Spring Trill-ogy

These last few weeks, as we’ve taken our dog on his morning neighborhood walk, one thing is clear: the spring trill-ogy is in full song. Rarely have we been out of earshot of the trilling music of Dark-eyed Juncos and Chipping Sparrows—two examples among the vast numbers of birds that produce a song made up of rapidly repeated notes.

If you find it difficult to distinguish among the regularly occurring birds of our area that have these trilled songs, you’re not alone. In addition to the junco and Chipping Sparrow, there’s the Pine Warbler, Palm Warbler, Swamp Sparrow, and for good measure, you can include the Marsh Wren. Add in species like Worm-eating Warbler, which breeds as close as Massachusetts, and Orange-crowned Warbler, which migrates through in small numbers, and you have the making of the type of audio conundrum that can make a beginning birder throw up their hands in despair.

If you’re musically inclined, you may be more intimately acquainted with the workings of a trill. In human terms, it is typically embodied by repeatedly alternating two notes very close in pitch. You can accomplish this on the piano, for example, by rapidly pressing two side-by-side keys, alternating, over and over. Birds, on the other hand, repeat the same sound over and over in rapid succession, perhaps sonically more similar to a drummer bouncing the sticks on a drumhead to make a drum roll.

Lots of birds and other animals make repeated sounds as part of what are sometimes described as motor performance displays. These displays, sometimes in the form of songs, convey information to other members of the species. This information is sent to let others of its kind know that it is a strong individual, and that any impulse to challenge is best left alone. In other cases, the data are transmitted to let potential mates know that the triller would be an ideal partner with whom to raise a brood.

Voice isn’t the only way trills can be sent out. Sure, a number of sparrows and warblers trill with vocal ease, but woodpeckers produce a different kind of trill—commonly called a “drum.” This is created by quickly rapping on a resonant tree cavity (or sometimes a stovepipe, sign, or other structure, as Maine folks upta camp know well). Ruffed Grouse rapidly beat their wings in a special way to make a series of short, low sounds, also typically described as a “drum.”

Many insects make a trilling sound by rapidly vibrating legs or wings, as we know from crickets, grasshoppers, cicadas, and other insects. Some frogs and toads make trills vocally.

Most of us humans may find the trilling songs of birds to be less compelling compared to the melodic songs of birds like robins, mockingbirds, certain other sparrows and warblers like Song Sparrows, and Yellow Warblers. Nonetheless, the trill-ogy of spring begs the question: Why do so many species use them? What exactly is it about a trill that conveys a strong message to potential enemies and mates?

It turns out that repeating the same note over and over, exactly the same way each time, is actually not so simple and easy as you may think. Try it yourself and you’ll see. And doing it faster and for a long time can be physically exhausting. The strongest and most practiced individuals (i.e., longest surviving) can convey those facts about themselves to suitors and rivals by singing trills where the notes are perfectly similar, repeated quickly, and sustained over a long time period.

Even if you can’t tell whether that trill you’re hearing is a Dark-eyed Junco or a Chipping Sparrow, we challenge you to start listening to it a little more closely. Does the trilling rate remain constant or begin to slow down or get a little sloppy at the end? Are some trills slower or faster, and does the rate change over the day or when there’s more than one individual nearby? If you start to notice some variation and differences, you may be getting a peek into what the birds are paying attention to every day.

—Allison & Jeff Wells