Skull School

Skulls of every shape and size lined the Great Hall as the troop of scientists bumbled in out of the swirling snow. Each paused in awe as they realized what treasures awaited them. 

No, I’m not describing a scene from one the of the Indiana Jones movies. That’s how a group of Wisconsin Master Naturalists began a lesson on mammal skulls during our recent Wild about Winter Ecology Weekend. 

Cindy examines the flat face of a bobcat skull during a Mammalogy workshop. Photo by Emily Stone.

This is the third year I’ve hosted a three-day program at the historic Forest Lodge Estate on Lake Namakagon in late January. We’ve drilled holes in the lake ice to sample zooplankton, dissected bluegills to find developing eggs, followed porcupine tracks into a culvert, and learned the intricacies of how various critters survive the winter. This year, the focus was on mammals.

Dr. Julie Ray, who earned her PhD studying snakes in Panama, and who founded the Project Northwoods Nature Center in Winter, WI, brought her extensive skull collection to help us get a feel for the diversity of mammals in Wisconsin. Julie often shares these skulls, and her knowledge, with the high school students in Winter. 

I also share skulls with students, mostly as part of our MuseumMobile program that visits local schools. In the fall, I bring a tub full of skulls to the second grade classrooms, and we focus mostly on identifying herbivores, omnivores, and carnivores by their teeth. Herbivores have flat molars for grinding plants, and their front teeth might either be the sharp chisels of beavers and rabbits, or the bottom-only incisors of deer. Carnivores need sharp incisors, large canines, and serrated back teeth to help cut and tear their meat. Omnivores combine the flat molars with large canines so that they can eat a wide variety of foods. 

Recently, when I made my second MuseumMobile visit of the year, I quizzed the kids. “So, if the mystery animal I’m about to show you is a carnivore, what would its teeth look like?” “So, if the fake scat I’m about to show you is from an herbivore, what would its teeth look like?” Little hands shot into the air so enthusiastically that I thought a couple of them might fall out of their seats. Turns out that the skulls had made an impression during my first visit, and the students had no trouble remembering what they’d learned. 

Having never taken a Mammalogy class, though, I don’t actually know much more about the skulls than the basics I tell the kids. Julie began her lesson with some slides, and some ideas about how to infer an animal’s adaptations by the morphology of its skull. 

For example, the zygomatic arch—basically the animal’s cheekbone—helps to support the eye, and also helps you get a feel for how big the animal’s eyes are. I’ve studied the eye sockets of owls and been amazed at their size, but I hadn’t transferred this observation to mammals. For example, itty bitty pocket gopher skull in Julie’s collection had a relatively small zygomatic process, along with its sharp rodent teeth. 

Pocket gophers have small eyes. Photo by Emily Stone.

The location of the eyes is also important: predators have forward facing eyes for spotting prey, and prey animals have eyes on the sides of their head for a wider view of danger. 

While cute, floppy ears aren’t preserved on a skull, a small ear hole—also called the external auditory meatus—can be seen near the back of the jaw. You can get some idea of how important an animal’s hearing is by the relative size of the hole. I was impressed by the relatively large external auditory meatus on the bat skull! 

The external auditory meatus can be hard to find, but the foramen magnum (“great hole” in Latin) is much easier to see. This is the large hole where the spinal cord connects through to the brain. The orientation of this opening can help you figure out what posture the animal uses to walk. Except for humans, all the mammals in Wisconsin walk on all fours, so their foramen magnum is at the bottom and back of their skull. Humans’ is under the center of our skull, and chimps’ are in between. 

Have you ever compared the skull of a canid (dog family) to one of a felid (cat family)? Wild species of dogs and cats are some of our most well-known predators, and they eat many of the same prey, but their skulls look completely different. They both have the sharp, serrated teeth of carnivores, but wolves have a very elongated nose cavity, and cats have a pretty flat face. Why would that be? Canids use their sense of smell for hunting, and cats tend to sit and wait. Their adaptations and habits are indicated in their skulls. 

