Laura Erickson's For the Birds

Owl Diets

I’ve been collecting accounts of any observations people have made of northern owls feeding on prey larger than mice. As enormous as they are, Great Gray Owls are mouse and vole specialists, and although many species accounts indicate that they sometimes eat squirrels and rabbits, there isn’t much known about their eating habits of these larger prey items. Dr. James Duncan, an owl authority from Winnigpeg, emailed me that squirrels, grouse, weasels, star-nosed moles and recently even a northern hawk owl, occasionally are taken, but that little is known about them taking or eating these rarer prey items.

Virtually immediately after I made this request on my radio program and in the Duluth News-Tribune, I started getting phone calls and emails from people who had observed Great Gray Owls killing and eating squirrels and rabbits this year. In Duluth, a population of feral domesticated rabbits (some interbreeding with cottontails) has become established on Minnesota Point, and residents there seem mostly happy that the owls may be providing a solution to their rabbit population explosion. But one Duluthian in a different neighborhood had become rather attached to two rabbits that visited her yard, and was understandably less pleased when a Great Gray Owl dispatched one of them.

The largest prey that I’ve so far heard of a Great Gray Owl killing was via a second-hand report from a falconer. His Red-tailed Hawk came down upon a Great Gray Owl, and when he called off his bird, he found that the owl was feasting on a snowshoe hare. Considering that healthy snowshoe hares outweigh healthy Great Gray Owls, bringing down one was no mean feat.

Great Gray Owl stomachs examined by David Willard of the Field Museum of Natural History during the last invasion in 1995-96 showed only mice and shrews. But based both on accounts of people and of a photograph sent to me by one observer, the owls are ripping meat off these large prey animals and may not be swallowing many bones, making the presence of large prey animals hard or impossible to determine from stomach contents. This means it may be more common for Great Gray Owls to take large prey than we realize. Great Gray Owls don’t have powerful talons, but their claws are long and sharp, and their beak sharp and powerful, so if they drop down on a rabbit and bite it quickly, they may win the battle. Great Grays don’t have enough body mass to lug off large prey items, which explains why so many people who have observed this are seeing the owls remain down with their prey, eating chunk by chunk over long hours or even full days. The owls have been observed sitting on their prey for many hours, often over a two-day period, feeding occasionally. Sitting on this large prey seems to serve two functions—it both protects it from being stolen by other predators and keeps it reasonably thawed.

This year’s invasion is affording us a unique opportunity to tease out some information about how Great Gray Owls deal with low mouse populations. If any readers see interesting feeding behaviors in these wonderful owls, please email me at chickaeee@lauraerickson.com with your observations.