Let the Sleeping Bear Lie

After my article about bear hibernation a couple weeks ago, several readers wrote to share their amazement at bears’ incredible adaptations for hibernation. I’ve been looking for an avenue to write about bears for some time, which may be part of the reason I overlooked some additional very important information about bear hibernation, and may in fact have stressed out the very creature who I’m so enthralled by. I was grateful for a very thoughtful letter from Ken Jonas, a recently retired DNR wildlife biologist, who offered some cautions, and some additional important information about bear hibernation. I want to share it with you all, too, because I think my previously casual attitude about disturbing a challenging time in a bear’s life is common among people in the Northwoods.

One of the key aspects of hibernation is a decrease in bodily functions like metabolism, heart rate, breathing rate, and body temperature. While bears have a unique ability to stay warmer and wake up faster than some other, smaller hibernators, that does not mean that waking up has no consequences for them. As a bear’s fight-or-flight mechanism revs up in response to some disturbance, all of those body functions increase and a portion of their limited energy stores are used up.

While this may not be a significant problem if it only happens once, repeated disturbances can cause a bear to deplete its energy stores to a dangerous level. During one study of hibernating bears, researchers discovered that the bears’ heart rates increased as soon as a human approached and remained elevated for several days after even minimally invasive visits. Who knows how much stress a barking dog causes (Hunter has been kept away from the area since he first found the den), or even a few humans with a flashlight and cameras?

Although many who visit the Northwoods in the summer are concerned about having a bear encounter in the woods, it is actually the bears who are deathly afraid of humans – especially at close quarters – according to Ken. He wrote: Although hibernating bears “usually have the response to just stay put and hope for the best…They’re still scared as heck, with all of the measurable physiological responses that go along with that condition.”

Ken also informed me that excavated and underground dens, similar to the one I visited, are typical of pregnant female bears. While it is exciting to think that my friend might have cubs near his house in the spring, it is also worrisome. The consequences of disturbance are even more serious for a mother bear. This is the time of year when cubs are being born. Not only are the mother’s fat stores especially important because of her need to feed the cubs as well as herself, disturbance can sometimes lead to den abandonment. Ken wrote, “Relocating to a new den in the midst of winter has a huge energy cost for any bear. If it is a sow with newborns she may not come back for them, in which case they definitely will not survive.”

Now, while we three naturalists who visited the den did so only out of our affection for and fascination of bears, according to the information provided by Ken, this may have been a pretty selfish act. In the field of outdoor education, we often discuss the cost/benefit ratio of various activities that might cause some harm to a single organism or section of a forest but result in significant teachable moments or an increase in affection for nature in the next generation. Sometimes the benefits outweigh the costs and we allow kids to participant in mildly destructive hands-on learning. In hindsight, I’m not so sure that the potential costs of our den visit were justified.

Hopefully, by sharing my newfound knowledge with you, we can all use this as a learning experience. While no one I’ve talked to up here has advocated for repeatedly bothering a hibernating bear, I’ve gotten the impression that most people don’t think twice about a single visit. And while Wisconsin law says that no person may harass protected wild animals (which includes bears), the consequences of even small disturbances to a hibernating bear are not prominent in the DNR’s web resources. Now that we know, we can respectfully keep our distance and let the sleeping bears lie.

 “I think that is the story people need to hear – leave winter wildlife alone, it is the most difficult time of the year for them in terms of survival. We should not be adding to their stress for our own selfish purposes.” – Ken Jonas

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Lake Alive!” opened May 1, 2015, and will remain open until March 2016.

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.

Scatology

“Ewww!!!” exclaimed the second graders as I pulled a large rubber replica of bear scat out of the tub. Scat, of course, is the scientific word for animal poop, and we were about to become scatologists.

During my fall MuseumMobile visit to their classroom, we’d talked about the different adaptations that herbivores, omnivores, and carnivores need to survive. We examined beaver and deer skulls to see the flat, grinding teeth that herbivores need in order to eat plants. Next, the jagged, pointy back teeth and long, sharp canines on the wolf skull created quite a stir. Students had no problem imagining how those intimidating teeth help the large carnivore survive. Then we omnivores ran our tongues over our own canines and molars, and connected our mixed diet with that of a bear.

