Friday, February 28, 2014

Martens and Wind

Fierce gusts of wind rocked the treetops above me, sending shivers down their trunks. Among the boles of swaying aspens, maples, and firs, I skied with one ear to the sky. Twigs clattered, snow plopped, and cold wood fibers moaned up and down the musical scale. One tree almost buzzed with a high-pitched popping, while another groaned from deep within. I listened carefully to determine the location of the loudest trees, and to gauge their ability to strike me if they came crashing to the ground.

Although the bluster threatened above me, it didn’t quite reach all the way down to the swooping hills and rippled snowpack. I felt protected in the understory of this forest. My eyes were scanning for animal tracks in the days-old snow, but I only saw signs of other skiers. Deep drifts and bitter temperatures have driven many creatures down into the next level of protection: the subnivean layer.

Fluffy snow captures summer warmth still radiating up from the ground. A thin zone opens up under the snow, right at the surface of the ground. Here, the temperature stays at a fairly stable 32 degrees Fahrenheit. Compared to a negative 45 degree wind chill at the surface, that feels pretty balmy!

American martens are one of the many creatures that exploit the subnivean microclimate. These small weasels tunnel through the snow to find food, stay warm, and escape predators. Phil Manlick, a Master’s student at UW Madison, has been studying the “Habitat-mediated foraging and predation risk in reintroduced American Martens.” Recently he gave a dinner lecture on the topic at the Rookery Pub and Fine Dining near Cable, WI. One of his hypotheses is that martens need lots of structural diversity – lots of fallen logs – in their habitat to help them gain access to the subnivean layer.

Once under the snow, martens can forage along the log-lined runways where red-backed voles, mice, shrews, and squirrels also travel. When satiated with a tasty meal, martens have been known to curl up in the den of their prey for a nice warm nap. The snow is an excellent blanket for this lean mammal, who stores little fat and burns lots of fuel to stay warm. Snow also provides cover from other predators. The diets of foxes, fishers, and bobcats overlap with martens’ diets, and those larger carnivores will kill martens to eliminate competition.

American martens were extirpated from Wisconsin in the 1920s, due to unregulated fur harvest and widespread habitat loss. In 1986, wildlife managers developed a marten recovery plan with the goal of reestablishing two self-sustaining populations of martens in the Chequamegon-Nicolet National Forest. But even with cooperation between the Wisconsin DNR, the US Forest Service, and the Great Lakes Indian Fish and Wildlife Commission (GLIFWC), and multiple reintroductions, marten populations in the Chequamegon National Forest are not rebounding as well as wildlife managers and researchers hoped. Phil is trying to figure out why.

Although he’s still mostly in the data collection phase, preliminary results indicate that one issue limiting the American martens’ recovery in the Chequamegon National Forest might be poor juvenile survival. Adults are doing fine, he says, but the young martens, kicked out of their parents’ home range after just a few months, may not be finding enough high quality food to make it to adulthood.

Phil’s research techniques involve gathering hair samples from martens as they explore PVC tubes baited with beaver meat and equipped with a brush. By comparing the ratios of stable isotopes of nitrogen and carbon in the martens’ bodies to the ratios of those isotopes in their various prey species, Phil can get an idea of what martens are eating. Other researchers also identify animal remains found in marten scat to identify specific prey.

The surprising results are that in northern Wisconsin, martens’ diets consist of 40% shrews and 30% deer. In contrast, healthier populations of martens out west and in Minnesota eat many more red-backed voles and squirrels. Why might eating shrews and deer be a problem? Shrews, like the martens themselves, don’t store fat for the winter. With an extraordinarily fast metabolism, shrews must feed voraciously night and day. This makes them the skim milk of the small mammals.

Deer might seem like an improbable food source for a two-pound marten, but evidently, martens are feeding opportunistically on winter-killed and wolf-killed carcasses. The trouble is that deer carcasses are a risky food source. Fishers, wolves, coyotes, and other scavengers are attracted to those same banquets, and make things dangerous for the martens. That competition with other species may be another important factor limiting the martens’ recovery.

Phil suspects that habitat quality has an impact on both food availability and competition. During his summer habitat surveys, Phil found that martens need “nasty forests that you don’t want to trudge through.” By which he means forests with lots of blow downs, snags, large trees (greater than 39 cm diameter), and coarse woody debris. If further data analysis supports that hunch, it might influence how foresters manage the landscape in the future.

