Friday, January 29, 2010

Oriantha White-crowned Sparrows – on the move?

I digiscoped this White-crowned Sparrow from my office/bedroom window this afternoon. I was pretty intrigued by it. Most people wouldn't have paid much attention to this common wintering bird here. After all, the Tucson Valley Christmas Bird Count tallied 793 of them, and the Atascosa Highlands Christmas Bird Count had 651: it's not a rare bird. But this one is quite different that the five or so individuals that have been wintering in my yard this winter. I've been watching them, along with the single Abert's Towhee, two Violet-crowned Hummingbirds, and others in my medium-sized urban backyard.

Notice the prominence of the white stripes, the pattern in the face in front of the eye, and the bill color. This is a "Mountain" White-crowned Sparrow, also knows by the trinomial Zonotrichia leucophrys oriantha. Compared to other western North American subspecies, there is an extra little bit of black above and in front of the eye separating the white stripe over the eye from the the gray lores between the eye and the bill. Those white stripes are also broader, more striking. The bill is redder than the other yellow-billed forms. Compare it to this Z. o. pugetensis from Oregon (rather similar to our more common Z. o. gambellii) with its white supercilium continuous with the gray lores and yellow bill.

There are two very distinctive features of the the Mountain White-crowned Sparrow that are not visible from photos – or from specimens. The latter source of information (specimens) is where we got our master list of species of birds known from North America. It wasn't handed down by God, and so includes some errors – many of which still remain to be corrected.

First of all, we now know that Mountain White-crowned Sparrows have a radically different biogeography from other forms of White-crowned Sparrow. The biogeography includes their breeding range and habitat, migration route, migration timing, and wintering grounds and habitat. This is most evident here in southern Arizona in winter and spring: our common winter birds are virtually all Gambel's White-crowns, which depart for their breeding grounds in early April. Then suddenly in late April into mid-May there is another push of White-crowns, and they are all Z. l. oriantha then. They obviously winter south of here and migrate to their breeding grounds later. There are exceptions: one Mountain White-crowned Sparrow was identified on the Atascosa Highlands CBC, and in the winter of 1999-2000, an unprecented number of them wintered in southern Arizona (see that issue of North American Birds, which you can find at the Searchable Ornithological Research Archive [SORA]). These birds breed in the Intermountain West of North America. Gambell's White-crowns, in contrast, breed near edges of boreal forest of Arctic Canada and Alaska.

The other notable characteristic of Mountain White-crowned Sparrows that early ornithologists overlooked is their amazingly distinctive song. The example that was meant to be included on the CD set Bird Songs of the Pacific Northwest by Geoffrey A. Keller and Gerrit Vyn can be heard on the Cornell Lab of Ornithology's Macaulay Library website, catalog number 42273. (Incidentally, somehow the editors accidentally included catalog number 43976 on the CD instead, which is a White-crowned Sparrow from near coastal Charleston, Oregon that apparently learned an aberrant song through mimicry of either House Wren or House Finch; that particular cut is mislabeled in the CD booklet.) The fifth cut on the same CD set (also heard at the Maculay Library website, catalog number 130914) is what Gambel's White-crowned Sparrow sounds like – both in Alaska west of Fairbanks (where the CD bird was recorded) and here in Arizona where they winter.

It's only a matter of time before the American Ornithologists Union fixes this part of our checklist. It seems pretty clear to me that the form given the trinomial Zonotrichia leucophrys oriantha should actually be recognized as the unique species Zonotrichia oriantha.

1 comment:

  1. Nice find Rich. There has been one wintering at Tohono Chul Park too this winter. It hangs out under the feeder near the entrance. Haven't seen any anywhere else though and can't recall ever seeing one in winter before.