Today, during the winter MuseumMobile visit, I wanted to carry that theme a little farther, a little deeper, to its natural end. Hence the replica bear scat. “Take a look at the Animal Scat Identification Chart in front of you,” I instructed. The chart is divided into three columns, one each for herbivore scat, carnivore scat, and omnivore scat. I had the kids look for shared characteristics among the herbivore scats. The words small and roundish seemed to summarize their ideas. The carnivore scats were all long and thin, with tapered ends. I explained that those tapers are usually shaped by hairs from the prey animals. The omnivore scat was somewhere in the middle. The cylinders were much longer than herbivore scat, but had blunt ends instead of the hairy points.

“So who do you think made this scat?” I asked, while holding the handful of rubber bear scat aloft. Several hands shot into the air. Omnivore. That was an easy one. Next, I pulled out a replica of scraggly fox scat, and a pile of rubber deer scat. No problem. Most kids were confident that they could categorize any scat the might find in the woods.

Identifying scat to species is a little more difficult though, since many related animals produce similar scat. The size of a scat can be somewhat helpful, but that can vary quite a lot among individuals of the same species, and even in one individual from day to day. For example, fox scat and wolf scat can overlap in diameter. The contents (if you’re brave enough to look closely), can also be a clue. Otter scat is often chock-full of crayfish shells and fish scales, but many animals have a widely varying diet that can produce very different-looking scats.

In some cases, it is pretty easy to narrow down certain shapes of scat into groups of related animals. For example, rabbits, hares, and pikas (all Order Lagomorpha) poop in piles of flattened spheres, not unlike sawdust-filled M&Ms. Deer and their relatives produce slightly elongated spheres of various sizes, often with a point on one end and a dimple on the other.

Members of the dog family have the long, tapered cords. Other carnivores are similar, but with interesting quirks. Cat scat tends to be broken into segments, or at least constricted in a few places. Weasels tend to have dark, greasy cords that loop back on themselves, and they like to place it in the middle of the trail, especially on a prominent rock.

The weasels’ choice of latrine location hints at one of the several purposes of scat. Of course, it is first and foremost a way to get rid of waste. Scat is also an important form of communication among animals. It marks a territory, announces a presence, and can sometimes relay the receptiveness of a female during breeding season, too.

For humans, scat can add interesting information to a tracking expedition, indicate what animals are nearby (though both the scat of the predator and the evidence of its prey still in the scat), and provide some giggles, too. Scientists use scat to get DNA specimens, sample stress hormones, discover details about diet and health, and study the abundance of animals in a population. Collecting scat is often a cheaper, safer, and less stressful way to study an animal.

One by one I pulled several other scat replicas out of my tub. One boy in particular had a knack for categorizing them, and shouted answers gleefully across the room. A girl just shook her head in confusion. She couldn’t see the pattern, and probably didn’t want to look much closer anyway.

Scatology is a fascinating subject with many benefits for amateur naturalists and scientists alike, but I will admit – and you might agree – not everyone is cut out to be a scatologist.

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Lake Alive!” opened May 1, 2015, and will remain open until March 2016.

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.

The long, thin cord of a carnivore's scat ends in a tapered point.  You can learn a lot from scat. Photo by Emily Stone

The long, thin cord of a carnivore's scat ends in a tapered point. 

You can learn a lot from scat. Photo by Emily Stone

The Bear Necessities of Hibernation

A warm, musty smell hovered around the den’s entrance. By shining a flashlight into the hole, we could just make out a thatch of thick, black fur behind a screen of tree roots. Kneeling awkwardly on the snow, we each took turns trying to reach our cameras into the opening for a better angle. It wasn’t until I uploaded the photos at home that I noticed the single brown eye staring back at me through a gap in the roots. Peekaboo!