Julie passed out dichotomous keys—which allow you to compare two options at a time until you’ve identified what you’re looking at. Even she gets impatient with the long process, though, and gave this advice: “Just count the teeth! Opossums are the only mammals in Wisconsin with 50 teeth. If the skull has a lot of teeth, you’re done!” 

An opossum skull is easily identifiable by its many teeth. Photo by Emily Stone.

With this interesting lesson, and all of the skulls, there were a lot of smiles in the room, but I checked out her opossum skull, and sure enough, it showed me the toothiest grin of all. 

Best of all, we didn’t have to dodge poison darts or tiptoe through a room full of snakes to find our Great Hall full of skulls. Top that, Indiana Jones!

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new Curiosity Center kids’ exhibit and Pollinator Power annual exhibit are now open! Call us at 715-798-3890 or email emily@cablemuseum.org. 

Reading on the Beach

I slept with the sound of ocean waves crashing into the white sand beach. Through a full day board meeting in a cramped conference room, we kept an eye on swooping flocks of pelicans, took breaks on the balcony to inhale the smell of salt, and watched a thunderstorm toss dune grass into a frenzy. Everything from the humidity in January to the arc of wave-smoothed sand was outside of my normal realm. 

The palm trees mark the former end of the lodge where I was staying...pre-hurricane.

Mary Oliver, my favorite poet, lived on the tip of Cape Cod and often wrote about the ocean—a subject quite novel to me. Her poem “Breakage” begins, “I go down to the edge of the sea,” and goes on to name and describe the pieces of broken shells she finds on the beach. It ends, “First you figure out what each one means by itself…then you begin, slowly, to read the whole story.”

That concept I understand. I can go out in the Northwoods and read a story in the odds and ends of life I find there. But when I finally broke away from the group to take my camera for a walk on the beach in the late afternoon, the stories there seemed written in a foreign language. 

The strandline—where the last high tide had left its burdens—was a mosaic of colorful bits of shells. The jumble teased me with the hope that something there would look familiar; would be identifiable. Give me a similar assortment of torn leaves from bog plants and I could recognize every one, but the shells were merely pretty. 

Then I caught sight of one white shell with a tiny, perfect hole. Near it was another shell with a similar puncture, and another, and another. When I lived in northern California and took kids to the tidepools there, we’d found similar holes in the conical shells of limpets. The culprit: one of several types of snails. Snails use acid to soften the shell of their prey, and a hard-toothed tongue called a radula to drill a deadly hole. Using a combination of their radula and digestive enzymes, the snail turns the owner of the shell into soup, and slurps it up as a midnight snack. A quick Google search told me that moon snails are the most common malefactors on this beach.

Broken shells have stories to tell. Can you read them? Photo by Emily Stone.

The lovely remains of these grisly feasts are perfect for stringing on necklaces or adding to charm bracelets. 

In nature, beauty often cloaks a beast. 

The translucent blue balloons of Portuguese man o' wars are no exception. These were one of the first novelties to catch my eye on the beach, and I assumed they were jellyfish. Google soon set me straight. Despite its inflated top, trailing tentacles, and floppy translucence, The Portuguese man o' war is not a jellyfish at all. It’s a colonial organism. The balloon; the tentacles with their stinging cells; and all of its body parts are made up of different types of zooids that function together like a single animal and cannot survive independently.

Munro, C., Vue, Z., Behringer, R.R. et al. Morphology and development of the Portuguese man of war, Physalia physalis. Sci Rep 9, 15522 (2019) doi:10.1038/s41598-019-51842-1

Despite the Portuguese man o' wars famously fierce stings, once washed up on shore they are often eaten by ghost crabs. I was glad to happen upon this fact during my research, because it explains why many of the blue balloons I found were perched near the entrances of small tunnels in the sand. Those tunnels—as my Facebook friends informed me—belong to ghost crabs. 

