Fear of Predators Takes Surprising Toll on Animals

If an animal species lives in an area where it's surrounded by predators, you wouldn't expect to see robust population growth. But what if the animals just think they're surrounded by predators? Turns out, the same applies, according to a new study out of Canada's Western University. The researchers say that fear alone can diminish animal populations—and the direct effects of that fear can ripple through multiple generations. In this case, the study involved sparrows. The research team rigged speakers by the birds' nests and pumped in sounds of danger (hawks, crows, etc.) to some and sounds of non-predators (frogs, ducks) to others. This continued over three annual breeding seasons, per a university release. The results were striking.

Birds subjected to the sounds of danger raised 53% fewer chicks to a reproductive age than the other sparrows, reports New Scientist. Not only did they lay and hatch fewer eggs to begin with, but the chicks that were born appeared to pay a price with slower development. Researchers speculate the adult birds were so worried about protecting their nests they couldn't forage for food as much as usual. As a post at Hakai Magazine puts it, the "young sparrows that successfully grew up in this atmosphere of fear remained at a disadvantage into adulthood." That is, they sang fewer songs, had fewer offspring, and didn't live as long as birds raised in the non-fear atmosphere.

"By changing the way one generation of sparrows performed as parents, fear appeared to have a cumulative effect that spanned generations," reads the Hakai summary. The scientists projected that a particular sparrow population could be cut in half in just four years under these circumstances. "These results have critically important implications for conservation, wildlife management, and public policy," says one of the researchers, ecologist Liana Zanette, per the release. "The total ecosystem benefits gained from conserving or rewilding native predators, and the full devastation wrought by introduced predators, must all now be reevaluated." A fear researcher at UCLA not involved with the study calls it "really extraordinary," per Hakai. (More discoveries stories.)