Human Noise Robs Owls of Their Ability to Hunt

Sounds from natural-gas extraction sites can reduce birds’ ability to find and capture prey.

The Northern Saw-Whet Owl is the Daredevil of birds.

Though it’s not blind like the red-suited Marvel Comics superhero, it can—and does—hunt prey using just its powerful ears. Even in total darkness, the Northern Saw-Whet owl can lock on to the sounds of a mouse moving nearby, then swoop down and capture its meal in its sharp talons.

And as with Daredevil, that auditory super-skill can be disrupted. New research published in the journal Biological Conservation finds that for every decibel of added noise, saw-whet owls’ hunting ability declined dramatically. Their odds of detecting prey fell 8 percent per decibel, while the odds of actually striking the prey they did detect fell 5 percent per decibel. By the time noise reached 61 decibels—a little louder than a busy restaurant—the owls completely failed to even notice nearby prey.

Lead researcher Tate Mason, currently education coordinator for the Peregrine Fund’s World Center for Birds of Prey, says the research was inspired by early studies into bats, which found that the flying mammals had to increase their hunting search times when flying near noisy highways. “We wondered if other acoustically specialized predators, in particular birds, could be facing the same scenarios,” Mason says.

Mason and his fellow researchers set out to examine the problem. Instead of highways, though, they designed their experiment to replicate the sounds produced by natural-gas compression stations.

“Compressor stations are relatively novel on the landscape,” Mason says. “They are increasing, and they run 24 hours a day, year-round.” That makes them potentially more impactful than highways or airports, which create a lot of noise during the day but can be much quieter at night when owls tend to hunt.

The team captured two groups of owls and placed them in a large blackout tent where they could replicate the compressor noise levels, frequencies, and other conditions. They also released lab-born mice into the tent. When there was no noise, the owls instantly started tracking the mice and often flew down to capture them. That response lessened as the noise levels increased. When the sound levels replicated conditions that would be found about 50 meters from a compression station, “the owl would not even notice the mouse,” Mason says.

Although he suspected that the birds would have impaired hunting ability, the complete failure surprised him. “The impact was more profound than I thought it would be,” he says.

(The clips below, courtesy of Mason, show the difference between a Northern Saw-Whet Owl hunting a mouse in a natural environment versus one hunting in a compressor-sound-filled environment.)

The new research adds to knowledge of how human-generated noise affects birds, says Sarah Thompson, a wildlife biologist with the U.S. Geological Survey, who has studied the impact of oil and natural gas extraction on grassland birds. Her team’s research, published last year, found that some species, such as the Sprague’s Pipit, stayed as much as 350 meters away from fracking well pads. She says papers such as Mason’s are interesting because they start to reveal why some species may be avoiding these sites.

Bangor University lecturer Graeme Shannon led work on a paper published last year that synthesized prior research into the effects of noise on all manner of wildlife. He calls the new study “fascinating.” “These are noise levels that can readily extend hundreds of meters from an active drill rig or a busy highway,” he says, “which in effect drastically reduces the suitable habitat for an acoustically specialized predator such as the Northern Saw-Whet Owl.”

Mason says that’s an important aspect of his research. “The quiet places on Earth are becoming few and far between,” he says. Protecting those naturally quiet spaces from intrusive noise, he says, will help acoustic specialists such as saw-whet, Great Gray, and Northern Spotted owls. “We have the ability to know ahead of time that there’s a threat out there that could be compromising owl habitat. If you deal with that before we see population declines, we can get ahead of the game as far as conserving our wild creatures.”