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Snowy owl at the outlet of Irondequoit Bay, near Rochester, New York, December 10, 2011. Video: Chris Wood
 
Every four or five years large numbers of snowy owls, those majestic white birds that haunt the Arctic tundra, migrate south and invade the northern United States. It’s happening right now—big time.
 
“Already we can see that this year is one of the biggest irruption years ever for snowy owl,” says Chris Wood, a Cornell University ornithologist and the project leader for Cornell and Լ����Ƶ’s , an online database of avian observations.
 
Through eBird, people around the country are reporting snowy owl sightings. Mapping those data points reveals a flurry of snowies in the Great Lakes region, with smaller numbers of birds being spotted from Washington to Maine, and south as far as Oklahoma and Hawaii.
 

Darker colors indicate higher frequency. on map for larger version.
 
At least a few snowy owls appear south of the Canadian border each winter, says Kenn Kaufman, bird expert and Լ����Ƶ field editor. “For example, there are always some wintering at Boston's , which superficially mimics the appearance of coastal tundra in the Arctic.” But “this is an exceptional season for snowy owls,” he says. Kaufman suspects that there are more individual owls on the Great Plains than around the Great Lakes, but a lower percentage of them are being reported because they’re never seen. “There’s just a lot of good habitat out there that isn’t close to any roads.”
  
The search for food drives the birds—mostly young owls—south. Snowies subsist mainly on rodents, primarily lemmings, throughout the frigid winter months in the far North. Irruptions are typically thought to occur when lemming populations crash. Curiously, that doesn’t appear to be the case this year, Sam Galick, eBird data reviewer:
  

 
Wood emphasizes the importance of entering sightings into eBird. Each one, he says, is like a puzzle piece. “The idea behind eBird is that by bringing these puzzle pieces together, we can get for what that entire puzzle looks like—in this case to try to understand how and why Snowy Owls are moving south,” Wood says. “It will be very interesting to see how the winter unfolds, something that will be made much easier if people —even when they don't see a snowy owl.”
 
To catch a glimpse of the magnificent birds, Wood suggests checking harbors and rocky piers around the Great Lakes, and checking grasslands and reservoir edges on the Great Plains.
  
Kaufman urges anyone who does see a snowy owl to enjoy it from afar. “The birds that come farthest south tend to be the young birds. These inexperienced birds are often hungry and stressed, and we should encourage people to enjoy them from a distance, not to pursue them for closer looks or photos.”
  
So make sure to grab your binoculars before you head out. If you do spot a snowy owl, we’d love for you to share your story in the Comments section below. I’ve only ever seen one, in June 2009 on the tundra just outside of Dead Horse, Alaska. Its bright white feathers were impossible to miss against the green-brown grasses. Even now, it’s still thrilling to think back on it.