Snowy Owl Irruptions

Nature Watch
December 31, 2008

By Susan Benson,
CNHM Director of Education

This winter, snowy owls are being reported across Wisconsin in Ashland, Appleton, Horicon, Oshkosh, and Milwaukee. As early as the beginning of November, snowy owls were even seen in the Chicago area. Birders everywhere believe that an irruption is on its way to the northwoods and Midwest. It is comical to imagine an eruption of owls, but note that the word is irruption, not eruption. An irruption of owls is a rapid and irregular increase in numbers when there is a correlation to a crash in northern rodent populations. Owls move south out of their Arctic and Canadian homes, appearing across the northern tier of states. Scientists believe that they are forced to move southward in search of more abundant prey as the lemming and vole population declines.

One theory is that the lemming population is high during the snowy owl breeding season, followed by a crash in the late summer or early fall as the lemmings run out of food, driving these larger numbers of snowy owls farther south in search of food. Add to this the fact that other snowy owl food such as ducks, have also retreated south. Finally, the snow and ice get so deep it is more difficult for the owls to find anything to eat.

For some areas, such as the Great Plains, the snowy owl movements are regular, occurring every season in about the same numbers. In the Midwest, the movements are more cyclical, with only a few being observed one year and dozens the next. During an irruption year, some of the owls that make it this far south can be in poor shape, and there are many stories of humans saving and rehabilitating snowy owls.

Ornithologists suggest that snowy owl irruptions occur about once every four years, with bigger ones about every decade. Data in Illinois showed 59 owls during the winter of 1980/81 and 46 owls in the winter season of 1991/92.

As a birder or phenologist, keep your eyes open this winter for snowy owls favorite habitats. In the far northern tundra, they live in wind-swept, open plains. They seek out similar territory in this region – grassy, snow-covered meadows, fields, airports, or beaches. Snowy owls like to perch a little higher than ground level, so can be seen on fence posts or brush piles. If you see one, in the spirit of good birding ethics, please err on the side of caution by giving them plenty of room when viewing or photographing them.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at http://www.cablemuseum.org/ to learn more about exhibits and programs.