A Slow Moving Symbiosis

On our first morning in Costa Rica, my group of 14 Museum members on the Natural Connections in Costa Rica trip rode through San Jose, over hills, and past volcanoes. Soon we left the Central Valley and headed for the Caribbean coast on our way toward breakfast. When—at last—the gates opened and we pulled into El Ceibo restaurant near Guapiles, Jimmy (our local guide) conferred with the gate operator briefly, then turned to us with the news: “There’s a sloth in the tree across the road!”

You can see that this sloth has three "fingers" as well as three toes. Photo by Emily Stone.

Naturally, we all piled off the bus with binoculars and cameras in hand. The two-toed sloth was just a fuzzy brown ball. Both two-toed and three-toed sloths live in Costa Rica. They all have three toes—but they have different numbers of fingers. Some scientists have started calling them by the more accurate name, “two-fingered sloth,” but to me that just sounds like a whiskey drink.

After everyone took a turn looking through Jimmy’s spotting scope, we headed inside for a breakfast buffet of beans, eggs, salsa, sausage, fried plantains, fresh fruit, and more coffee. It was a very different meal than what the sloth was eating. The sloth would also have to chew its purely leafy entrée twice: first on the way in, and again after the meal was fermented in a foregut.

Two- and three-toed sloths are both members of the elite club of arboreal (tree-dwelling) herbivores (solely eating plants), but they aren’t closely related. According to a 2014 article about sloths in the Proceedings of the Royal Society, by University of Wisconsin-Madison professor Jon Pauli, “only 10 species of mammals are considered specialized arboreal herbivores.” That’s just 0.2% of ALL mammal species!  There’s a reason that cows don’t climb trees. The large stomachs required to digest their grassy diet are better suited to firm ground. Squirrels, on the other hand, focus on energy-dense nuts and seeds, and therefore don’t need a big gut to fuel their frenetic metabolism.

All of the world’s arboreal herbivores (including sloths, koalas and some monkeys and lemurs), have converged on a few common traits. First, they all weigh between 2 and 31 pounds. This size range reflects the tension between being small enough to climb, while still having a big enough stomach to digest tough plants. Their adaptations include ruminant-like digestive organs, slow metabolisms, and unusual behaviors.

For instance, sloths have taken a page from the reptiles’ book, and they sunbathe to help regulate body temperature. They also sleep a lot. Wild sloths sleep around 10 hours per day. Sloths in captivity give the others a bad name by sleeping up to 20 hours per day. I felt lucky, then, when we wandered outside after breakfast and caught a glimpse of a different two-toed sloth climbing across a branch with her baby. Two-toed sloths eat a somewhat more varied diet, and move greater distances.

A two-toed sloth (who still has three toes on her hind feet) and her baby climbed across this limb while we watched. Photo by Carol Werner.

On the other side of the parking area, a single three-toed sloth blended perfectly with a lichen-covered tree trunk. It was moving just fast enough for us to get a feel for their characteristically graceful and deliberate movements. Also, its permanent “Mona Lisa smile” was adorable.

This three-toed sloth has a "Mona Lisa smile." 

While at first glance sloths may not appear to be the epitome of adaptation, they are actually an amazing, (slowly) moving hub of symbiotic partnerships, which Jon Pauli—from Wisconsin!—helped elucidate. It all begins when the sloth climbs down for its weekly bowel movement (sloths have the slowest known digestion rate of any mammal). During this trip to the soil, the sloth picks up fungal spores from a species that lives on its fur and helps ward off parasites. In addition, moths emerge from the sloth’s fur and lay eggs in the sloth’s droppings. The moth larvae feed off the dung, and then fly back up to the sloth after metamorphosis. This tight relationship seems to be part of the reason that three-toed sloths stick to living in just a few neighboring trees.

The adult moths seem to feed on secretions from the sloth’s skin, as well as algae on the sloth’s fur. Moth droppings act as a fertilizer, while grooves on the sloth’s fur create a little hydroponic irrigation system for the algae. Neither the algae nor the moth species occur anywhere but on a sloth (or on its dung).

While Pauli hasn’t yet calculated exactly how much energy sloths obtain from eating algae off their own fur as the groom, he has determined that the algae are a better source of fats than the tree leaves in the sloths’ diet. Keep in mind: a three-toed sloth only burns about 110 calories per day. The value of the moths and algae must be significant, because climbing down to defecate costs the sloth 8% of its daily energy budget, and puts it at high risk of predation.

We were happy to simply watch the sloths as they went about their slow business of living. Just looking at their thick fur coats made me uncomfortable as the temperature rose; but their languid movements were a good reminder of what it means to relax on a tropical vacation.

Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/.  Listen to the podcast at www.cablemusum.org!

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!

