What If Gone

Species → Barn Owl

Barn Owl

Tyto alba

7,000,000 mature individuals worldwide, median of a wide estimated range
Extinction risk Least Concern
AgriculturalBiological controlPredator
Barn Owl (Tyto alba)
Photo: Luc Viatour, Wikimedia Commons (CC BY-SA 3.0)

What if it disappeared?

Impact Moderate
1 year

Without barn owls, the roughly 616 rodents a pair removed on average per breeding season (up to 899 in the most productive boxes of a camera-monitored Napa Valley study) simply stop being taken out of the vineyard — a removal that ends the very first season without them.

Documented
Detail

Johnson, M.D. & St. George, D. (2020). Estimating the number of rodents removed by barn owls nesting in boxes on wine-grape vineyards. Proceedings of the Vertebrate Pest Conference, 11(29), 18216-18228.

Cameras installed in Napa Valley vineyard nest boxes directly identified prey brought to the chicks, rather than inferring consumption from regurgitated pellets — a method that precisely quantifies the scale of removal that stops cold the moment a pair of owls disappears.

10 years

After several years without owls, vineyards would likely see their rodent populations converge toward the level already measured in vineyards where owl activity is currently lowest — 38 to 52% more rodents than in a high-owl-activity vineyard — with far less vigilant animals, lacking that same fear effect.

Extrapolated
Detail

Extrapolation à partir de Larson, Baldwin & Johnson (2026), qui comparent des vignobles à forte et à faible activité de chouette effraie au même moment : le raisonnement transpose cette comparaison spatiale en projection temporelle d'une absence prolongée, jamais mesurée comme telle.

The reference study combines giving-up-density food trays — a classic measure of perceived predation risk in rodents — with monitoring of owl activity at nest boxes, across six separate vineyards observed at the same time. Nothing directly measures how a single vineyard changes year over year after its nesting owls disappear completely.

What's missing to confirm it: No study has directly measured how a single vineyard changes over several years after its nesting owls disappear completely — only a comparison between vineyards with different activity levels, at the same point in time, is available.

100 years

Over a century, the commercial pitch for owl boxes — cutting back on anticoagulant rodenticides — would likely run in reverse: without that biological control, vineyards would probably lean more heavily on those chemicals, whose secondary poisoning of foxes, coyotes, and other raptors is already documented elsewhere.

Extrapolated
Detail

Extrapolation à partir des cas documentés d'empoisonnement secondaire aux rodenticides anticoagulants chez le renard, le coyote et d'autres rapaces, combinés à l'absence de contrôle biologique par la chouette : aucune étude ne mesure directement le volume de rodenticides qu'une région viticole entière utiliserait après un siècle sans chouette effraie.

Available studies measure the owl's effect on the rodents themselves, not the change in growers' practices during a prolonged absence — a grower without owls has little equivalent biological-control option and would likely turn to rodenticides, whose secondary toxicity to wild predators is, on its own, well established.

What's missing to confirm it: A tracking of rodenticide volumes purchased or applied across an entire wine-growing region, over several decades of complete barn owl absence, remains to be conducted.

1000 years

Over a thousand years, other rodent predators already present — snakes, foxes, small daytime raptors — would likely take up part of the gap left by barn owls, without ever matching their nighttime efficiency or their documented fear effect on rodents. Vineyards would likely remain more dependent on rodenticides than they would have been with owls, on a lasting basis.

Hypothesis

Documentation

Last verified: August 16, 2026