Pine warbler Credit: Courtesy of Bob Duchesne

Here’s a birding game you can play at home. Identify the trill.

Trills are defined as a rapid alternation between two musical notes. Whenever a symphony imitates a bird, it’s always the flute player who gets to “trill.” Think of the bird in Prokofiev’s Peter and the Wolf. Or, for simplicity, think of a police whistle. Only a few birds trill. In Maine, there are four: pine warbler, chipping sparrow, dark-eyed junco and swamp sparrow. If you hear a trill, it’s one of these.

One of four: that’s good news. Up to 300 birds make noise during a Maine summer. Learning to identify them all by ear is daunting. But learning four? That ought to be easy, right? Except that they sound very much alike. Fortunately, all four trillers sing in April, before May when all of those other confusing songbirds flood back into the state. If ever there was a time to learn trills, this is it.

It’s likely you’ve got a triller around your own backyard. I’ve got two that I can hear from my porch right now, another that sang in my yard last week and a fourth that’s just down the road. All four birds are common in Maine.

Although the trillers sound alike, there are some distinctions to help you remember them. To get started, step outside and listen for a trill. Find the bird. It’s one of the four. That’s now your “default” bird. Get to know it. The other three are going to sound similar, but slightly different. You’ll be listening for a triller that doesn’t sound quite like your default triller.

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My default triller is a pine warbler. It nests above my house and stays noisy through June. Of the four, it’s the sweetest sounding, meaning that it has a clear, non-raspy musical tone. It’s easy to contrast with the other triller in my yard, a chipping sparrow. The chipper song is buzzier. It’s more metallic sounding, almost insect-like. It’s also a longer trill than the quick pine warbler.

Dark-eyed juncos are widespread, but they are less apt to be trilling in a suburban neighborhood. Although they are common under home bird feeders in winter, they tend to melt into the Maine woods during breeding season. They have a two-tone trill, like the ring of an old-fashioned telephone.

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Swamp sparrows have a sweet trill. It’s slower than the other three. Sometimes, it’s so slow it sounds like a series of individual notes.

Here’s another trick to help you learn the four trillers. They behave differently. Pine warblers reside in big stands of pine. They sing among the needles, seldom anywhere else. Even though they are bright yellow, they can be well-hidden in the foliage, especially since they tend to be moving around when they sing. When you can’t see the bird, and the trill comes from a pine, suspect this guy.

Chipping sparrows like open areas. They hang around city parks, suburban neighborhoods and college campuses. Most of the ones in my neighborhood are singing above driveways. They can be found at the edge of woods, but not in the woods. They tend to sing from open bare branches, lower in the canopy, where they are easy to see.

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Dark-eyed juncos tend to sing from open branches high in the treetops. Usually, they will sit in one spot to sing for a while, making them relatively easy to spot. Although they are most comfortable in forests with plenty of conifers, they can be found throughout the state.

Swamp sparrows sing from wetlands, where the other three trillers would never, ever go. They tend to sing from the tops of reeds and cattails, and from the bare branches of small bushes in the marsh. They are seldom much higher than eye level. If a trill comes from a low bush in a wet area, there can be only one possible identification.

Mostly. There are a few other birds that have wimpy, trill-like songs. I call these Cheep Trills. Palm warblers are the best example. It’s a loose rattle that sounds harshly buzzy but weak. Don’t worry about them. They’re primarily confined to boggy areas in Maine — like the Orono Bog Boardwalk — and aren’t likely to be in your backyard except in migration.

To sum up, all the trillers are singing right now. They sound similar to each other, but not identical. Get to know one, then compare it to what you’re hearing in the field. Improve your birding-by-ear skills, starting today.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.

Watch: How to identify the songs of 5 common Maine birds

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