Friday, March 23, 2018

Black Knot in my Bag of Tricks

A good naturalist always has a variety of useful things tucked away in their back pocket or in their bag of tricks. For me, this often this takes the shape of a piece of scrap paper, folded into eighths, with a list of facts or an outline of my hopeful lesson plan for the day (“hopeful” because things never go exactly as planned). Sometimes I literally carry a bag of tricks. It’s a backpack full of preserved grouse feet, a bundle of chimney sweep extension rods for measuring bog depth, magnifying lenses, lengths of yarn, bug jars, and a pocket knife, among other seasonally appropriate items.

Ruffed grouse feet! They grow little "pectinations" along their toes that act as snowshoes in the winter. The foot on the right is a summer foot for comparison. Photo by Emily Stone.

Here's me using the chimney sweep poles to test the depth of the Namekagon Fen. I started with 20 feet worth of poles, purchased 20 more feet, and I STILL don't know how deep the fen is...deeper than 40 feet, I guess! Photo by Jane Weber.

Most of the time, though, my bag of tricks is metaphorical. It’s a filing cabinet in my brain that is stuffed to bursting with a messy array of games, activities, facts, stories, jokes, and demonstrations that I can access through a technique that’s part Google search, part random association, and part luck.

I’ve been adding items to this bag of tricks for a long time. My 12-year stint as both a camper and counselor at Girl Scout Camp provided endless games. The Outdoor Education program at Northland College filled me up with facts and activities. Teaching with creative people in the redwoods expanded my assemblage. Little by little I’ve gathered useful tidbits from every person and place I’ve met. Often people will ask me how I know certain things, or how I know so much about nature. My answer is that it’s been both my job and my hobby to collect facts and fill my bag of tricks to the brim.

We had a crazy bunch of naturalists in the redwoods in spring 2006! I learned so much and had so much fun!

Unfortunately, many things I once tucked safely away in a corner of my brain are now buried in dust, and will never be accessed again without the help of some very specific reminder. Other things are so close to the top that I grab them on pretty much every walk.

Recently, while leading a snowshoe hike on the Friday of Birkie Week, I realized that I hadn’t yet written a column about one of my favorite nature nuggets. It’s right here in my metaphorical back pocket, so let me tell you about it.

Especially in winter, shrubs and trees adorned with knobby, swollen, black growths stick out like a sore thumb. They were first pointed out to me by Craig Prudhomme, my instructor for a field semester at the Audubon Center of the Northwoods. Years of teaching college students had honed his sense of humor toward a combination of nerdy and gross. “It’s arboreal fox scat!” he declared, referring to a recent discussion of gray foxes and their tree-climbing skills. Sometimes I repeat his line, but I rarely have the right audience for it. More often I bring up another common nickname for these thumb-sized black growths: dead man’s fingers (always said in the spookiest voice I can muster.)

While fun, neither of those names is even close to being correct. Gray fox scat doesn’t mold itself around twigs, and dead man’s finger more commonly refers to another black, finger-like fungus that occurs at the base of tree stumps in contact with the soil. “Black knot” is the accepted common name of this odd growth, and its scientific name is Apiosporina morbosa.

Black knot on a cherry twig.

This common fungal pathogen is native across the U.S. and Canada, and only attacks plums and cherries. This fungus can help you identify plants! Chokecherry is a very common component of our local forest understory and edge, and it also happens to be one of the most susceptible species. This combination of factors means that I can find some black knot on almost any nature walk.

The crusty, coal-black galls we notice represent a late stage of the infection. The first symptoms include small, tan, swollen galls on the cherry’s newest twigs. At this time, the fungus is growing inside the tree and causing excessive growth in the tree’s own cells. The fungus overwinters in the galls. The next spring, those galls look like olive green velvet before turning brown and then black. The velvet expels asexually produced spores called conida that fly off on a humid breeze to find a new host. They aren’t very effective at infecting new plants, however. I’ve never noticed the olive green stage, but I think that’s because its two-week-long appearance coincides with the peak of mosquito season in June.

