than it really is. But I am sure there is disagreement even on that score, as some folks do think the two "species" are straightforward most of the time; whereas others think the situation is decidedly more muddied, with perhaps just the two end-point extremes of the "plumage continuum" being readily ID'd in the field, but with a lot of muddy gray-zone in the middle; and then there are even at least a couple very knowledgeable museum ornithologists who say that, based on an analysis of specimens in the hand, there is too much overlap in many key characters as to make confidently IDing many birds in the field impossible. Many of the eBird reports of Sagebrush Sparrows from Anza-Borrego are accompanied by the best details allowable under the circumstances and/or are accompanied by a very helpful SERIES of good photographs, whereas some others are pretty minimal, with only a few mediocre photos or no photos at all and only some brief, cursory written details covering only a limited number of field characters (e.g., back streaking, malar boldness). In many cases, such brief written details are simply not detailed enough to allow for proper review by eBird reviewers and others. I know that there is more than one frustrated eBird reviewer out there (not me!), frustrated by the limited details that make any sort of meaningful review virtually impossible.
A fair number of observers reporting Sagebrush Sparrows will write that a bird had distinct back streaking and not a distinct dark malar-stripe. Burt this is not enough. In fact, canescens Bell's Sparrows often have very distinct dark back streaking on the entire sides of the back (totaling well over 50 percent of the back area), and it is only right in the middle of the back that these streaks get weaker or disappear completely. And a very large percent of canescens Bell's totally lack the upper half of what would be a complete dark malar-stripe, but do have a lower-half malar that is distinct (quite dark and not too thin). Also, there may or may not be an important habitat preference that might shed some light on some reports of Sagebrush Sparrow in the county. Sagebrush Sparrow may well prefer the most semi-barren desert areas characterized by saltbush (Atriplex), creosote, and related veg at places like "Dump Road," or well away from the sewage ponds, or at Clark Dry Lake. In other words, think LeConte's Thrasher! And canescens Bell's is found there as well. But once one enters slightly more "lush" habitat of mesquite–such as immediately bordering the old sewage ponds, or out in much of the Borrego Sink, or in the fringing desert veg right near many of the hotel-resorts in Borrego Springs and vic.–then almost all the sparrows are canescens Bell's.
So, what to do?? I think it would be good for us to take one step BACKWARD in reporting these two taxa to species in San Diego County, and report only those that are seen very, very well (as best as can be done with these shy, fast-running birds!!!!!) and try to obtain a series of good photographs; but be willing and happy to leave many of them identified only as canescens Bell's/Sagebrush. Most of us have NOT spent lots of time in the desert Southwest over the years closely studying LARGE numbers of Bell's and Sagebrush Sparrows. I certainly haven't. So, how many of us really know the variation possible in these taxa? A few people have done so, including a detailed banding-study in sw. Arizona a couple years ago (which we could now use in se. CA !!!), but very few. Also, please carefully note your location and the dominant desert vegetation (atriplex/creosote vs. mesquite vs. ??) when you submit your reports. In many, but not all, areas in the Borrego region, canescens Bell's is likely the default "Sage" Sparrow. But that should not be used to make an ID, and, as mentioned earlier, the use of slash Bell's/Sagebrush is encouraged in many instances.
Lastly, please do NOT send me any of your photos to identify! :-) As I said at the beginning, I am no expert on this species pair. Like lots of people, I am fumbling around with a fair percent of the birds I see (or photographs I see) out at Anze-Borrego and elsewhere in se. California. And it doesn't help that these little buggers often don't sit still!
–Paul Lehman, San Diego
Source: SanDiegoRegionBirding Latest Reports