A pretty blue Portuguese man o' war rests next to the entrance of a ghost crab’s hole. These jellyfish-like creatures pack a painful sting while alive or dead, but crabs are tough. Photo by Emily Stone. 

I’d been hoping that the tunnels were inhabited by Alabama beach mice, a species highlighted on a nearby interpretive sign. These endangered mice store the seeds of sea oats—and important sand-stabilizing dune grass—deep inside their tunnels. The sea oats seeds I found blowing around the beach looked dry and forlorn, while those forgotten inside the mouse tunnels find themselves in the perfect garden. Mice live farther up in the dunes, though, unlike the crabs who need to wet their gills in order to breathe. 

Sea oats play a major role in stabilizing sand dunes, and Alabama beach mice (not shown, a relative of our deer mice) both eat and plant their seeds. Photo by Emily Stone.

So, inspired by Mary Oliver, and assisted by my Facebook community and the internet, I’m learning a new tongue—one flavored by salt and full of the shushhhh of waves on sand. I’m beginning to piece together some of the stories on the beach. Snails drill holes in their neighbor’s shells, crabs eat colonial organisms that are not jellyfish, and mice plant seeds who stabilize the dunes. 

These characters seem even more exotic now that I’m back among dunes of snow instead of sand. But with all of her diversity, Nature has only so many plots in her literature. Wherever I go, I recognize the muffled drama of predation, the necessary work of scavengers, the magic synergy of cooperation, and the serendipity of accidental gardeners. Wherever we go, there are stories that we can learn to read. 

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new Curiosity Center kids’ exhibit and Pollinator Power annual exhibit are now open! Call us at 715-798-3890 or email emily@cablemuseum.org. 

Wild Turkeys

Snow crunched under my boots the other morning as I crossed the driveway to my car. A few dusky lavender clouds were just sailing away in the quiet dawn. Quiet only until a flock of wild turkeys exploded out of the nearby hemlock grove. Their big wings flapped and crashed through the branches as they spooked from the safety of their nocturnal roost. Three? Five? Six? of their big bodies zoomed over my head and vanished. Just a few minutes later, I chased a couple of these modern dinosaurs down the road in my car as they ran, searching wildly for the best route over the snowbanks. 

Turkey roosting near my house...

So I spent that morning researching turkeys. 

First, their explosive flight is remarkable. It’s easy to forget that these big, awkward birds can fly at all—until they suddenly flush up from the road or out of the trees. As you might remember from Thanksgiving dinner, turkeys have both white meat and dark meat. Those two types of muscles power different activities. Dark meat is well-oxygenated and therefore functions best during aerobic activities involving endurance—like walking, running, and scratching in the leaves for food. It’s no coincidence that if you like dark meat then you choose a turkey leg or thigh.

The white meat is made of fast-twitch fibers that excel at rapid, short-term activities, like bursting into flight and startling unsuspecting people or escaping a hungry bobcat. After all of that commotion, wild turkeys rarely fly more than about 100 yards. It makes sense, then, that white meat is on their breasts and wings. Birds who migrate long distances—like ducks and geese—have breast and wing muscles that are dark for endurance. 

Turkeys have excellent eyesight and great hearing, too, which is why it can be difficult to sneak up on them. Hunters still manage to find a way, though, and back in 1881, wild turkeys vanished from Wisconsin. It wasn’t just unregulated hunting that drove their decline. At that point, turkeys were only native to far southeast Wisconsin. Settlers quickly cut the oaks, which served both as nighttime roosts and food sources for the turkeys. Domestic poultry brought disease, too, which didn’t help. 

Photo by Larry Stone

A series of comically unsuccessful reintroduction efforts began as soon as 1887. Thousands of pen-raised birds and wild/domestic turkey hybrids were released by the state of Wisconsin between 1929 and the 1960s. These birds didn’t have the right instincts to survive predators and harsh winters. But it was difficult to catch the purely wild birds, so what do you do?

Turns out, you invent the technique of rocket netting. 