Black knot in the olive green stage, from .

The older, blackened galls are made of both fungal and plant tissues, and will girdle and kill the twig or branch they are on. Even if the fungus doesn’t completely encircle a large branch or trunk, the cracks it causes in the bark allow access to different fungi that will have a go at killing the tree. The black galls also release ascospores that were produced sexually. These can infect wounded tissue, but they can also penetrate directly through the intact surface of an elongating shoot when growth begins in spring.

Black knot isn’t a threat to the health of our forests, but if it happens to infect one of your favorite trees, then aggressive pruning of infected twigs during the winter is your best defense. I’ve noticed, though, that when black knot kills some twigs, the increased sunlight fosters a rainbow of lichen growth. Death is a part of life in nature, just as sure as black knot is part of my bag of tricks.

Lichens grow thick on a cherry tree being killed by black knot. And I couldn't even find my most colorful photo!

Special Note: Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Bee Amazed!” opens on May 1, 2018.

Friday, March 16, 2018

Spring MuseumMobile

Three times a year I get to spend a few days at the elementary school in Drummond, Wisconsin, teaching kids my favorite nature facts using my favorite nature props. Once each season, in Fall, Winter, and Spring, I load seven plastic tubs filled with skulls, furs, graduated cylinders, strips of birch bark, and other oddities into the Museum’s mini-van for a visit to each classroom in grades pre-k through six.

Even though we still have deep drifts of snow and below-zero temperatures at dawn, I recently completed my “spring” lessons. The only times when the topics felt out of step with the weather were in the pre-K and kindergarten circles. Keeping the focus on our five senses, I filled the smell and hearing cups and the touch-bags with new items. Sunflower seeds rattled, a cluster of fake flowers gave its best impression of the smell of lilacs, pine cones prickled and, and a plastic grasshopper got lots of attention. Once I revealed each item, our discussion of seeds growing into sunflowers and lilacs blooming (soon!?) felt like a bit of a stretch.

I transitioned to our next activity by asking how a grasshopper starts its life. Does it begin as a seed? No! It begins as an egg. Reading through the book Chickens Aren’t the Only Ones, gave us plenty of opportunities to discuss what types of animals lay eggs. When the book mentioned dinosaurs, I even passed around a replica of a dinosaur egg fossil.

The page about snakes is my favorite. The text reads that “most snakes lay eggs,” which is true in many parts of the world. In cold climates, though, you often find snakes that are ovoviviparous. In this strategy, the female is internally fertilized, and the young are born alive. In contrast to mammals, the young are nourished by an egg yolk instead of a placental connection. The main benefit, and the thing I focus on with the kindergarteners, is that keeping her babies with her allows the mother snake to move them into warmer places so that they can develop faster. Snake eggs laid in the cold ground risk not developing fast enough to hatch before winter. Garter snakes and northern redbelly snakes are two of our neighbors who use this strategy.

First graders also started their lesson with some talk about eggs, since their lesson focused on frogs. After we acted out the life cycle of a frog (scrunch yourself into an egg, hatch and wiggle with a tail, grow hind legs and then front legs, and finally jump out of the pond and back to your desk), we performed a frog concert. Before the eggs can be laid, the frogs must sing.

We all practiced quacking like wood frogs, peeping like spring peepers, snoring like leopard frogs, and humming like bullfrogs. Then I divided the classroom into four groups and conducted their entrances and exits based on the frogs’ spring phenology. Wood frogs wake up first, and spring peepers follow closely. Just as the leopard frogs begin, the first two go silent. Our bullfrogs carry the late summer tune, and the peepers chime back in when the shortening days of fall confuse them into thinking it just might be spring.

