Barn owls swoop down on rodents and swallow them whole – gophers, voles and mice, gone in a few gulps. But how do they keep down all that food? Well, they don’t. In a few stomachturning steps, they transform the varmints into compact balls of fur and bones known as pellets.

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The secret to turning a whole rodent into an owl pellet is in a barn owl’s stomach. It has two chambers.

The first chamber oozes digestive juices, like our stomach. The second one – the gizzard – squeezes the rodent remains with powerful muscles. The fats and proteins get absorbed. After about eight hours in the gizzard, the fur and bones become tightly compacted into an oval that the owl regurgitates.

+ What can scientists learn by studying what's inside owl pellets?

“I think it’s really fascinating you can study their diet so easily by dissecting these pellets,” said Matt Johnson, who oversees the Barn Owl Research Team at Cal Poly Humboldt, in Arcata, California. He and his students monitor 300 nest boxes set up by winegrowers in the state’s Napa Valley.

Winegrowers invite barn owls (Tyto furcata) to raise their young in nest boxes. By hunting gophers and voles, which can damage grapevines, barn owls help with pest control.

Dissecting owl pellets and pulling out the bones hidden inside helps researchers identify what animals a barn owl ate and how many.

In Napa, “voles, mice and gophers make up 90% of what they eat,” said Johnson. “Mice are almost always the third place in that list.”

“Their diet varies from place to place and year to year,” he added. “We’ve collected some pellets that are majority voles, or majority gophers.”

+ How many rodents can a barn owl kill?

While a graduate student at Cal Poly Humboldt, Dane St. George estimated in 2020 that a family of barn owls living in and around a vineyard in Napa can eat 3,500 rodents a year. By tracking the barn owls’ movements, he found that almost 45% of the rodents they killed came from within vineyards.

+ Find additional resources and a transcript on KQED Science:

https://www.kqed.org/science/1979934/...

+ The young barn owl coughing up a gigantic pellet in our episode was filmed by a camera in a nest box in Israel. Watch the whole video here:    • Amazing, Barn Owl Nestling Regurgitat...  

And livestream barn owls, kestrels and other birds here:    / chartergroupbirdcams  

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