Barred owls and megafire hit native owls differently
Flammulated owls declined 71% in severe burns and doubled after barred owl removals; pygmy and great horned owls barely budged.
Source
Divergent responses of native predators to severe wildfire and biological invasion are mediated by life history
Study at a glance
- Design
- Other — Passive acoustic occupancy modeling across megafires and barred owl removal experiment
- N
- N=265 · 265 hexagonal survey cells with 517 ARUs; 80 barred owl/hybrid removals
- Population
- Owls across >6,000 km² of the northern Sierra Nevada
- Outcome
- Site occupancy of flammulated, pygmy, and great horned owls after fire and removals
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Inspect source passages
Barred owls and megafire hit native owls differently
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517 ARUs were deployed across 265 hexagonal cells in 2018 and 2021
We deployed 517 ARUs across 265 hexagonal cells in 2018 and 2021
Barred owl occupancy fell from 0.19 to 0.03 between 2018 and 2020
barred owl site occupancy decreased from 0.19 to 0.03—a reduction factor of 6.3
What they did
Researchers ran passive acoustic surveys (2018, 2021–2023) across >6000 km2 of the northern Sierra Nevada, bracketing the North Complex and Dixie megafires and a lethal barred owl removal experiment (80 birds). Occupancy models tested fire, invasion, and their interaction for flammulated, pygmy, and great horned owls.
What they found
Severe fire cut flammulated occupancy 71% for ≥3 years in near-complete burns, yet occupancy was higher where some high-severity fire occurred (Ψ 0.29 vs 0.16 unburned). After removals, flammulated occupancy at treatment sites rose from 0.09 to 0.18 (about twofold). Pygmy and great horned owls showed little fire or removal response. No fire×removal interaction. Flammulated occupancy was 196% higher in the most rugged terrain; barred owls declined 84% there.
The limits
What it doesn't show
Barred owl densities were already low after removals, so interactions could emerge where invaders are denser. Predation on flammulated owls was not directly observed. Great horned habitat coefficients had wide intervals overlapping zero. Surveys cover a few years postfire, not decades of snag-forest succession.
Key terms
- Barred owl invasion
- Westward expansion of Strix varia, an eastern apex predator competing with and preying on smaller western forest owls.
- Lethal removal experiment
- 80 barred owls/hybrids shot 2018–2022; site occupancy fell from 0.19 to 0.03 (factor of 6.3).
- Flammulated owl
- Small nocturnal insectivore and secondary-cavity nester; most sensitive to both severe fire and barred owls.
- Occupancy (Ψ)
- Probability a site is used, estimated from replicated acoustic detections while accounting for imperfect detection.
- Megafire
- Very large, high-severity wildfire; here the 2020 North Complex and 2021 Dixie Fire.
Flashcards
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In near-complete severe burns, flammulated occupancy fell by about:
Common questions
Did all native owls crash after megafire?
No. Only flammulated owls showed a strong negative response to extensive high-severity burn.
Did removing barred owls help everyone?
Only flammulated occupancy increased; pygmy and great horned owls did not.
Did fire block recovery after removals?
No interactive effect: fire and invasion acted separately at these low invader densities.
Why might pygmy owls be safer from barred owls?
They hunt at dusk and by day, reducing overlap with a nocturnal invader.
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