For many years, scientists have wrestled with the question of hibernation, and if bears are “true hibernators.” One of the sticking points, it seems, was bears’ ability to wake up quickly during the winter, and be immediately active. The unquestioned hibernators – like ground squirrels – get so cold that they must warm up a bit before they can move quickly. A ground squirrel would probably not have opened its eyes in response to my camera flash. The bear did – and then promptly rolled over to go back to sleep. Subsequent photos just show an expanse of back fur.

Hunter, the 12-year-old German shorthaired pointer who discovered this den, experienced the bear’s relatively light sleeping, too. By the time his human arrived at the scene of a commotion, the bear’s growling snout was partway out of the hole. Luckily for old Hunter, the bear didn’t deem him enough of a threat to exit any farther. Still, having the option to defend yourself in an otherwise vulnerable time is an incredible advantage for bears. Chipmunks hibernating under the snow may never wake up if a weasel comes knocking. They become lunch before breakfast. 

As scientists learn more about the winter physiology of bears and other hibernators, they’ve had to refine the definition of hibernation. While it used to focus on animals that show a significant drop in body temperature, the emphasis is now on a specialized, seasonal reduction in metabolism concurrent with scarce food and cold weather. What’s more, scientists recognize that hibernation is on a continuum with the short-term bouts of decreased activity known as torpor. Not only have bears been restored to their place of esteem as hibernators, but many scientists consider them super hibernators.

Amazingly, black bears generally do not eat, drink, defecate, or urinate during hibernation. They subsist off the 30 percent extra body fat they acquired during the fall feast. Even though this high-fat diet causes a doubling of their cholesterol levels (a serious problem for humans), bears do not experience gallstones or a hardening of their arteries like we would. In fact, we can use a substance secreted from a bear’s liver to dissolve our own gallstones without surgery. Urea, a potentially toxic waste product created during the metabolism of fat that would typically be flushed out with water, is broken down into protein and used to build the bear’s lean muscle. Additionally, despite the long period with no weight-bearing activity, bears do not lose bone mass. Once scientists figure out the mechanism that keeps bears’ bones strong, we may have a new miracle cure for osteoporosis.

A hibernating bear’s breathing slows significantly, from 40 breaths per minute down to eight. This is matched by a 50-60 percent reduction their metabolic rate. Nevertheless, bears’ huge bulk and thick fur enable them to stay within 12 degrees Fahrenheit of their normal 100-degree body temperature. The den’s small opening, snug fit, and a layer of duff on the floor also help them retain heat, although bears are commonly found hibernating in relatively unprotected places as well.

In contrast, ground squirrels and chipmunks let their body temperatures drop to just above freezing. Virtually no normal functions can continue, and so they must wake up every week or so to warm up, move around, urinate, eat, and experience deep, refreshing sleep. Bears can wake up, but they don’t have to – unless, of course, a nosey dog and his people come sniffing around.

We don’t know for sure when this bear entered its den, but hibernation is usually triggered by a combination of weather and lack of food. With this year’s late-coming snow cover, bird feeders were getting raided much later than usual, since bears were in no hurry to den up. One researcher observed that the final den entry often occurs during a snowstorm so that fresh snow will hide any signs that could lead unwanted guests to the sleeping bear.

Indeed, no bear tracks marked the snow near the den’s entrance – just the prints of one snoopy old dog and a few curious naturalists interested in seeing a super hibernator in action.

Bears are able to maintain a high enough body temperature during hibernation that waking up to check on unwanted visitors is a relatively quick process. Photo by Emily Stone.

Without the aid of Hunter (not pictured) we probably never would have found the den. Photo by Emily Stone.

A Hike with Auntie Em

“When can we go on a hike with you, Auntie Em?” asked a six-year-old in a shark costume after all the Christmas presents were opened. Those may be the sweetest words I’ve ever heard. After a flurry of finding boots (here’s one, where’s the other one?), digging grubby old jackets out of the closet, and tugging mittens over small hands, we were off!