The one MuseumMobile lesson about plants includes second graders transforming their class into a working model of a tree. From the inside out and the bottom up, we imitated all of trees’ most important parts. Our heartwood stood tall and strong, roots made slurping noises as they got water from the ground. “WooooOOOOP!” said the ring of xylem cells as they brought the water up. Now that the leaves had the water they needed, we all chanted “pho-to-synthesis” to help them manufacture sugar. The ring of phloem cells “WOOOoooped” the sugar down to the roots. A line of tough-looking kids with their arms crossed growled “we protect” as they played the role of bark. Finally, the whole tree dissolved into giggles.

Third graders became bears and struggled to collect enough “food” that I had scattered around the room. The average bear needs to eat about 80 pounds of food every 10 days. Not all of the third-grade bears survived, so we talked about the components of habitat and the concept of carrying capacity. During our second round, I held back a third of the food and most of the water to simulate a drought. This caused much distress among the bears, but also drove home the importance of a healthy habitat.

Fourth graders rounded out their year of learning about birds by focusing on nests. I’m always amazed at how well a few photos can capture their attention. We compare the wildly different nests of eagles, goldfinches, loons, and orioles, and then attempt to create our own nests using a core of air-dry clay, and tiny strips of birch bark, pine needles, dried grass, and even flakes of paper from the nest of a bald-faced hornet. It was humbling to compare their ramshackle creations to the precisely constructed nest of a red-eyed vireo.

Red-eyed Vireo Nest. Photo by Vernon R. Martin

In a natural transition from energy conservation, fifth graders switched to water conservation this season. We laughed at the absurdity of my one-liter bottle representing all the water on Earth, but as I poured out 30 milliliters to represent the tiny fraction that is fresh water, they became more thoughtful. Six milliliters of that 30 is all we have for fresh water that isn’t frozen. And finally, to represent the 0.003% of water on Earth that is fresh, non-frozen, and above-ground, I let a single drop fall into the bottom of a tin cup. For once, they were quiet enough that even the back of the room could hear the soft “plink.”

My spring visit to the sixth graders is always a little bittersweet, because our MuseumMobile visits don’t follow them into seventh grade. It’s exciting to share bar graphs of the data they collected about goldenrod galls, and to reinforce the notion that they are young scientists. Now that I’ve been at the Museum for seven years, my history with these kids goes all the way back to kindergarten. We started out together by exploring nature with our five senses, and we culminated by using tools and collecting data. After seven years, they are just as curious and excited about nature as they ever were. While their chorus of “thank you!” followed me out the door, I hoped that never changes.

Special Note: Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Bee Amazed!” opens on May 1, 2018.

Friday, March 9, 2018

Sweating through the Birkie

This winter I think I’ve skied more kilometers than ever before. A combination of consistent snow conditions and high motivation levels for doing my best in the American Birkebeiner ski race led me out on the trail more often and for longer distances than usual.

My training sessions were mostly solo, although a couple pairs of vociferous ravens often kept me company at the North End Ski Trails. Scolding chickadees were ubiquitous and always improved my mood on a long climb. When a barred owl made an appearance, its flight was so silent that it seemed to make the whole woods go quiet. While I never saw a live, wild mammal, the tracks of wolves, foxes, fishers, squirrels, and voles still felt like good companions. Deer tracks scuffing up my classic tracks were less appreciated. Cold days brought the metallic smell of snow. Warm days wafted the smell of damp bark under my nose. Stark patterns of black and white, with purple shadows and deep green trees dominated my view.

After all that solo time, the scene at the start line of the Birkie was quite a shock. A rainbow-colored sea of people milled about on the snow. Music and the announcer’s voice blasted from the sound system. Cheering erupted at the sound of each shotgun start. The smell of porta potties came and went on the slight breeze. Skis and poles were everywhere.

I took my place among the crowd of fifth-wave skiers, and as we flew into action at the sound of our start, the snow in the tracks felt silky smooth under my skis. In a fluid chain, we wound up, down, and around rolling hills through the woods. I hoped that other skiers were also appreciating the way the smooth drifts sparkled among dark stripes of trees in the bright sunshine. It was a beautiful morning.

