Great Gray Owls: Hunting Adaptations

Environmental & Science Education, STEM, Behavior, Biological Evolution, Wildlife, Nature, Biodiversity, Nature of Science

Ed Hessler

How Great Gray Owls find prey (primarily voles) under the snow is the subject of an essay by Rebecca Heisman, Living Bird magazine, Winter 2024.

Heisman provides a description of the challenges to Gray Gray Owls in finding food. Their prey is "no longer than a ballpoint pen - the ones I most frequently use are almost 14 cm ot 5.5 inches - which they can't see, using only faint burrowing sounds more than a foot (~ 30 cm)  under the snow (up to 18 inches, ~45 cm) to guide them in plunging strikes with surgical precision?

Two scientists who appear unlikely collaborators joined to do some research on this problem. Chris Clark is a biologist at the University of California - Riverside and Jim Duncan is a retires wildlife biologist in Manitoba who founded Discover Owls upon his retirement. Clark's research has been on how some birds maximize and minimize sound when they fly.

Heisman writes that "the goals of their collaboration were simple: to test how snow might absorb and distort the sounds of voles and how that might affect Great Gray Owl hunting strategies." Clark was asked how Great Grays "evolved to fly silently."  And I quote his response at length to provide an example of how predictions are used in science in the design of new investigations.  Here is what he said.

 “'What I call the owl-ear hypothesis and the mouse-ear hypothesis.” The owl-ear hypothesis is that owls fly quietly to avoid interfering with their own ability to detect prey by sound; the mouse-ear hypothesis is that they’re trying to avoid being detected by potential prey.

“'Although these hypotheses aren’t mutually exclusive there are some cases where they make different predictions, and the number-one case is when the environment itself blocks sound."' Heisman continues that this is "when there’s a thick layer of snow on the ground. The owl-ear hypothesis suggests that a snow-hunting owl should have especially well-developed quieting features, so that it can hear its muffled prey over the sound of its own wings. Under the mouse-ear hypothesis, however, quieting features would be less important, because the snow would provide the owl with natural stealth."

Heisman describes the complexity of snow which has important effects on the transmission of sound, describes the investigation which included a model, a proxy, for a vole under the snow, and what it is like to work on projects in the natural world. This research faced cold temperatures which interfered with the amount of data the two scientists were able to collect. They left the field with six successful trials which are suggestive. One of the findings was that their research supports one of the two suggested hypotheses - the owl ear and mouse ear hypotheses.

Heisman includes a quote about the research from a non-participant and I include it because it is about the nature of science. "Katherine Gura, a researcher at the Teton Raptor Center in Wyoming and expert on Great Gray Owl ecology, who was not involved with this acoustics study, was 'thrilled' when she read Clark and Duncan’s paper.

“'This work serves as an excellent example of the fascinating questions we can answer by merging a strong knowledge of the physical properties of snow with wildlife ecology. By testing how sound travels through the snowscape and linking those findings to Great Gray Owl foraging strategies and morphology, this study begins to unravel how this species evolved its unique winter behavior and traits.'”

I thought about the spectre of climate change throughout. I'm sure you will as well. What happens to the owl if...?  I'm sure you did as well. Heisman ends with a question about this adaptation and climate change. I hope in the long run this magnificent creature is not lost.

This not-to-be missed illustrated essay may be read here.