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ALWAYS IN SEASON/ MIKE JACOBS: Fall delivers confusing warblers

Illustration by Mike Jacobs1 / 2
Mike Jacobs2 / 2

The Nashville warbler belongs to a group that birders call "confusing fall warblers." It is not the worst of the bunch, so getting to know the Nashville warbler is a way to break the code cloaking fall warblers.

We'll do that, after this little digression.

To begin with, the Nashville warbler has little to do with the city of Nashville. Its summer range is well to the north of the country music capital, and its winter range is in Mexico, well to the south. Naturalist Alexander Wilson encountered the bird near Nashville, on its way between summer and winter homes, and named it for the city. This is just one example of misleading names of warblers. The palm warbler, for example, is common in our area both spring and fall, while the prairie warbler never ventures this far north.

The names are easy enough to keep straight. It's their appearance that causes confusion.

In spring plumage, many warblers are among the brightest in the bird world. Candor compels this admission, however. They are challenging, not only because many are quite similar but because all of them are small enough to disappear behind tree leaves or grass clumps.

Adding to the challenge, warblers don't tarry here. Only two species are common breeders locally—yellow warbler and common yellowthroat—though the breeding bird list includes four other warbler species. The list of migrant warblers is much longer — about two dozen species — but the window to see and identify them is narrow. What's more, the window doesn't open in some years because the warblers just blow by; not quite literally, perhaps, although warblers and weather do go together.

Birds often move ahead of weather systems. Advancing high pressure helps the birds; a persistent low pressure system stops them. Sometimes, this produces what is known as a "fall." The term is apt because the birds seem to have dropped out of the sky. Such a warbler fall in spring can deliver sightings of species that otherwise would bypass the area. In the fall months, a low pressure system can delay the birds. This causes frustration for birders; although the warblers are easy to see, they are hard to identify, hence the phrase "confusing fall warblers."

A significant low pressure system settled over our area last week. Our place west of Gilby, N.D., was at the edge of this weather phenomenon and north of the heavy weather. While we were cheated of rain, we were treated to warblers — of the confusing kind.

There were several of them flitting about in an evergreen shrub not far off the ground. These were active birds, but they were not conspicuous. Drab doesn't quite describe them. Subtle is a better word, I think. Overall, they were grayish green, perhaps grayer at the front and greener at the back. On the belly, they were yellow.

This general description fits at least a half dozen warbler species that might occur here in early fall: Wilson's orange-crowned, Tennessee, bay-breasted, blackpoll, Connecticut and Nashville.

The birds in my backyard had no wing bars, not even a hint of them. This eliminates the blackpoll and bay-breasted warblers. They each have a prominent and complete white ring around the eyes. This eliminates several other species, leaving only the Connecticut, which also has the eye ring. The Connecticut is among the larger warblers; David Crossley calls it "pot-bellied" in his Crossley Guide. Also, it is generally pale yellow on the breast.

Through elimination, this leads to identification: Nashville warbler.

Nashville warblers nest nearby. The Manitoba Naturalists' Association suggests that Nashville warblers reach their highest nesting density in southeastern Manitoba and adjacent areas of Ontario and Minnesota. That's not far from Grand Forks. Their summer range extends to central Saskatchewan, well to the northwest, the direction from which the wind reaches our area. Nashville warblers have been spotted in the Turtle Mountains and the Pembina River gorge, both tight against the Canadian border.

Nashville warblers are regular migrants here, and not surprisingly, they are more numerous in the fall, when the population is swollen with young-of-the-year birds. I've missed the birds some years; that probably has something to do with the weather and something to do with my own birding effort.

That's why I was delighted to find — and identify — Nashville warblers last week. Of course, I didn't remember all of these field marks. I noted them and consulted the field guide.

That's not cheating.