With the first big snowstorm still just part of the long-range forecast, we stepped out into a brown world under a blue sky. Zac spotted some pretty flower seed heads and wandered into the restored prairie to pick some for Grandma. “Here’s one of those balls!” he shouted, grabbing a goldenrod gall from among the flower stems, “And it has a piece of corn in it!”

We examined the gall together. Along the equator of the small, brown globe, a downy woodpecker had used its needle-sharp beak to peck a neat hole and extract the sweet, juicy fly larva. Wedged into that hole was a hulled sunflower seed from the bird feeder. This was surely the work of a black-capped chickadee. Those energetic little year-round residents cache as many as 100,000 food items per year – most of them in the winter when food scarcity is a serious risk. In order to remember all of those caches, chickadees add new neurons for every hidden seed, berry, or insect. The result is a 30 percent increase in brain volume, which shrinks again during the easy-living days of summer.

Zac has always had a larger than average head, and I could see it expanding just a little more to accommodate this new bit of information.

Thawing dirt squished under our feet as we turned from the driveway onto the minimum maintenance road at the end of the driveway. The old road was cut deeply into the ridge, with high banks rising on either side. This put cushions of moss at eye level for inquisitive minds. Drawn to the vivid green, Zac got his nose right up into the living carpet. A boy after my own heart. “Helicopter!” was his first discovery, as he grabbed the tiny maple seed.

First he tossed it up, and we marveled at its whirling descent. Then I picked it up and added several feet onto its launch. Zac’s eagle eyes followed the seed into the leaf litter, so we had one more launch. This time, we passed the seed up to Zac’s twin, Kylee, who had scrambled up to the top of the road cut. Three heads nodded in unison as we tracked the spinning seed. Wasn’t I just saying how nicely maple seeds are designed for human play?

This time, the seed landed near a branch; a long, skinny branch, with a hooked tip, that caught Zac’s eye. Both twins worked on getting the gangly tool vertical, and then Kylee backed off and gave orders. “Pull down a tree!” she encouraged, as Zac struggled to hook the stick over low-hanging twigs. Up, up, up, he reached, with his every move exaggerated into wide circles at the top. Finally, Kylee couldn’t stand it, and she joined in to help. With four hands, the hook stayed steady, and finally they got it over a small branch. Who needs plastic toys when you have sticks?

As we detoured off the road onto a deer trail, my pockets began to fill up. Zac picked up snail shells, squirrel-sculpted walnut shells, a rodent-chewed chunk of deer bone, and a dozen other trinkets for me to carry back and show Grandma. Young eyes zeroed in on splashes of color in the drab woods. We examined turkey tail fungi coated in bright green algae, discovered a scarlet cup fungus under the maple leaves, and marveled at a stump capped with tiny dots of lemon drop cup fungi.

Then we found a log populated by puffballs. Once I had demonstrated the effects of poking the deflated brown ping-pong balls, the kids took over. Their small fingers ejected clouds of olive green spores into the breeze. This assistance with spore dispersal was exactly what the fungi were hoping for! Although I don’t usually bring up scientific names with kids, I just had to tell them that the genus of this mushroom means “wolf-farts.” We all giggled before moving on.

The deer trail took us down into a small ravine, where several fallen logs bridged the gap. Kylee, gymnast that she is, headed straight for the first mossy balance beam. I scrambled into the dry creek bed to catch her, but I needn’t have. Zac took the more conservative route, and scooted across another log on his rear end.

Climbing and jumping off banks, poking at things, and swinging off tree trunks, we made our way back to the house. Zac picked up his bouquet of dried flowers and looked up at me with big brown eyes. “We earned our hot chocolate today, didn’t we Auntie Em?” Yes, Zac, we sure did!

Scarlet cup fungi fruit on rotting wood in the cool days of winter and early spring. Photo by Emily Stone.

Zac and Kylee helpfully assisted with the puffballs’ spore dispersal, using their small fingers to send clouds of olive green spores into the breeze. Nature provides endless entertainment for kids of all ages. Photo by Emily Stone.

