Winter vs. Pacific Wren vocalizations
In just a few months it'll be Winter Wren season again for those of us who live in mid-latitudes and low elevations (i.e. not the breeding grounds). As most birders already know, this formerly cosmopolitan species has just been split into three species: Pacific Wren, Winter Wren, and Eurasian Wren. The first two of these occur in North America, of course. The breeding ranges of the two American species are well-known; however their wintering ranges are much more uncertain. There are broad areas across the central and western U.S. where either or both species might be expected; the eastern extent of the wintering range of Pacific Wren is very poorly known at this point. This winter will be a biggie as we start to sort this out.
Most birders also already know that the primary visual mark to separate these species is the throat color (rusty red for Pacific, mousy brown for Winter). But the throat color on Winter Wrens is actually rather variable and often hard to judge in shady forest understories. As you get farther east, the "bar" for calling a Pacific Wren gets higher. There's a photo of a bird from western Tennessee (Moss Island, actually) from 2009 that shows a "Winter"-type Wren with a quite rusty throat. Is this a Pacific Wren?
My opinion is that to identify this species in Tennessee or any other eastern State without a specimen you will need to use vocalizations as a critical characteristic. We may eventually find out that the Pacific is a regular bird in some areas east of the Rockies; but until then we need to treat it as a State-level rarity. Even where both species are common, these are some of those birds that prefer to be heard and not seen, so vocalizations are definitely the easy way to go.
Fortunately, the calls of the two species are distinctly different. The typical call of both is a sharp chip, often (but not always) doubled as if to say "Win-Ter, Win-Ter, Win-Ter." A good sample of an eastern Winter Wren (from Ontario) is here:
The quality of the call of the eastern bird is rather similar to the chip of a Song Sparrow; in fact I think it often gets overlooked because of this, judging from the huge variability between different birders in their Winter Wren totals on Christmas Bird Counts in the southeastern U.S. The doubling of the note is characteristic, though, and usually lets you tell the wren from the sparrow.
Here is a typical sample of the corresponding call from the Pacific Wren (recorded in Oregon):
The pattern is the same, but the quality is much different. It is drier and harder. Western birders liken it to the chip of a Wilson's Warbler; a sound they hear far more often than we Easterners do! Still, the warbler-like quality is quite different from the call of the eastern species, and is diagnostic.
Of course, until we know the true status of the Pacific Wren in many eastern regions you will really need to both see AND hear the bird to nail the identification; the same is true for Winter Wrens in parts of the West. I also think that, barring any specimens turning up in existing museum collections, we should get some audio recordings to document the Pacific Wren in the eastern States before thinking of adding it to any State lists. Fortunately both species are quite vocal and responsive to spishing, so that should not be too great a challenge. Even small handheld camcorders can record audio adequate for this purpose.
And, of course, after you carefully sort out the species of your "Winter" Wrens, be sure to enter the data in eBird so that we can ALL watch the emerging picture develop. The species-level split has not yet been implemented there (but likely will be before the winter birding season starts); in the meantime you can use the options for 'Winter Wren (eastern)" and "Winter Wren (western)" and they will get correctly reassigned to the species when the split is put in force.
Just some wintery thoughts during a stubborn heat wave...