Treasure Hunt

The van rolled slowly past snowy fields, snowy roofs, and the sparse trees of a northern bog. We were on a treasure hunt. We weren’t searching for your typical treasure, though; our quarry was alive and elusive. “There it is! Pull over!” came the urgent command. Within seconds, we all stood on the gravel shoulder of a rural road, binoculars trained on a snowy owl.

The spindly top of the naked tamarack didn’t look strong enough to hold such a big bird, but the twig bent only slightly under its four-pound burden. True to its name, the snowy owl gleamed white in the chilly morning sunshine. Just minutes before, we’d been scanning the far tree line—convinced that a pile of snow on a branch was the owl we’d been looking for.

Snowy owls aren’t an everyday occurrence in the upper Midwest. Some years they spend all year in the Arctic tundra, defending their breeding territories and hunting small mammals such as lemmings. As far as we know, two things can send owls “irrupting” (an irregular migration of birds into places they don’t normally occur) into the upper Midwest.

The most obvious factor in snowy owl irruptions is too few lemmings. Hungry birds move south in search of food. The second is too many lemmings. This seems illogical, at first, but it makes sense when you realize that if the foxes and weasels can eat lemmings instead of owlets, the owls do better. In a good year, a pair of snowy owls may raise a dozen nestlings who are well fed and protected from predators.

But adult snowy owls defend a breeding and feeding territory year-round.  When there is an abundance of young owls, there is still the same amount of feeding territory as before. These adolescents are pushed south not just in search of food, but of an area to hunt in. The high proportion of first-winter (immature) owls during most invasions provides evidence that high breeding productivity is a major factor in these invasions.

This year most of the snowies irrupted into northern New York, Rhode Island, and even South Carolina, but there are some in northern Wisconsin, Minnesota, and even Iowa. Not by chance, we’ve traveled to one of the best locations for spotting boreal birds at the southern end of their range. The Sax-Zim Bog is a mixture of private and public lands in St. Louis County, MN, less than an hour northwest of Duluth.

Here, the clay soils of an old lake plain hold water within them, and the cold, wet climate has perpetuated a thick layer of peat on top. Bog species such as sedges, tamaracks, and black spruce give it a scraggly look, and open areas likely remind the owls of their tundra home. Most importantly, the bog supports a healthy population of meadow voles and other small mammals.

From the clean, untracked snow, you wouldn’t expect there to be much life here. But of course, the little critters are scurrying happily under the snow in the subnivean layer. Happily, that is, until the owl triangulates the little protein popper’s position, swoops in on silent wings, punches through the snow with strong talons, and breaks its neck with a sharp beak.

Life abounds throughout the drifted fields, frozen swamps, and thickets of trees here, and the snowy owl isn’t the only northern species to call this southern outpost “home.”

Back in the van, we scoured the treetops with our eyes, hoping to catch a glimpse of the Phantom of the North. Great gray owls are circumpolar residents, just like the snowies. The same species we find here, and in Canada and Alaska, is also found in Finland, Estonia, Asia and elsewhere. One pair nests here in the bog. But would we find them here today?

Skip Perkins, our birding guide, advised us to look for great grays perched on the tops of broken tree trunks. “They are about the same color and diameter as their perches, though,” he warned. Like the snowy owl, they listen for the dinner bell from high on their perches. Their huge facial disks help funnel sound and allow them to zero in on subnivean prey.

Great gray owls are the tallest American owls with the largest wingspans, and look bigger than a great horned owl. In fact, they can weigh half as much as a great horned or a snowy owl. They are almost all feathers.

Despite the size of our quarry, the midday sunshine was not helping us locate one. Great gray owls are largely crepuscular, and do most of their hunting at dawn and dusk. Still, hopes were high as we diligently searched the treetops for our next avian treasure.

Whooooo else did we find? Did we see the Great Gray Ghost? Stay tuned next week for more adventures in the Sax-Zim Bog!

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot, http://cablemuseumnaturalconnections.blogspot.com/.