Have you heard of rocket netting? I hadn’t. But I mentioned it around the kitchen table that night with my new roommates. Ally and Laura are currently trapping small mammals in the Chequamegon-Nicolet National Forest, and staying at the Museum’s staff house for a few weeks, but these two wildlife researchers have worked on a wide variety of projects around the country. “Oh yeah,” said Laura, “I’ve used rocket nets to catch turkeys in Delaware.” 

Laura described the process of loading explosive charges into metal tubes and then attaching them to a big net. The rockets are mounted on posts. After that, you wire the system up to an electrical firing line, retreat to the blind, and wait until the turkeys come to a pile of bait. With luck, when you fire the rockets, they’ll carry the net over the birds and trap them. The technique was invented in the 1950s and quickly proved its usefulness. 

We found some videos of the rocket netting process on YouTube, and it looks like a booby trap from an Indiana Jones movie, with a thick net launching onto the flock, followed by much squawking and flapping. “They’re really pretty docile,” Laura continued. “They didn’t really peck or bite, but you did have to watch out for their spurs.” She pointed to a tiny scar still visible in the palm of her hand. Tom turkeys have a sharp claw, or spur, on the back of their ankles that’s useful for self-defense. 

With the use of rocket netting, wild turkeys from Missouri were caught and released in southwest Wisconsin in 1976. In return, Wisconsin gave Missouri three ruffed grouse per turkey. The 300-plus turkeys soon multiplied, and Wisconsin began an in-state trap and transfer program. Wild turkeys now occupy all 72 counties in Wisconsin—even up north where biologists originally thought that winters would be too harsh.

Photo by Larry Stone.

Turkeys are a wildlife conservation success story. Sometimes too successful, like when turkeys move into residential areas and become pests. It helps that they eat just about anything related to seeds or insects. Sightings seem high this year, with plenty of acorns for them to forage on. They’ve also been spotted eating frozen crab apples while awkwardly perched in tiny trees. And even when deep, fluffy snow causes some turkeys to starve to death, their numbers can bounce back in a single breeding season. 

With explosive flight, explosive nets, and explosive populations, these common birds are pretty entertaining to have bursting out of my hemlock grove.

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new Curiosity Center kids’ exhibit and Pollinator Power annual exhibit are now open! Call us at 715-798-3890 or email emily@cablemuseum.org. 

A Hike with Auntie Em

2020: Zac checks out the fort from the inside.

Christmas at home with my niece and nephews was wonderful as always, but now that the twins are 10, it’s not quite like it used to be. Sure, we spent a few hours leaning big sticks up against in a tree in a sort of teepee fort, and Kylee is still small enough for piggy back rides, but I miss the old days. I thought you all might like to reminisce with me. So here’s an account of Christmas break in 2016 when they were enthusiastic six-year-olds!

2020: Zac adds prairie grass to the fort for insulation.

2020: Kylee and I took a "girls only" hike to the top of the next hill.

2016:

“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?

Zac and Kylee maneuver a stick together. 

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. 

Zac and Kylee poke at puffball mushrooms.

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!

A special thanks to my big brother for having such great kids!

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new Curiosity Center kids’ exhibit and Pollinator Power annual exhibit are now open! Call us at 715-798-3890 or email emily@cablemuseum.org. 

What Opossums Eat and Other Interesting Facts

“Roadrunner! Tofu muffin! Bala shark!” “Hey, look, two opossums!”

Family game time over Christmas break had us shouting some odd combinations of words around the dining room table. While most were guesses for a variation on charades that we call Salad Bowl, the opossums were seen drinking from my parents’ water feature and cleaning up fallen seeds under the bird feeder. It took my 15-year-old nephew several minutes to help me spot their long, white faces peeking through the dark prairie grass. 

Photo by Cody Pope, Creative Commons.

They may not be as cuddly as koalas, but North America’s only marsupials are surprisingly cute.

