|Large-billed Savannah Sparrow. San Luis Rey River Mouth, Oceanside, California. September 7, 2014. Greg Gillson.|
It was soon apparent by its rather large conical bill that it was a sparrow--looking very much like a pale Song Sparrow. But it lacked Song Sparrow's very heavily streaked back, and the facial stripes weren't quite right. I then knew what it was: Large-billed Sparrow, a primarily Mexican race of Savannah Sparrow. It differs from other Savannah Sparrows in generally lacking the yellow lores that help beginners recognize Savannah Sparrows.
In 2009 there was a proposal before the checklist committee of the American Ornithologists' Union to split Savannah Sparrow into 3 or 4 species: 1) the main North American group of Savannah Sparrows, 2) Belding's of the salt marshes of southern California, 3) Large-billed Sparrows of coastal NW Mexico, and 4) San Benito Sparrow of an island off the coast of Baja.
DNA evidence actually groups Belding's and Large-billed. At first this may seem strange. Belding's, after all, is quite dark and Large-billed pale. But both are birds of salt marshes and both have rather large bills compared to other races. At any rate, the proposal to the AOU didn't pass. They wanted more studies on Belding's from north of San Francisco and more study of the San Benito form. Future research may answer the gaps in knowledge, so a split could come one day soon--if nothing else, splitting the Belding's/Large-billed group from the main Savannah Sparrows.
See my previous post on Belding's Savannah Sparrows, that also pictures a western form of the main continental Savannah Sparrow.