Birdist Rule #41: Identify Your First Warbler

Spring migration is a birder’s Christmas Morning. It’s a birder’s Happy Hour after work on a Friday. It’s a birder’s Embrace with Loved Ones in the Airport After a Long Journey. The wait is over and we can stop pretending we actually enjoy standing in the freezing wind looking at gulls. As you read this, millions of birds are winging their little bodies north from the tropics, and for many American birders, the most yearned-for of these birds are the warblers.

Warblers are the gems of American birdlife. Unlike warblers in the rest of the world, which are mostly brown and boring-looking (and not actually closely related to our local birds), our New World warblers, or wood warblers, are tiny bursts of color. Bright yellows! Oranges! Greens and blues! Each of the 50-or-so species regularly found in the U.S. has its own color scheme, vivid and delicately patterned, like a fluttering Easter egg.  

They’ve been away because they’re insect eaters, and the States aren’t really where you want to be if you’re looking for insects in December. Some warblers will spend the winter in the southern U.S., but most will be farther south, in Mexico and Central America, the Caribbean, or even South America.  Then, over the course of just a couple weeks, they flood back, some species headed as far as northern Canada.

Will you be ready?

Warblers are a daunting group.  All those different colors and patterns mean there are a lot of details to keep straight when trying to make an identification. Complicating things, males and females frequently have different plumage. Oh, and also they’re just impossible to get a good look at—they’re small, they move around a lot, and seem to be always either far away at the top of a tree or back in the shadowy understory.

I remember cracking my field guide open to the warbler pages the night before my first big spring migration day, at Ontario’s famous Point Pelee, and panicking. (I’m not very good at planning ahead.) How am I supposed to remember all this? The answer on that crowded day in May was: “Stand next to someone who is good at identifying birds and nod your head in agreement at everything they say.” It worked for me (I got 30 lifers that day!), but you might not be so lucky as to be at one of the continent’s most famous birding spots, surrounded by birders. But you’ve got to start somewhere.

The first step to identifying warblers is to begin with an easy one. Let’s learn a Yellow-rumped Warbler.

Yellow-rumps are a good starter warbler for a couple of reasons. First of all, they come early, and there are a lot of them. They’re hardy, able to spend winters much farther north than their kin, and since they’re not that far away to start with, they’re among the first to show up at their breeding grounds in the Rocky Mountains, New England, and Canada. Check out this chart I made using eBird data, showing Yellow-rumped Warbler arrival dates and abundance compared with two other warblers, the Cape May Warbler and the American Redstart. Notice that Yellow-rumps really start showing up in big numbers about the second week of April, about two weeks before the others. The trees are flooded with Yellow-rumped Warblers in mid-April, letting you get a good look before all the others arrive.

Then all you really need to remember is that the people who named bird species were not that creative. The most distinctive feature of the Yellow-rumped Warbler is, believe it or not, its yellow rump. Young and non-breeding birds are brown and grayish overall, and breeding males are slaty blue, with a black mask, but they’ve all got that yellow butt. Though it’s fainter in the fall  and winter, it’s a distinctive caboose that can be seen on both males and females, any time of year, shining from the rear end like some kind of avian Coppertone baby.

Also helpful for identification are the yellow patches on the part of the warblers’ body that most guides refer to as their “sides,” but which I always think of as their “armpits” (wingpits?).  These patches can be sort of faint in non-breeding birds, but they’re always there, and, in combination with the rump patch, are a sure identification tip.

Once you’ve seen the rump and the armpits, check the throat. Here’s where it gets interesting. There are two forms of Yellow-rumped Warblers in the States, the eastern “Myrtle” form and the western “Audubon’s” form. It’s believed that the most recent ice age split the population in two, and taxonomists have been trying to work things out ever since—for now both forms are considered part of one Yellow-rumped Warbler species, but at one point they were considered separate species, and they may be considered that way again. For our purposes, all you need to know is that the Audubon’s form has a yellow throat and the Myrtle form does not; if you see a yellow-throated bird on the east coast, that’s a rare treat, and the same goes for white-throated birds out west.

Once you’ve got the relatively easy identification down you’ll enjoy watching these Yellow-rumps flit around in the trees. They’re fairly social birds, especially in winter, and it’s not uncommon to see groups of twenty or more be-bopping through the branches, looking for insects. They may not be the rarest warbler, nor the most colorful, but they’re one of the surest signs that yes, finally, spring migration is on its way.