By Chet Meyers
Birding legend Roger Tory Peterson is credited with having coined the phrase confusing fall warblers in the third edition of his Field Guide to Birds, published in 1947. More than half a century later, many birders still hold to the notion that fall warblers are mystifying to identify. A birding friend of mine simply throws her hands up in the air and surrenders any thought of sorting out species in the waves of fall warblers.
That's too bad because, of the 33 species that regularly pass through Minnesota in fall, few are truly confusing. And with young birds boosting the number of migrating warblers, there are more individual birds to see.
What can make a fall warbler confusing to identify? These small birds— about 4 1/2 to 5 1/2 inches from bill to tail, the size of a black-capped chickadee—prefer heavy cover, such as thick brush or the canopy of oak trees. They are relatively easy to spot in early May when newly emerging leaves are smaller than the warblers. But in the fall, the mature leaves of oaks, maples, and basswood are bigger than the warblers. What's more, as fall leaves turn from green to yellow, they resemble the colors of warblers.
The identity confusion increases because plumage differences between males and females are more subtle than they were in spring. Many males no longer sport bright breeding plumage; their color patterns are more subdued. Fall females, like spring females, are often a paler reflection of the males. In addition, immature warblers join the fall migratory ranks. And they too sport plumage that is similar, but fainter, than that of adult males in the fall.
Again, the good news is that during fall migration warblers are often plentiful. And many species retain distinctive color patterns that aid in identifying them. Even novice birders can enjoy fall warblers, if they know when, where, and how to look for these colorful, sprightly bundles of feathers.
In Minnesota, fall warbler migration begins in early August and runs into mid-October. A few species fly to the far southern United States, but most head on to Mexico, Central America, Cuba, the Bahamas, and the West Indies for the winter.
Like many small songbirds, warblers usually migrate at night and often in large flocks. A clear night with a slight north wind can be a harbinger of prime warbler viewing the next morning. When the sun rises, warblers begin to recharge their batteries by foraging in trees for insect larva. Here are some tips for locating and identifying them:
Know where to look. During the spring breeding season, and also during fall migration, warblers prefer mature woods, such as healthy stands of oaks — the larger the woods, the better. Every state park or natural area with a bit of forest attracts warblers.
Birders often find warblers easier to see in clearings or along the edges of thick woods. Wooded lakeshores attract many warbler species. One of my favorite places is a path following railroad tracks that border a stand of woods.
Recheck likely spots. Warblers move in waves. That is, groups of mixed species move together — and they do move. Don't expect them to stay in one place for long. Be sure to recheck likely areas you visited earlier, because those that were devoid of birds an hour ago could be hopping with them the next time around.
Listen for chickadees. Chickadees often mix in with warblers during fall migration. Their excited, almost-constant chick-a-dee-dee-dee is usually a sure bet for finding warblers.
Pinpoint species. A bird's precise location in the woods can yield clues to its identity. Many warbler species feed in the upper canopy; a few forage on the ground. Northern waterthrush, ovenbird, and Connecticut warblers are classic ground foragers. If you see a bird foraging at about eye-level in a tree or shrub, it could be a black-throated blue warbler. Is it working along a branch or a tree trunk like a woodpecker does? That's most likely a black-and-white warbler.
Consider time of year. Different species follow a more or less orderly fall migration pattern. Yellow warblers begin moving south in early to mid-August. Other early migrants include blue-winged, Canada, and Wilson's warblers. If you see a warbler late in October, you're probably looking at a yellow-rumped, palm, or orange-crowned.
Look for telling colors. After spring breeding, most warblers molt. With their new feathers, they assume a generally drabber appearance. In some species, the male's fall color patterns are the same but not as striking as spring breeding plumage. For example, the Canada warbler's black-streaked necklace is simply a paler rendition of its bold spring garb. Likewise, its brilliant yellow chest and belly, gray-green back and wings, and distinctive white eye-ring take on more muted tones. Other birds with subtle color changes include Tennessee, black-throated green, and golden-winged warblers.
Males of three species — yellow-rumped, blackburnian, and chestnut-sided warblers — change color rather dramatically. For instance, the gaudy male chestnut-sided warbler retains his two distinctive yellow wing bars but loses his golden-yellow crown, black mask, and most of his handsome chestnut-colored flanks. Instead, he assumes a light-green back, pale-white breast, and white eye-ring.
Watch for habits. Habitual behavior offers clues to warbler identification. American redstarts always catch my eye because of their characteristic fluttering motion, as they tumble downward through tree limbs. The palm warbler has a habit of pumping its tail up and down as it feeds close to the ground. The chestnut-sided warbler cocks its tail upward like a house wren and tends to slightly droop its wings downward.
Listen for calls. Songs and call notes, or chips, are helpful means of identification too. Learning these sounds takes a good pair of ears and lots of practice, but just hearing a song or call can help you locate a bird. Because birds are not establishing territory or trying to attract mates in the fall, you are more likely to hear single chips than full-fledged songs.
Study a few. Roger Tory Peterson's Eastern Birds has two pages listing confusing fall warblers. For further study, I recommend Warblers of North America by Jon Dunn and Kimball Garrett. I think the really tough ones to distinguish are the blackpoll, bay-breasted, and pine. Blackpoll and bay-breasted males lose most of their spring markings, including their distinctive head coloration. As these two fade to drab fall dress, they begin to resemble the pine warbler, which changes little. But despair not. Even these three can be identified with a little practice. In the fall all three have white wing bars and olive-green to green-yellow crowns and backs. Bay-breasted and blackpoll usually have dark streaks on the back. Pine warblers have no streaking on their backs. Many bay-breasted warblers retain a hint of bay coloring on their sides.
If the confusing warbler has pink or pale yellow-orange legs, it's almost surely a blackpoll because pine and bay-breasted warblers seldom, if ever, have pink or yellow legs. More tellingly, blackpolls move much more slowly and deliberately while feeding. If a wave of warblers passes through, a lone blackpoll may be the last to leave.
Get on it. One frustration to warbler birding is catching sight of these active little birds with binoculars, or what birders call "getting on the bird." The best advice: Use 8-power binoculars with a large field of vision, at least 8 x 40. First spot the bird with your bare eyes. Then, hold your head still and lift the binoculars to your eyes. Hold your binoculars steady (don't tip them) and move them with your head, as if they were an attached pair of glasses. Sounds simple, but it takes a little practice.
One fine fall morning 20 years ago, I left home for a nearby woods and told my wife, "I'm finally going to tackle those darn fall warblers, so don't expect me back any time soon."
Later, as I was craning my neck toward a confusing warbler, a fellow birder asked, "Whatcha looking at?"
"I don't know," I said, as I tried to match the bird's plumage with one in my guidebook. "Well, what's it doing?" he said.
I responded, "Well it's definitely a warbler and it's working along this branch with its tail cocked up and sort of droopy wings."
"Yep!" my new birding friend replied. "That's just how a chestnut-sided warbler acts."
He was Don Bolduc, one of Minnesota's finest birders. From him, I learned that birding is not just about matching living birds to pictures. It's about understanding the total bird — seasonal color patterns, behavior, songs, habitat, and timing of migration.
By patiently studying these facets of warblers, any birder can be well on the way to sorting out these delightful winged visitors as they pass through in waves every fall.
Chet Meyers teaches at Metropolitan State University and is an avid birder, angler, and wildflower gardener.