It was also warming up quickly. I’d been able to force myself to start in light gloves despite the chill in the air at start time, but I hadn’t convinced myself to remove the magnetically attached sleeves from my jacket and thus start in just a vest. My fingers went from numb to happy in just the first kilometer, and then my body temperature just kept climbing.

I’m probably the only person who thinks about moose at a time like that, but several years ago I learned that those massive mammals feel heat stress anytime the temperature climbs above 20 degrees in the winter. Their hollow, insulating hairs and huge body mass (1,000 pounds easily), are well-adapted to keep them warm. While I can’t quite empathize with their bulk, I do understand how they easily overheat in a warm coat. Many of my friends have chuckled or shaken their heads at the minimal layers I wear skiing (just a base-layer and my thin jacket even below zero), and multiple moms have cringed at my reluctance to wear a warm hat.

Unlike moose, though, I can don or doff my warm winter layers pretty easily. Which is what I did when I reached a wide spot in the trail.

No amount of taking off layers could have kept me cool on the long climbs leading up to the High Point, though. Hot sun beating down didn’t help. I could feel sweat running down between my shoulder blades and beading up on my forehead.

All that sweat brought to mind a podcast I’d listened to recently—a TED Radio Hour on the theme of adaptations. Chris McDougall, author of the book Born to Run, was the guest, and he shared his theory that long-distance running, especially in heat, was our superpower. Our lack of body hair and our numerous sweat glands allow us to sweat better than any other mammal on Earth. “It was that ability to sweat which made every other great human achievement possible, because the fact that we could sweat allowed us to run super long distances on hot days,” claims McDougall.

Of all the theories about how humans evolved to be the way we are, I think this is one of my favorites. My aptitude for sweating connects me to the success of humans in evolutionary history. Adaptations don’t just include physical traits, though, and cross-country skis are a great example of humans’ ability to make tools and adapt to a wide variety of habitats. The Birkie combines these two adaptations seamlessly as thousands of people “run” on unique tools, for a long distance, over snow.

After crossing the International Bridge, I smiled all the way up Main Street in Hayward to the finish line. A volunteer was waiting there to put a finisher’s medal around my neck. We both grinned.

A couple days later, after it no longer hurt to climb stairs, I headed back out to my beloved trails. The ground flew by beneath my skis and a light breeze kept me cool. Chickadees sang. What a joy it is, to use my adaptations.

Special Note: Columnist Emily Stone is publishing a second book of her Natural Connections articles as a fundraiser for youth programming at the Cable Natural History Museum. Since community members are often the inspiration for her articles, the Museum is conducting an art project for kids and adults to illustrate each chapter with a black-and-white line drawing. Find the details and entry form at

Friday, March 2, 2018

A Winter Walk with Lois Nestel

Curtains of snow sifted down from the laden trees as we entered the forest. The wizened branches of the Grandmother Tree, an old white pine, etched black and white silhouettes against the low, gray sky. Smooth new drifts stretched out in front of our little group of children and adults on the Family Snowshoe Hike.

The Wayside Wanderings Natural Play Area is a special place in any season, but in the magic of a fresh snow, I felt Lois Nestel’s presence more keenly. Lois was the founding naturalist, director, and curator of the Cable Natural History Museum. She was a talented, self-taught naturalist, artist, and taxidermist, and this was her home site. She looked out into this forest on moonlit nights and wrote about the owls that hooted and the rabbits that cavorted in the moonlight.

Lois once summed up snow this way: “However you see snow, as a burden to be borne or as a base for winter sports, see in it also the incredible beauty beyond the power of man to duplicate or even to describe.” Being in her forest on such a lovely day inspired me to look back on some of Lois’s essays.

“Winter has a thousand faces;” observed Lois, “each of us is free to see the face we choose. For example, the colors of winter are subtle and transient. Nothing is as it seems. The snow is white, it is true, but it is also endless hues and shades depending on the light, the type and quality of snow, and even more on the eye of the beholder.”