Helicopter Seeds

A few snowflakes tumbled and drifted their way down as I opened my bedroom window. The fresh air felt good, but that wasn’t my goal. I was feeding the birds. In order to give my chickadees consistency throughout bear season, I have a small feeder suction-cupped to my second story window. I can tilt out the pane of glass and reach over the top to fill the feeder with sunflower seeds. Even while the bears are asleep, I like the alarm clock services that the chickadees – as they peck noisily on seeds and gargle at each other – provide.

As I swung the window shut, the motion dislodged a maple seed that must have been stuck on the outside of window frame. Already feeling child-like and giddy from wrapping Christmas gifts, I pressed my nose to the window and eagerly watched the helicopter spin its way to the ground. The sight brought back a flood of memories – not just from the handfuls of maple seeds we tossed into the air as kids, but also of the very playful college freshmen who studied the seeds during a botany lab I taught in graduate school.

Maple seeds are exquisitely designed for both human play and the trees’ reproductive fitness. Their spinning flight is not only fun to watch, but it also allows the seeds to disperse up to a mile away from their parent tree, out from under its oppressive shade.

These magical seeds develop from tiny spring flowers. Nose-to-nose, with their rooster-tail wings arching away, two seeds start off in a pair. Each seed holds the key to future generations, and it also holds the key to flight. The heavy seed carries enough energy to produce a root that can penetrate through the maple’s own thick leaf litter.

Without much wind, my windowsill maple seed spun almost straight down and disappeared into the soft snow. With a terminal velocity of about 3 meters per second (about 6.7 miles per hour) it was a quick trip. At the end of its flight, the structure of the seed and wing becomes more like a dart – drilling the seed into the substrate to find it a secure place for germination.

But the center of that useful mass is not at the geographical center of the seed. This asymmetrical distribution of mass is one of the essential ingredients in the helicopter seed’s flight. Even broken samaras (samara is the technical name for these winged seeds) with barely any wing left can spin and generate some lift.

When you add the wing off to one side, the center of balance becomes even more lopsided. Part of the seed’s role is to counterweight the papery wing and make sure that the wing is oriented for maximum lift as it spins. The wing itself is elegantly designed with a slight pitch (like a fan blade), that facilitates the spin. As the wing – tapered at both ends – spins around the weight of the seed, the air rushes fastest over the wide main blade, increasing the lift, while the narrower outer tip cuts through the air with less drag.

As the wing spins, its leading edge generates a horizontal, tornado-like vortex that lowers the air pressure over the upper surface of the wing, effectively counteracting gravity and doubling the lift in comparison to non-spinning seeds. The spiral motion is resistant to disturbance by wind, so the lift it generates can allow the wind to help disperse the seed farther.

Some helicopter seeds are better at sustaining flight than others, though. That’s what we tested in the botany lab. Students calculated the surface area and weight of each seed. The ratio between the two measurements is known as “wing loading.” Then students stood on a table and dropped the seeds one by one, while a research partner timed the descent. Seeds with lower wing loadings tended to stay aloft longer. Students with poorer balance tended to descend sooner and with more laughter. While smaller seeds might disperse farther, though, they would not have as much energy to germinate. Over the years, maple seeds have found a sweet spot within the larger range of variability that allows them to achieve sufficiency in both travel and growth.

Even with my nose still pressed up against the window, a hungry chickadee couldn’t resist swooping in for a fresh snack. Seeing my face startled it, though, and it backed up in a short hover before landing again. I smiled to see the shiny black eye so close to my brown ones, and admired the delicate detail of the feathers. Using a leading-edge vortex to generate lift isn’t just used by maple seeds (and similar samaras from ash, elm, and boxelder trees). Insects, bats, hummingbirds, and maybe even my chickadees all use this little bit of physics to help them hover, too.

What fun in just a little seed! As we all watch kids open oodles of expensive toys this holiday season, I can’t help but be grateful for the simple toys that nature provides. Nature’s toys aren’t free either, though. It’s just that they require our stewardship instead of our money. 

Sugar maple seeds. Photo by Steve Hurst @ USDA-NRCS PLANTS Database