SNOWY OWLS: What do they eat?

Snowy Owls are back in the Chicago area in a big way, for the second time in three winters. While the speculation about why revolves around a highly successful breeding season in northern Quebec producing an abundance of offspring (for example, see here), whatever the reason, Chicago-area birders are thrilled to have them around. People have even been braving the Arctic-like conditions to get out and see these beautiful, evocative owls (photo by Sebastian Villarreal).

Like during the 2011-2012 irruption, I sent out a call for Snowy Owl pellets to the Illinois birding listserve. Several local birders responded and I was able to procure six pellets, as well as the stomach contents of two owls that were killed in collisions with airplanes at Midway Airport (a not uncommon occurence, unfortunately). This is a summary of what I found. Many thanks to Jerry Goldner, Ethan Gyllenhaal, Josh Feeney, and Carolyn Marsh for helping me get pellets to analyze.

In short: Snowy Owls at Montrose Point, on the Chicago’s north side, like to eat rats. At the southeast corner of the lake they prefer birds. And out at Midway Airport, on the city’s southwest side, voles are on the menu. In other words, they’ll eat whatever’s available! But that’s just from the pellets and stomachs, which only offer a limited snapshot of their diets. To get a better picture, we can use birders’ observations as well. At Montrose they’ve been seen eating coots and rabbits, and one was photographed chasing (unsuccessfully) a Common Goldeneye. On the city’s southside, one was photographed eating what appears to be a fish.

The photo below shows the contents of a single pellet that Carolyn Marsh collected at Calumet Park, a lakefront park on the Illinois/Indiana border. The pellet was mostly feathers, with a few vertebrae mixed in. Recognizing the feathers as coming from a duck, Dave Willard and I headed into the museum's collection to find a match for the more distinctive of the feathers in the pellet. After pulling out study skins of several species, we found a perfect match--Greater Scaup. The bottom photo shows a feather from the pellet against a backdrop of the matching back and wings of a Greater Scaup.