“Under leaden skies the snow appears dead white or pearly toned with shadows that are slate and steel. Sunrise can turn open spaces to rose and palest gold shadowed with lavender and violet; mid-day brings the clearer blues, and the evening sky may add a depth of tone to morning hues.”

“Frost flakes caught in morning sun outshine the jewel treasures of the world as prismatic reflections bedazzle the eyes with brilliant sapphire, topaz, emerald, and ruby that change with every movement and finally fade with advancing day, as do the rainbow-tinted sundogs that accompany a chill morning sun.”

“Moonlight on the snow brings shadows traced in indigo against the cold white flame of diamonds. The blue-black velvet of the night sky, studded with cold, blazing stars will often show the aurora borealis as wavering, tattered banners or as moving spotlights against the northern sky,” wrote Lois.

We didn’t see the aurora on our hike, of course, but we did see deer tracks, woodpecker trees, and the delicate, snow-laden cup of a birds nest. The woods were full of patterns.

“Most people are aware of the beauty of summer flowers and often bemoan their passing as winter approaches,” Lois continued. This need not be a cause for regret because, while much color may be lost, there continue—as seeds, pods, and capsules—many forms that rival the flowers in beauty and grace. Many of these seed containers last throughout the winter, serving as food for wildlife and pleasure for humans.”

“There is a sculptured beauty in the pods of various milkweeds and wild iris, evening primrose, cockle and Indian pipes. Delicate grace is exemplified in airy sprays of sweet cicely, papery clusters of wild hops and feathery virgin’s bower (wild clematis) twining over bushes, and in the dried grasses and sedges, each with individual form and style.”

“Many fall-blooming flowers (weeds if one must call them that) retain their form if not their color through the winter months. Goldenrod, tansy and yarrow are sepia-toned replicas of summer’s gay colors. Flowers such as asters lift clusters of tan, star-like sepals above the snow.”

“Touches of color do remain in scattered places; the dark velvety red of sumac heads, the red-orange of rose hips and the brighter red of highbush cranberries and hawthorn frozen on their shrubs.”

“To enjoy these and many other beauties of winter there are few requirements; namely these: get outside, have open eyes to see and an open mind, receptive enough to appreciate what is seen.”

Special Note: Columnist Emily Stone is publishing a second book of her Natural Connections articles as a fundraiser for youth programming at the Cable Natural History Museum. Since community members are often the inspiration for her articles, the Museum is conducting an art contest for kids and adults to illustrate each chapter with a black-and-white line drawing. Find the details and entry form at

Friday, February 23, 2018

Making Tracks on a Snowshoe Field Trip

Awooooo! My best impression of a wolf howl rose over the crunching of snowshoes and little voices. Gesturing to the group of third graders from the Hayward Intermediate School, I invited them to howl back. The choir that responded sounded nothing like wolves, but it was music to my ears nonetheless. So was the expectant silence that followed, since these kids were wise to the fact that I’d howled to get their attention.

“We’re going to hike like a pack of wolves today,” I declared. “Do you know how wolves walk when they’re in deep snow?” I led this same snowshoe hike four times over the course of two days, and in each group there was one outdoorsy kid who knew. Wolves walk in a single file line and step precisely in the footprints of the wolf in front of them. The kids understood the benefits of the wolves’ behavior intuitively. Who hasn’t made their own life easier by following in someone else’s footsteps through deep snow? 

“I’ve tracked wolves,” I told them, hoping to establish credibility. I’ve followed a trail that looked like it was made by just one wolf going through deep snow. When it came to a ski trail, though, the wolf tracks fanned out on the firm surface and I counted at least six in the pack.

With one last admonition to walk in a single file line, I howled again, and they howled back as we started up the trail.

The Mammal Tour on the Ridge Trail is a wonderful community resource. The 1.1-kilometer loop trail is the easiest of several snowshoe trails at the North End Trailhead just south of Cable, Wisconsin, and the Museum and our partners have created a self-guided interpretive trail along its length. We started out with plywood mammal silhouettes cut by the Drummond High School shop class, but hungry porcupines rendered most of those unrecognizable after just a few years.

