Snowy owls are doing some unusual things again this year.
The last two winters, people in Michigan saw a lot of them. There were big migrations of owls called irruptions – that’s when they fly south from their breeding grounds in the Arctic.
This year, researchers don’t expect those big numbers again, but they are surprised by how early owls are arriving.
Most snowy owls start arriving here in the middle of November into December, but owls started showing up in the Great Lakes region in mid-October this year.
Scott Weidensaul is one of the founders of Project SNOWstorm – it’s a project that uses GPS transmitters to track the owls as they fly around. You can check out these maps to track the owls' movements.
Why are the owls here so early?
Weidensaul says Dave Evans, a snowy owl researcher in Minnesota, has found that when owls show up early, they’re typically in worse physical condition than normal.
“Usually when we have these really big invasions of snowy owls, like we've had the last couple of years, those are mostly very fat, very healthy young birds, the product of a really productive breeding season in the Arctic,” he says. “But periodically, the prey populations on which these birds depend will crash. There can also be early heavy snows in the Arctic that will seal off the lemmings — you know, the small rodents on which these birds feed — to a significant degree.”
This might be what’s happened this year, Weidensaul says.
So far, a small number of snowy owls have made their way into Michigan, Wisconsin, and Minnesota.
“What often happens with these kinds of limited irruptions of underweight birds, is they come down here thin and then start to bulk up again, because they move into an area where there's more food and they recover their body weight pretty quickly,” he says.
What happened to last winter's tagged birds?
During the big irruption last winter, birders managed to tag four snowy owls in Michigan.
Weidensaul says some of the tagged birds in our region spent the winter in farm fields, feeding on rodents.
"But a number of our tagged birds have moved out onto the Great Lakes,” he says. “And even the birds that spent the winter in interior areas feeding on mammals, once they started migrating in the spring and heading north, they moved out onto Lake Michigan, out onto Lake Superior, Lake Huron, and started moving north on the ice. These birds love ice.”
He says while they're on the ice, snowy owls feed on water birds living in cracks in the ice, like ducks, grebes, and gulls.
But when the owls fly north, beyond the reach of the cell phone network researchers use to record GPS locations, the birds temporarily disappear.
But that doesn’t stop the transmitters from recording data. So when owls fly south again, the team receives “a fire hose” of backlogged data.
“With some of these owls, we can program the transmitters to take a really precise GPS location in three dimensions — latitude, longitude and altitude — as frequently as every thirty seconds,” Weidensaul says. “So it builds this incredibly detailed picture of the moment-to-moment movements of the owl.”
Weidensaul and other researchers are evaluating that data.
“We're just having a field day with it,” he says. “It just gives us insights into the ecology and behavior of these birds that we've never had before at this level of detail."