A couple of decades ago, during a bitterly cold winter in northeast Iowa, I remember cringing at the sight of a sad opossum with a black, shriveled, frostbitten tail. I felt sympathy and disgust at the same time. Since temperatures barely fell below freezing over this holiday season, these critters were looking significantly happier. That seems to be a trend. 

And you know, I’ve become more excited to see them, too. In recent years, scientists have calculated that opossums will eat up to 5,000 ticks per season. Since ticks carry Lyme disease, babesiosis, ehrlichiosis, anaplasmosis, and several other nasty ailments, having plenty of little tick-Hoovers in our native prairie seems like a great idea. 

The key is that opossums are fastidious groomers, and whenever they find a tick, they lick it off and swallow it. This takes care of more than 90% of the ticks that attempt to draw their blood meal from an opossum. According to one forest ecologist, opossums are net destroyers of ticks. In comparison, mice are super lazy about grooming and are some of the primary carriers of Lyme disease and feeders of ticks. 

Hardly a summer goes by where my parents don’t take at least one course of antibiotics for Lyme or another tick-borne disease. Without opossums moving into our woods, it could be worse.

And it truly is moving in. The pre-settlement range of Virginia opossums (their official name) was focused on the South. They only went as far north as southern Illinois and Missouri, and didn’t extend all the way east or west. Since 1900, and especially in the past 20 years, opossums have moved all the way up the Atlantic coast to Maine, north to Canada, and west to Colorado. 

Geographic range expansion of the Virginia opossum (Didelphis virginiana) since 1900. The historical range (circa 1900) is shown in light gray and the present range is shown in dark gray. The black star represents the study area. Ranges modified from Gardner and Sunquist (2003) and Reid (2006). 
Source.

Originally, it was the clearing of dense forests that facilitated their northward march. Currently, warmer winters seem to be the key factor in their expanding range, and their occurrence seems to be restricted by temperature and snow depth. Opossums now inhabit all of Iowa and Wisconsin, and most of Minnesota. They were even introduced to the west coast as a food source during the Great Depression. (Recipes containing opossum can be found in early editions of The Joy of Cooking!)   

Like cardinals who have followed bird feeders northward, opossums seem to have followed trash cans. At the northern edge of their range, they’re better able to find food and shelter around human habitation. 

From warm beginnings in South America—waddling beneath the dinosaurs—opossums traipsed northward across the newly-formed Isthmus of Panama to North America, two million years ago. In order to spread even farther north, opossums have had to adapt. 

In ecology, there are three “rules” that describe how animals vary from the southern reaches of their range to their northern limits. Bergman’s Rule states that animals will have larger body sizes in colder climates. Larger bodies store more fuel for the hungry days of winter, and they lose less heat. Allen’s Rule talks about the benefits of shorter extremities when staying warm is a struggle. Shorter ears, for instance, are easier to keep from freezing. Gloger’s Rule describes the trend of less pigmentation at northern latitudes. 

These rules apply to mammals, but not many scientists have looked at them in relation to marsupial mammals. As it turns out, opossums fit the patterns nicely. Northern opossums have bigger bodies, shorter ears and tails, and thicker fur. You can easily imagine how those traits are advantageous in cold places. 

Northern opossums also have paler skin. The brown melanins in skin contribute to the immune system’s ability to ward off bacteria and fungi, which are more common in warm, wet climates. Up north, pathogens are less common, and the pigments are less necessary. 

One of opossums’ greatest advantages for expanding into new areas is simply their un-picky eating habits. They’ll eat trash, grubs, cockroaches, rats, mice, slugs, dead stuff, rotting fruit, and even venomous snakes. Opossums’ opportunistic diet couldn’t be more different than the beef-stick-and-cookie cuisine that the younger members of our family seem to thrive on. But the variety is similar to the random words entered in our Salad Bowl game. Roadrunner, tofu muffin, bala shark…I bet an opossum would eat them all!

Emily’s second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. 

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new Curiosity Center kids’ exhibit and Pollinator Power annual exhibit are now open! Call us at 715-798-3890 or email emily@cablemuseum.org.