This past fall, a funding drive spearheaded by the North End Ski Club and community member Ron Caple made it possible for us to commission a set of 25 new metal mammals cut by Mark Blaskey in Altoona, Wisconsin. We reprinted the booklets, too, which contain drawings, information, and tracks for all the mammals, plus a map of the trail. In January, attendance at our Backcountry Film Festival helped offset the cost of hosting this field trip.

I hiked the kids right past the shapes of a woodchuck, a big brown bat, and a chipmunk. When we finally stopped between the wolf and the deer silhouettes, I asked if they could guess why we skipped the other mammals. At least one student was paying attention. “You told us we were just talking about animals that stay active in the winter. Those animals don’t.” Haley Appleman, the Museum’s naturalist, was just then back in the Museum’s education room with the rest of their class talking about animals that migrate and hibernate. Out in the woods, we wanted to think about how animals confront the cold and snow head-on.

Wanting to wow them with the thickness of a wolf’s fur, I walked over to one of my helpers—a third grader carrying a heavy orange backpack. When I unzipped the pack and started pulling out a huge wolf pelt, a wave of surprised comments rippled outward. The helper was the most surprised of all. “You mean I was carrying that on my back!?”

Our next stop was below the form of a flying squirrel on the tree. Unlike wolves, they don’t have thick enough fur to sleep out in the open. For warmth, flying squirrels huddle together with their friends in a hollow tree. Handing out durable thermometers to small groups of kids, I challenged them to see how much heat they could generate by huddling together with their friends. Most groups brought the temperature up to 40 or 50 degrees, but one group of girls used their breath and registered over 70 degrees!

Down the trail, we compared the squirrel’s simple shelter to the more elaborately constructed lodge of a beaver. Even though we never see beavers in the snow, they are able to stay active all winter by snacking on their store of twigs under the ice and resting snugly in their lodge.

By far, though, my favorite topic to cover on any winter ecology hike is the subnivean zone. This magical space opens up at the boundary between still-warm earth and the insulating blanket of snow. Here, mice, chipmunks, voles, shrews, spiders, ticks, fungi and bacteria find their own special shelter.

As mysterious and invisible as this space is to us humans, however, a whole suite of predators have learned to access its rich stores of prey. Skinny weasels follow chipmunks into their burrows. Alert foxes and coyotes cock their ears toward scurrying mice and pounce through the snow. Vigilant owls’ precise hearing guides them to punch through the crust with bony talons and grab a late-night snack.

At our final stop on the trail, I invited the kids to explore the subnivean zone, too. In place of deadly accurate ears, I hand them mini-Frisbees I call “treasure finders.” Give it a toss, watch where it lands, then dig down. The Frisbee knows where treasures hide in the subnivean zone—which, of course, is everywhere. Every leaf, stick, acorn, or bit of moss is a treasure to some resident of this forest.

“Awoooo!” I called again, and “Awoooo-oo-oo!” my wolf pack replied as we began the last stretch of their hike back to the bus. With the end in sight, tired legs were forgotten and the group’s chatter turned to comments like “that was so fun,” “we hiked so far,” and “I wish we could go farther.” This, of course, was music to my ears.

Special Note: Columnist Emily Stone is publishing a second book of her Natural Connections articles as a fundraiser for youth programming at the Cable Natural History Museum. Since community members are often the inspiration for her articles, the Museum is conducting an art contest for kids and adults to illustrate each chapter with a black-and-white line drawing. Find the details and entry form at

Friday, February 16, 2018

Witches' Brooms and other Ski Trail Observations

This time of year, most of the nature I observe is along the cross-country ski trails in northwestern Wisconsin. Just a few days ago, I skied over a string of fresh red fox tracks. Occasionally a strong skunky odor accompanied them, and I looked a little closer to see which unfortunate pine seedling had been scent-marked. The tracks zig-zagged in and out of the woods, and eventually culminated in a fox-track party! This is the peak of their breeding season, so activity levels are high.

