November 14, 2013

Bell's Sparrow

Bell's Sparrow

Sagebrush Sparrow

Sagebrush Sparrow

Even though it’s been close to four years since I “chased” a rarity somewhere in the country or even here in Arizona, I’m still a student of birdlife and I still completely understand the thrill of discovery.  It feels a little strange, then, to report that the new Life Bird I saw a couple weeks ago was one I had probably already seen.  Still, I was excited about seeing it again, differently now, through the lens of its recently explicated diagnosability.

Some of you may be aware that earlier this year the AOU (the birding “powers that be”) decided, on the basis of DNA studies, that Sage Sparrow should be “split” into two distinct species, one they called Bell’s Sparrow, the other Sagebrush Sparrow.  This split presents Valley birders an opportunity to test their observation skills and add a bird to their lists, if they are listers, all within an hour’s drive of home because both former subspecies of Sage Sparrow winter at the Salome Highway thrasher site and both molt into fresh plumage before they arrive there.

Splits are always accompanied by this conundrum:  if you have “probably” seen both subspecies before the split, do you need to see and identify them after the split to justify both being on your list?  Well, it’s your list, and I don’t think it will be part of the questionnaire at the Pearly Gates, but I thought it would be fun to see if I could actually find and then, to my own personal satisfaction, separate the much less common Bell’s from all the Sagebrushes running around the “thrasher site.”

Here is a condensed version, in descending order of reliability in the field, of the physical differences between Amphispiza belli belli (Bell’s) and A. b. nevadensis (Sagebrush), as I understand them from the homework I did prior to my trip out to Salome Highway:

1)  Bell’s shows much greater contrast between head and body color, dark gray over dark rich brown, than Sagebrush, light gray-brown overall.

2)  Bell’s has a thick, black malar (moustache) stripe darker than its head, Sagebrush a thinner, gray malar stripe that does not contrast with the color of its head.

3)  Bell’s mantle (upper back) stripes are absent or faintly visible, Sagebrush’s bold and obvious.

4)  Bell’s flanks are a rich, cinnamon brown whereas Sagebrush has only a suffusion of soft, light brown low on its sides.

5)  Bell’s bill is smaller than that of Sagebrush.

6)  Bell’s body is smaller with shorter wings than that of Sagebrush.

7)  Bell’s may show buff on its outer tail feathers, Sagebrush white.

Out at the thrasher site all the sparrows in the Sage complex, as well as the much sought Le Conte’s Thrashers, run around with their tails cocked up gleaning insect prey from beneath the gray-green Saltbush, seldom flying, even more rarely teeing up in plain sight for lengthy visual study.  This is probably one of the ultimate identification challenges in Arizona.  I spent six hours and felt I got photographic proof of two Bell’s amongst thirty or forty Sagebrushes, and I also had three Le Conte’s Thrashers.  The Le Conte’s are resident, but later in the winter might prove better for the sparrows as more arrive from the north.

If this all sounds too easy, keep in mind A. b. canescens runs with this crowd and is considered intermediate between Bell’s and Sagebrush, still officially part of the Sagebrush complex.  Canescens could be hybrids or may represent clinal progression from northeast to southwest on the breeding ground.  If you’re good with your ears, check out for sound recordings of all three.  If you’re confused or curious, join my Desert Rivers Audubon Society field trip to the area on Monday, February 3.  I’m the furthest thing from a sparrow expert, so we’ll all learn something together and that’s what birding should be all about.

Sagebrush Sparrow, A. b. canescens, intermediate between Bell's and Sagebrush
Sagebrush Sparrow, A. b. canescens, intermediate between Bell's and Sagebrush