01 Greater Yellowstone Bioacoustics

The Greater Yellowstone Ecosystem,
heard all year.

Passive acoustic monitoring is simple: leave a recorder in the field and let the animals announce themselves. A grid of recorders listens everywhere at once, day and night, for months, and a species only has to call once to be counted — without disturbing the animals. Knowing who is there, and where, is what makes it possible to protect the habitat they depend on. Yellowstone scientists inside Yellowstone National Park and citizen scientists across the Greater Yellowstone Ecosystem run grids of autonomous recording units. They record around the clock, through every season, in places no survey crew can stand for long. That archive is where the region’s rarest voices turn up — if you know what to listen for. Each tab below is a field guide to one group: what the call looks like on a spectrogram, when and where to search first, and what to rule out before calling it.

A discovery and verification aid, not an occupancy model. Pick a species to see its Yellowstone status, the published shape of its territorial call, when and where to search the archive first, and which sounds to rule out before confirming. AI finds candidates; a person confirms the sound. Occurrence status follows Yellowstone National Park’s own bird-record categories — confirmed breeder, uncommon or rare, accidental or vagrant — and the owl-survey standards in the park’s annual bird reports, cited below.

Flammulated Owl

Psiloscops flammeolus

Accidental, vagrant or few observationsManual verification required
Photo: USGS (Patuxent Wildlife Research Center) · Public domain (US Government work) · Wikimedia Commons

The flammulated owl (Psiloscops flammeolus) is a small migratory North American owl in the family Strigidae. It is the only species placed in the genus Psiloscops. The flammulated owl is a small, nocturnal owl approximately 15 cm (6 in) long with a 36 cm (14 in) wingspan. It breeds from southern British Columbia and the western United States to central Mexico. It is a neotropical migrant and winters south of the United States, but also in South Texas, Arizona, and California. The flammulated owl nests in tree cavities and has two to four young at a time after a 26-day incubation period. The young are able to forage for their own prey after about 25–32 days. Wikipedia, CC BY-SA 4.0

Territorial call
Repeated low, soft, ventriloquial single hoot (sometimes a two-note hoo-HOOT); voiced, not whistled. Repetition rate and the low, hollow quality matter more than loudness.
FrequencyFrequency bands are practical spectrogram screening ranges, not hard species boundaries. Distance, habitat filtering, recorder response, sex and call type can shift apparent frequency content. Confirmation should combine frequency, cadence, phrase shape, season and habitat.
~400–500 Hz fundamental (measured); screen 300–700 Hz. Second harmonic 12–20 dB weaker.
Duration / cadence
Single hoots are brief (~0.2–0.3 s); a bout persists for minutes at a near-metronomic rate
Inter-call gap / repetition
~2–3 s between territorial hoots (GTR-260); measured medians 2.3–2.5 s across the eight clean open recordings.
When to search
Late May–Jul · Full darkness; emphasize first several hours after sunset
Habitat prior
Older, relatively dry, open Douglas-fir/ponderosa-type forest with large trees, cavities/snags and small grassy openings.
PNW-Cnet context
PNW-Cnet v4 class PSFL · published precision 0.849 / recall 0.850 at ≥0.95 threshold

What to listen for

A long train of soft, low, voiced hoots at remarkably steady 2–3 s spacing, sitting at about 400–500 Hz — lower than any other small owl here and in the Long-eared band. The notes sound hollow rather than whistle-like.

Spectrogram pattern

A short blob at ~400–500 Hz with a weak second harmonic near ~900 Hz, repeated every 2–3 s. The band alone will not separate it from Long-eared; the steady 2–3 s cadence, the short note and the season (late May–July) will.

Likely acoustic confusions — check these before confirming

  • Long-eared Owl. The critical manual check: the same band. Both are repeated low hoots at ~300–500 Hz. Flammulated's hoot is shorter and softer at a steady 2–3 s; Long-eared's is deeper and more forceful, 2–4 s apart, and can run past 200 hoots. Season helps: Long-eared calls late winter–spring, Flammulated late May–July.
  • Northern Pygmy-Owl. Repetitive clear toots near ~1 kHz — more than double Flammulated's pitch — clearer and more whistle-like, often in daylight or at dusk.
  • Northern Saw-whet Owl. Saw-whet's song sits near ~1.1–1.3 kHz, far above Flammulated, and runs at ~2 notes per second; Flammulated is one hoot every 2–3 s.
  • Western Screech-Owl. Sits higher (~600–720 Hz) and its territorial song has the accelerating bouncing-ball cadence rather than isolated, evenly spaced hoots.
  • Distant Great Horned / other low owl calls. Attenuation and harmonics can make distant low hoots appear deceptively small on a spectrogram; compare fundamental and phrase cadence.

Where the numbers come from. Frequency measured from eight open iNaturalist research-grade recordings (Oregon, Washington, British Columbia): per-recording median fundamentals 422–500 Hz, second harmonic 12–20 dB weaker, hoots 2.3–2.5 s apart. Cadence: GTR-260, McCallum 1994. Hz was not published by any cited source. The grid's own recordings are not used as a source until they are verified.

Sources for this species: Cornell · GTR-260 · McCallum 1994 (RM-GTR-253) · PNW-Cnet v4 · Yellowstone checklist 2021 · Yellowstone bird report 1999

Hear it · Flammulated Owl

Example recordings from the grid. Pick one to play it.

More recordings: iNaturalist · Macaulay Library · xeno-canto

Loading the player…
Flammulated Owl · Photo: USGS (Patuxent Wildlife Research Center) · Public domain (US Government work) · Wikimedia Commons
02 Sources

Where the guide comes from.

Occurrence status is from National Park Service records. Vocal characteristics are published descriptions. Screening bands and search priorities are practical heuristics built from them — not species boundaries, not occurrence probabilities.

Yellowstone National Park occurrence and breeding status

What the park’s records say · Flammulated Owl

  • 2019 report — Not detected in any of the seven survey years (2013–2019) of the Northern Range owl surveys.
  • 2016 report — Listed under Accidentals and Vagrants (Appendix B).
  • 1999 report — A small owl killed by Black-billed Magpies in front of the administration building on 30 October 1999 was identified as a Flammulated Owl and preserved as a specimen — the park's documented record.

Great Gray Owl

Flammulated Owl

Boreal Owl

Northern Saw-whet Owl

Northern Pygmy-Owl

Long-eared Owl

Short-eared Owl

Western Screech-Owl

Burrowing Owl

Snowy Owl

Great Horned Owl

PNW-Cnet

The detections on this page were found with GrizCam Desktop — its GrizEars workspace runs classifiers such as PNW-Cnet across a recording archive, and its 3D spectrogram is the player above. Free for any recorder’s audio.

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