In among the fox tracks I started noticing foot prints from the fox’s largest cousin. Gray wolves are not uncommon here, and ski trails are some of their favorite highways. Wild animals enjoy easy travel as much as the rest of us because it helps conserve their hard-won energy. This particular gray wolf must have been eating well, because he also left a huge pile of scat right next to the ski tracks.

On a different ski, I spotted a tiny shrew frantically scurrying across the smooth snow of the skate-ski lane. When it reached the two parallel canyons of the classic tracks, an awkward scramble ensued to get itself up and over the humps. I chuckled at how different the world must look to each of us. Then, when it tunneled through the top skim of fluff just off the trail, I blinked in awe as it vanished. I’ve seen the results of this surface tunneling before, and always shook my head at how a little critter could think that nosing through just the top layer of flakes could hide it from the eyes of a watchful predator. I stood corrected…and alone…in the woods.

Sometimes I ski right past curiosities countless times before finally noticing them. That happened recently after I encountered friends on the trail who had a question. “What’s up with that big clump in a pine tree over by the second place the North End Trail crosses the Birkie Trail?” asked Irv and Jan Berlin. So I made a point to look up on my next loop out there, and then sent a photo to Paul Cigan, a Wisconsin DNR Forest Health Specialist, for his input.

“Cool find!” he replied. “I think I might have seen that very witches’ broom while out skiing.” Paul went on to explain that anything that kills a growing tip on a tree can instigate a thicket of new shoots that (if you use your imagination) looks like the business end of a broom. The name was coined in medieval Europe, and their homemade twig brooms bear an even stronger resemblance.

While anything from fungi to mites, mistletoe, bacterial parasites, and environmental insults can cause witches’ brooms, the most common initiator on pine trees, wrote Paul, is actually just a mutation of their own cells. An accident during cell division can result in an abnormal number of chromosomes in meristematic cells. Similar to a human stem cell, plant meristems are undifferentiated cells that can become a variety of different types of tissue. When dysfunctional meristem cells die, other shoots jump in to take their place. Or perhaps the meristems keep growing, but not in a normal way.

Because this witches’ broom is likely due to internal error and not a pathogen, it’s not at risk of infecting its neighbors. It might have a small negative impact on the tree itself, though, by sucking up nutrients that could be put to better use elsewhere in the tree. Paul speculated that “the one at the North End is moderately large and I would expect that it is reducing height, stem, and overall crown growth.”

On the other hand, some brooms have been observed to produce viable seeds that grow into dwarf trees. Humans have discovered that grafting a twig from a witches’ broom onto a normal rootstock can result in weird trees that collectors enjoy.

Sometimes, witches’ brooms can even play a positive role in the ecosystem. A type of moth uses the dense thicket to feed and shelter their larvae. Other critters, such as flying squirrels, might use them as a nest.

Fox tracks, wolf scat, mammal burrows, and witches’ brooms…what will I ski past next?

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: "Better Together--Celebrating a Natural Community" is now open!

Friday, February 9, 2018

The Great Migration of Miniscule Things

Time was running short. Dave Neuswanger, a retired fisheries biologist, had led such a fascinating discussion about winter limnology (limnology is the study of lakes), that the afternoon program of our Master Naturalist workshop was behind schedule. As we gathered boots, coats, and a digital meter that measures both temperature and dissolved oxygen, I suggested we bring the plankton net, too, and combine trips to the hole through the ice on Lake Namakagon. Dave hesitated, and gently reminded me why we hadn’t combined these data collection forays on the schedule in the first place: the critters we wanted to find just wouldn’t be near the surface in broad daylight!

Dave Neuswanger lowers the probe to test dissolved oxygen and temperature at 2-foot increments in Lake Namakagon while Master Naturalist students look on. 

Here are the results from our DO/Temp probe: Lake Namakagon has pretty hi dissolved oxygen almost all the way down to the bottom! That's a good sign for fish.