Thinking back to those trees groaning and swaying in the tempest above me, it might not be a bad thing if a few of them fell down...after I’ve skied past, of course.

“But these are the woods you love, where the secret name of every death is life again…”  -- Mary Oliver, from Skunk Cabbage

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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, February 21, 2014

Treasure Hunt Part 2

With photos of snowy owls on our memory cards, and sore necks from searching for the great gray owl, we turned onto a side road to a place we knew we’d find treasure.

As the Sax-Zim Bog northwest of Duluth gains fame for its unusual avian residents and visitors, human residents and visitors have added bird feeders here and there to increase viewing opportunities. Two other cars were already stopped across the road from the sunflower seed feeders nestled in a tiny clearing in the roadside swamp. Peanut butter residue covered many of the perches.

The treasure we sought at this station was much smaller than before. Weighing in at less than half an ounce, boreal chickadees seem an unlikely candidate for Arctic living. Although their normal range is farther north in Canada and Alaska, a pair seems to have taken up residence here. Word on the street is that they love peanut butter.

As we waited for the boreal chickadees to appear, a gregarious flock of our regular black-capped chickadees entertained us. After a bit, a troupe of soft-feathered gray jays (also known as Canada jays, whiskey jacks, and camp robbers) swooped in with no fear. Gray jays have some unique winter adaptations – like feathered nostrils – that allow them to spend their lives in the far north, even breeding during late winter when temperatures could fall to -20 degrees.

Gray jays need many calories to keep them going, and they store food to supplement their diet during lean times. These resourceful critters use sticky saliva to glue small food items to tree branches above the height of the snow line. Cold temperatures in their preferred habitats prevent cached food, even chunks of meat, from spoiling. Some boreal tree species may even contribute antibacterial compounds that help the food stored under their flaky bark stay fresh.

After observing the feeders for over 40 minutes, we wished we had more winter adaptations, and more food. Luckily, as we watched, a volunteer showed up with a huge bag of birdseed, and filled all the feeders. We thanked him profusely as the action picked up. In no time, we spotted the rusty sides and brown cap of the boreal chickadee as it came to visit the feeders.

After our three successful sightings of target birds, it was time to move on. We peered intently into the forest, still trying to catch a glimpse of the elusive great gray owl. The Phantom of the North had been spotted near the feeders in recent days.

“Stop! What’s that?” came the cry from the back of the van. We extricated ourselves from the van to get a closer look. As the first pair of binoculars focused in, the shape unwound itself from the tamarack branch and went scurrying down the trunk. Red squirrel. Back in the van, the rest of the great gray owl’s reported habitat streamed past our windows with no luck.

Soon we found ourselves on another long, straight stretch of road, thick with black spruce trees on either side. This time our treasure showed itself readily. The dark silhouette of a northern hawk owl stood out cleanly against the blue sky.

Although northern hawk owls tend to avoid dense spruce-fir forests in favor of more open hunting grounds, the road ditch here must provide enough space for hunting. Even swaying slightly in the rising wind, this owl could detect prey scurrying half a mile away--by sight.  Like the snowy and the great gray, this little guy can also hear and hunt small mammals under the snow.

As we watched, the dark brown owl swooped several yards to a new perch. Its short, pointed wings, compact body, and long, tapered tail certainly gave the impression of a hawk, as did its daytime hunting. But it is a hawk in name only.

Enthused by the discovery of yet another treasure, we resumed our search. This time our destination was bird feeders outside a small wooden building accessorized by two purple porta potties. The brand-new, just-insulated welcome center is a project of Friends of the Sax-Zim Bog. Pine grosbeaks chattered at the feeders as we chatted with the full-time naturalist. She assured us that no one else had seen the great gray owl that day either.

Afternoon sunshine slanted across the road, and directly into our eyes, as we took one more drive past the great gray owl’s reported hunting grounds. Still, the Phantom of the North eluded us. We felt rich anyway, happy with nice views of two northern owls, several unique songbirds, and a beautiful winter day in the 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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, February 14, 2014

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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, February 7, 2014

Barred Owls

The noiseless glide of soft, gray wings caught my eye. Then, stillness. No matter how hard I squinted, I couldn’t resolve the dark shape into a branch and the owl I knew had just landed there. Fading light under gray skies, combined with the owl’s pattern of light and dark bars on its chest, created perfect camouflage.

