Fall Yellow Palm Warblers
(This column was first published in the December 17, 2001 Buffalo News.)
The call came from Don Roberson: "Gerry, I'm phoning because you wrote the account for palm warbler for Bull's Birds of New York State. This fall I have been seeing the 'wrong' subspecies -- the yellowish eastern race. They're rare here in western New York in fall. We normally see only the whiter subspecies and I'm worried about my reports being rejected by B.O.S. statisticians. Have you heard of similar reports?" (Don's B.O.S. referred, of course, to the Buffalo Ornithological Society.)
I thought that I remembered some e-mail reports about this from nearby Canada and promised Don that I would look into the matter.
First some background. The palm warbler is another of my favorite birds. Not as colorful as many other warblers, it is just as dainty. Its breast is lightly streaked and in spring it sports a chestnut crown. But plumage for this bird is not nearly as important for identification as is its habit of almost constant, perky tail-wagging. (Waterthrushes are also tail-waggers, but they usually occur in different habitat.)
Several decades ago two easily distinguished species were combined into today's palm warbler. In my section on those downgraded palm warbler subspecies in the state book I wrote: "The yellower subspecies...(formerly called the yellow palm warbler), breeds from eastern Ontario to northeastern New England and is the commoner migrant through eastern portions of New York.... The whiter, nominate subspecies...(formerly western palm warbler), breeds from northern Michigan west to the Rockies but migrates eastward through western New York and even to Long Island. Clearly they overlap in New York in both spring and fall. They also intergrade, thus further confusing subspecific identification."
Locally Beardslee and Mitchell's Birds of the Niagara Frontier Region describes the "yellow" palm warbler as "a fairly common migrant along the eastern seaboard, [but] of rare occurrence this far from the coast."
Most autumns we don't see "yellows" but this year Don was not alone.
A check with nearby Ontario birders brought several informative replies. Alan Wormington reported; "Prior to this year, there were only two fall records of 'yellow' palm warbler for Point Pelee. This fall alone there were eleven! In fact, late in October we saw five in one day, yet not a single 'western' palm warbler."
Jean Iron in Toronto referred me to an article by Ron Pittaway that cites some reports of "yellows" and she added, "We know that they are rare but regular and we look for them." She had seen one herself.
Fred Urie noted 14 "yellows" in Ontario and offered speculations about this unusual year: His own guess is that a series of low pressure systems moved through southern Ontario during October: "At the northern edge of these intense lows the counter-clockwise flow sucked 'yellow' palms out of Quebec, and moved them westward into Ontario." Another hypothesis, this one Fred passed on from Sarah Rupert, is that a severe drought "existed in northern Ontario this summer. If it extended into Quebec, bogs would have dried out and palm warblers may have dispersed into other areas...." His other two guesses are less scientific. "'Yellows' were always present in small numbers but were undetected due to low human coverage." And finally, their presence this fall was simply "a fluke."
I find this episode interesting not just because I have written about this species. There are not many bird subspecies that are distinguishable within this region. "Northern" and "prairie" horned larks are the only others that come to mind. Noticing more about birds that don't "count" on lists I believe is a worthwhile activity.
In any case Don's unusual identifications were almost certainly correct.-- Gerry Rising