Many types of zooplankton (which are mostly microscopic animals in lakes and oceans) participate in a cycle where they swim up to the surface at dusk and descend to the dark depths again at dawn. Scientists call this diel vertical migration (DVM). The word diel comes from the Latin word for day, and refers to a 24-hour period.

Such a great number of tiny organisms exhibit this behavior that Professor Hays of Deakin University in Australia wrote “DVM in ocean zooplankton is likely to represent the largest daily migration of animals on Earth, in terms of biomass.” The DVM was discovered during World War II, when the U.S. Navy was using sonar to watch for enemy submarines. A dense group of zooplankton, moving in sync through the water column, scattered their sonar so much that it looked like a false bottom in the sea.

On our second, later, visit to the lake, I wasn’t sure what we’d find as Dave pulled our fine-mesh plankton net up out of the hole. We all cringed as he used bare hands to coil the net’s wet line. A pink sunset was just fading over the hills around Lake Namakagon when we trudged back to shore though soggy snow.

While the Master Naturalists munched on appetizers, Dave concentrated the sample and I set up the Museum’s new digital microscope. Just as we were getting antsy and students started to fill their plates with baked ravioli for dinner, Dave brought over a small porcelain cup filled with lake water. Careful not to spill, I set it under the microscope and fiddled with the focus wheels. Onto my computer monitor jumped a school of darting critters. Excited now, and wanting to share, I plugged the projector cord into my computer. A cheer of excitement rippled through the group as larger-than-life aliens scurried across the screen at the front of the room.

Almost all of the swimmers were daphnia. You may have seen these mini-crustaceans before, in a high school or college biology lab. Through their translucent carapace, it is easy to view the daphnia’s heart beating and blood cells flowing. They react quickly to alcohol and caffeine, so students can easily quantify the effects these substances have on a daphnia’s heart rate.

We didn’t want to torture these critters, though, just admire them. Roughly oval in shape, daphnia have a single large eye at the front of their body, along with two pairs of delicate, branched antennae. It is the second, larger pair of antennae that drives their movement, especially the sideways jerky hops that earn them the nickname “water fleas.” Despite their ability to move short distances, on a larger scale daphnia are at the mercy of strong currents, and tend to avoid them. Daphnia’s many legs are used to create their own, personal current that drives food through their carapace so they can filter feed.

This ability to convert bacteria, algae, and fine detritus into fish food makes daphnia an essential part of many aquatic food chains. (The mass exodus of zooplankton from surface waters during the day must be a huge boon to their phytoplankton prey who can then photosynthesize in relative safety.) Although any organism’s role in the ecosystem includes eating and being eaten, it’s also their evolutionary prerogative to maximize the first and delay the second. That’s where the diel vertical migration (DVM) comes in. Daphnia (and other zooplankton) are highly visible to fish in daylight, and sunrise triggers them to escape by fast downward swimming, not simply by sinking. Fast-swimming daphnia are more conspicuous, but for a shorter time, and escape the brightly lit, risky, upper waters faster.

Once they’re at depth, beyond the reach of sunlight, though, how would the daphnia know that dusk is falling? Scientists hypothesize that they use an internal clock, run by their single eye. Pigment in their eye changes over time, so their migration is synchronized by light at dawn and triggered by biology at dusk. While light is the main factor in their movements, DVM is expedited when the critters can smell fish nearby. The fish smell is a result of chemical substances called kairomones. This fancy word just means that what the fish give off is detected by a different species, who gains some sort of advantage from it. (In contrast, pheromones are detected by an animal of the same species.) In murky water, these chemicals may actually be a more important trigger of DVM than light.

Several Master Naturalists agreed that watching the daphnia swim under our microscope was better than TV. In the end, we were glad we’d gone back out at dusk to sample plankton, even though it delayed our dinner. Happy and exhausted from our long day of discovery, we participated in our own diel migration—going home to bed.

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: "Better Together--Celebrating a Natural Community" is now open!