Do Red-breasted Nuthatch Migrate Triennially?

Eric Rasmussen captured this picture of an inquisitive Red-breasted Nuthatch overwintering in the Bitterroot Valley.

As the bird crew dives deep into our archive of fall migration acoustic data, we sometimes find surprises beyond the typical thrush, sparrow, and warbler nocturnal flight calls. As I was proofing fall 2020 data from the MPG Ranch floodplain, the quiet, beguiling, and familiar "yank" of a Red-breasted Nuthatch broke the otherwise steady stream of Swainson's Thrush flight calls. I paused and saw a spectrogram that looked vaguely like a layer cake, not a hockey stick. I checked the time and saw "0:35 am", well outside of the timeframe, we would expect activity from a resident, diurnal bird.


We use the custom, open-source software Vesper to manage our acoustic data. The "thrush" detector we use isolates sound clips of duration and frequency similar to the nocturnal flight call of a Swainson's Thrush (left). The software extracts all calls with similar characteristics, allowing detections like the Red-breasted Nuthatch (right).

Though not a typical migrant like many songbirds, Red-breasted Nuthatch populations exhibit periodic irruptions, where groups move in flocks through the fall and winter. Last October, a social media post by our friends at the Intermountain Bird Observatory near Boise alerted me to watch out for large numbers of nuthatches. And indeed, as I birded this fall and even into the winter, I counted high numbers, particularly in Ponderosa Pine forests. I even saw flocks on the ground, not the usual place to observe this lover of tree trunks and side branches. They joined chickadees, Clark's Nutcrackers, and Red-winged Blackbirds, all extracting seeds from pinecones. But despite seeing so many, it never crossed my mind that we might pick them up on our acoustic monitors.

After my initial acoustic encounter, I noted a handful of nuthatches passing through on 12 of the 14 September nights I looked at, most occurring during the second half of the month.


This screenshot of our Vesper software interface shows the spectrograms and timestamps for Red-breasted Nuthatches during one September night. When we scroll through these spectrograms for proofing, we also hear the associated audio.

These detections match up nicely with the high numbers captured by biologists from the University of Montana Bird Ecology Lab (UMBEL) in 2020, most from mid-to late-September.


Fall banding data from UMBEL on the MPG Ranch floodplain suggests pulses of Red-breasted Nuthatches every three years, including 2020.

We checked with other folks monitoring migration acoustically, and it turns out other sites observed similar patterns, including stations at Cape May, New Jersey, central New York, and Novia Scotia.

We haven't yet processed all of our 2020 data but look forward to seeing if we detected nuthatch migration at other acoustic monitors. In the meantime, when a "yank yank" call stops me in my tracks on a winter bird walk, I wonder if any of my nuthatch neighbors arrived here from distant places after adding surprise to our fall nocturnal soundscape.