Nevertheless, I felt grateful to catch even a glimpse of such a graceful nocturnal creature. On a sunnier day, it might stay hidden against a shady tree trunk until dark, avoiding detection by its nemeses – crows or great horned owls. The gray afternoon and impending breeding season must have lured it from its usual daytime roost.

Most of my encounters with barred owls have been vocal. Their distinctive eight-note call is often phrased as "Who cooks for you? Who cooks for you-all?" and has earned them the nicknames “Eight Hooter” and “Le Chat-huant du Nord,” which is French for "The Hooting Cat of the North.” On many childhood nights, conversations between my dad and the barred owls echoed over the Iowa hills. There were also my first attempts at calling in the owls, which often got a response from the local coyote family instead.

As a Girl Scout Camp counselor, I remember a very long week in a unit of ten-year-olds when the barred owls out back decided to practice their full repertoire of calls. When the awful jumble of hoots, screeches, cackles, and yelps broke into a frenzied and raucous monkey-like squall, we ended up with a bevy of scared girls in the counselor tent—and very little sleep. I have to admit that the barred owl’s voice can still send shivers up my spine. Now, as breeding season ramps up, is a good time to listen for their haunting calls.

While their voices can be eerie, the silence of owls is even more intriguing – and lethal. Not only does silent flight enable owls to sneak up on prey, it also allows them to hear a mouse – under a foot of snow – pinpoint its location, and punch sharp talons through the icy crust with deadly accuracy. Any flight noise would obscure the soft scurries of those subnivean snacks.

One secret to silent flight is broad wings with large surface areas that reduce the need to flap. Owls just seem to float through the air. In addition, anyone looking at an owl wing can see a comb of stiff feathers along the leading edge, and a flexible fringe on the trailing edge of the wing. Those fringes break down air turbulence into smaller currents called micro-turbulences, which generate less sound. (If you’ve never studied an owl wing, then check our summer program calendar for owl prowls and raptor programs at the Museum!)

Looking closely, you may also notice a soft, downy covering on the top of the wing. A photographic study of owl feathers revealed a surprising 'forest-like' geometry of the down material, and scientists at Lehigh University's Department of Mechanical Engineering and Mechanics think that this may be another key to eliminating sound.

Dr Justin Jaworski, a scientist on the project, predicts that “If the noise-reduction mechanism of the owl down can be established, there may be far-reaching implications to the design of novel, sound-absorbing liners, the use of flexible roughness to affect trailing-edge noise and vibrations for aircraft and wind turbines, and the mitigation of underwater noise from naval vessels.”

Just being quiet isn’t enough. Owls have especially acute hearing; due in part to their satellite dish-like facial disks that funnel sound, and to a right ear that is higher on their head than the left ear. The sounds of a scampering mouse—like the ones who have left numerous hopping tracks quilted into the snow near my skis—will reach one ear more quickly than the other ear. By using this triangulation, owls can pinpoint the location of their prey—even below snow—even in complete darkness.

Once prey is located, owls’ other weapons kick in. Their sharp talons and hooked beaks are equally strong, unlike other raptors who have stronger feet and weaker beaks. Owls use both to grab, kill, and eat their prey.

The owl was still nearby, I knew, since I hadn’t seen it leave the branch. Although I couldn’t see it in the fading light, I knew its huge eyes could be watching me. Owls have excellent binocular vision, which allows them to judge distance and depth. Owl eyes are more than twice as large as the average size for birds of the same weight. In fact, their eyes are elongated tubes held in place—unmoving—by bony structures called sclerotic rings.

To compensate for not being able to move their eyes, owls can turn their heads up to 270 degrees (NOT 360) left or right from the forward facing position, and almost upside down. Owls’ fourteen neck vertebrae (twice as many as we humans), single pivot point within the cervical vertebrae, special muscle structures, and a special arrangement of the jugular veins all contribute to their flexibility.

Without downy feathers to insulate me, the chilly evening crept into my core. Pushing my skis forward, I tried to catch one more glimpse of the camouflaged critter. This tested the flexibility of my neck (only about 180 degrees), strained my human eyes, and made far more sound than those soft, gray wings.

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 to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,