Tuesday, September 9, 2014

Large-billed Savannah Sparrow

Large-billed Savannah Sparrow
Large-billed Savannah Sparrow. San Luis Rey River Mouth, Oceanside, California. September 7, 2014. Greg Gillson.
While looking at shorebirds at high tide at the San Luis Rey River mouth I noted additional shorebirds in the beach-cast seaweed between the river and the ocean. (The river doesn't quite reach the ocean as the beach blocks the river mouth with sand.) Also, a small bird was running around chasing flies among the piles of seaweed. It was pale and plain brown above--barely showing a few streaks on the back, heavily streaked below. It had a pale eyebrow and submustachial stripe, both bordered with darker brown. The way it was behaving reminded me of a pipit--but the tail was also pale, not black with white outer tail feathers as in pipits.

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.

Large-billed Savannah Sparrow

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.