In 2014, a paper appeared in The Proceedings of the National Academy of Sciences arguing that the hermit thrush, Catharus guttatus, sings in pitch intervals that conform to the harmonic series.
The paper, by the composer Emily Doolittle and the biologist Henrik Brumm, analyzed 71 recordings of fourteen different males. The conclusion was modest but specific. The intervals chosen by the bird were closer to whole-number frequency ratios than would be expected by chance.
This is not, the authors were careful to say, the same as the bird singing in a Western musical key. It is something more interesting and more limited. The bird, like the human composer, prefers certain intervals over others, and the preference is not arbitrary.
Marius Doyle read the paper in 2014 and again in 2026, and went looking for a hermit thrush.
The bird is a North American species that breeds in coniferous and mixed forest from Alaska south through the Rockies and across the boreal east. In the eastern range it nests in Vermont, New Hampshire, and northern New York. By late May it is on territory.
Doyle spent the last week of May at a small camp on Stratton Pond, off the Long Trail in southern Vermont. The cabin belongs to a fellow ecologist named Wren Halpern, who agreed to let it for a week in exchange for the firewood Doyle stacked.
He heard the first hermit thrush at 19:14 on the evening of the twenty-fifth, from a hemlock-dominated stretch about a quarter mile north of the cabin. He heard, in the course of the week, six different individuals, and recorded four.
The song is built on a clear template. There is an introductory note, held for roughly half a second. Then a phrase of three to seven shorter notes, usually descending. Then silence of three to ten seconds. Then the cycle begins again, at a different pitch.
The thing the bird does, that no other North American thrush does as cleanly, is shift the pitch of the entire phrase from one rendition to the next. A male will sing the same melodic shape three times in a minute on three different fundamental pitches.
The shifts are not random and they are not chromatic. The pitches the bird chooses tend to cluster, across the recordings analyzed by Doolittle and Brumm, around the intervals of the natural overtone series.
In musical terms this means the bird favours octaves, perfect fifths, perfect fourths, and major thirds. It avoids the sharp second and the diminished fifth. It chooses, in effect, the intervals that have made up the bone structure of human music for at least two thousand years.
Doyle's own ear in Vermont was less analytic and more affected. He sat on a flat rock above the pond at dusk on the twenty-eighth and listened to a single male sing for forty-one minutes.
The bird used six distinct pitch levels in those minutes. Doyle had a smartphone tuner with him, the same one he uses for his daughter's cello practice. He logged the introductory note of each phrase.
The pitches, transcribed, came out roughly to: E above middle C, the G above that, the B above that, then the same E, then a C-sharp slightly flat, then the G again. The intervals are familiar to any musician. They are the notes of an E major chord with a leading tone added.
Doyle does not want to overstate this. One bird on one evening tells you very little. But it agrees with the published recordings, and with what every patient listener since at least Henry Beston has said about the species.
What is striking is the silence. The hermit thrush sings, then waits. The waits are long, sometimes ten seconds, sometimes more. The waits are part of the song.
A Catharus thrush sings into the silence and lets the silence do its work. A wood thrush, by contrast, runs phrases close together. The hermit's silence is the formal equivalent of the rest in classical music.
What the Doolittle paper, and the long history of musicians' attention to this species, suggests is something modest and worth holding onto. The intervals that please human ears appear to be intervals that the hermit thrush also finds productive.
Whether this is because both species are responding to the same physical constraints on what makes a clear, distinguishable signal in a forest, or whether it is something stranger, is not settled.
Doyle leaves Stratton Pond on the third of June. He will be back in early July to band the thrush nestlings if he can find any. The recordings will be deposited with the Macaulay Library, like Wynn's, and added to the small archive of careful field documents on a species that has been written about, badly, for two hundred years.
