The ghostly white bird that yonder comes

A fluffy visitor from the north has captured the state’s imagination.

THE SNOWY OWLS are back in force in Wisconsin this winter.

The majestic Arctic hunters fly hundreds of miles south en masse every four to five years in poorly understood events that scientists call “irruptions,” and the current one is shaping up to be among the largest ever documented in Wisconsin. Ryan Brady, bird monitoring coordinator for the state Department of Natural Resources, believes roughly 200 different snowy owls have been spotted across the state, including at least a handful in Milwaukee County.

The biggest of North American owl species at 3-6 pounds, snowy owls have large yellow eyes that contrast strikingly with their white plumage. Their good looks – and their preference to hunt and be active during the day, when they can be seen – cause quite a stir among birdwatchers and non-birders alike. (It doesn’t hurt that Hedwig from the Harry Potter series was a snowy, too.) “In all my time working with birds, no species has resonated more with the non-birding public,” Brady says, “even more than eagles, cranes and the other white birds.” To satisfy that curiosity, groups like the Wisconsin Society for Ornithology and Sheboygan County Audubon Society are holding field trips so members and non-birders alike can take a respectful look.

But there’s also interest in snowys for weightier reasons: Better understanding their irruptions is important because they breed in polar regions where climate change’s effects are most dramatic.

There’s disagreement as to the causes of irruptions, but many experts believe they’re a response to booms in the population of lemmings, the hamster-like rodents that are snowy owls’ primary food source in the Arctic. Owl populations rise as well, and the younger birds spread out by heading south. And it’s also now clear that the global snowy owl population is much smaller than scientists once believed – recent studies suggest it may be as low as 30,000, barely a 10th of past estimates.

One collaborative effort at understanding the birds and their movements is Project SNOWstorm, which tags healthy snowys with cellular transmitters on little backpacks to track their movements in precise detail, for years at a time. More than 50 owls have been tagged in 11 states from North Dakota to Maine since 2013, including six in Wisconsin. This year, the project aims to tag five more snowys here with the $3,000, ounce-and-a-half transmitters funded by bird organizations and foundations in Wisconsin.