Neotropical Migrants

Pineapple juice dripped down my chin. Sweat ran between my shoulder blades. And this was just at breakfast. The dining room at Selva Verde Lodge in the Sarapiquí region of north-central Costa Rica was bright and airy, with ceiling fans and open windows. It was still 85 degrees and humid. This beautiful lodge is situated on 500 acres of tropical forest that was rescued from logging in 1982, by Giovanna Holbrook, a visionary conservationist whose story reminded us of the Cable Natural History Museum’s founder, Mary Griggs Burke. Ms. Holbrook also created Holbrook Travel, the company that expertly arranged our trip.

Selva Verde Lodge is the home-base of Holbrook Travel in Costa Rica.
Mrs. Holbrook protected it's 500 acres and began building facilities in 1982. 
Yes, that is a Christmas tree in the back right corner. It felt a little out of place to us...

By now, our Natural Connections in Costa Rica trip was about halfway into our nine-day adventure, and we knew the drill well. The breakfast buffet, which started with a pyramid of fresh pineapple, watermelon, and papaya, also contained generous portions of gallo pinto, scrambled eggs, odd-looking sausages, and fresh cheese. A different flavor of fresh fruit juice flowed like water each morning, and rich, dark, coffee filled our cups.

We were all comfortably dressed in shorts and sandals, with little need to worry about hauling around extra warm layers. Sun protection was our biggest concern, but thick leaves and shade structures abounded. Binoculars and cameras hung around our necks.

Birding in the jungle.

When I thought of home, I imagined the bare trees, freezing temperatures, absence of mosquitoes and ticks, and my larder full of blanched kale. Not bad, just different.

After joining the clean plate club, I went out on the deck of the dining room to have a peek at the bird feeders. A wooden platform held bananas the way we’d spread out corn up north. It was also covered with jewels. Vibrant green honeycreepers and shining honeycreepers fluttered almost like hummingbirds as they jockeyed for position. Passerini’s tanagers wore tuxedos of the blackest black with shimmering red sashes. The cloud of drably named blue-gray tanagers could have plucked their hues straight from the sky. Our chatter from behind our binocs included adjectives like “ridiculous!” “crazy!” “so bright!” and “it glows!”

Green Honeycreeper Female

Green Honeycreeper Male

Shining Honeycreeper Male

Shining Honeycreeper Female

Passerini's Tanager Male

When a striking black and orange bird swooped in for his turn, his colors fit right in, but I still did a double take. Instead of a strange new surprise, this was an old friend. Baltimore orioles are connoisseurs of ripe fruit, and can be lured into northern bird feeders with oranges and grape jelly. Since sunflower seeds and suet just won’t cut it for orioles, these neotropical migrants make an incredible journey to Central and South America for the winter.

Baltimore Oriole Male

 

We made that migration, too. Despite being ensconced in a jet plane, the flight from Minneapolis to Miami to San Jose was less than pleasant. Even if we hadn’t hit the worst turbulence of our lives in a Georgia thunderstorm, the plane was cramped and stuffy, and the security lines long. It’s amazing that such small birds can survive the journey. At least they get to stretch their legs and breathe fresh air!

The reality is, though, that many birds don’t survive migration. One study published by the British Ecological Society calculated that birds’ mortality rate is six times higher during migration than in their summer or winter habitat. Although these two perilous periods are relatively short, migration accounts for more than half of annual mortality.

So why risk it?

Well, staying in a northern winter isn’t much safer. Golden crowned kinglets are fantastically adapted winter residents of some of our coldest climates. Even so, part of their adaptation includes a higher than average reproduction rate in the summer to compensate for expected mortality in the winter.

Besides that, if you’re adapted to eating fruit or insects, or frogs you don’t have many options. Many of us can relate to the desire to follow “summer” year-round, with its associated warmth, sunshine, and fresh food.

The fruit was so enticing, in fact, that I went up for seconds. Now both the orioles and I had watermelon juice dripping down our chins. What a wonderful life it is for us neotropical migrants who survive the trip!

The full feeder at Selva Verde Lodge. photo by Emily Stone.

Special Note: Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/.  Listen to the podcast at www.cablemusum.org!

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!

Summer Blooms with Lois Nestel

Well, by the time you read this I will have returned from a nine-day trip in Costa Rica with a group of Museum members. While I’m off gallivanting in a tropical rainforest, I thought I’d give my readers a short break from the winter weather, too. Please enjoy this little taste of summer from June 2017. I’ll have more tropical reports when I return!

***

On a recent mountain bike ride with a group of women, I quickly fell behind the lead group while easily staying far ahead of the beginner group. Alone in the forest on the first hot day, it was bliss. The Makwa Trail flowed gracefully through deciduous woods south of Seeley, WI, and as evening fell, I wallowed in the rich smells of the summer woods.

Riding alone allowed me to stop and smell the roses. The bright white flowers of wild strawberries and the canary yellow flowers of barren strawberry (both in the Rose Family) lined the trail. The first produces a juicy red berry, the second, despite its similar set of three toothy leaves and five-petaled flowers, only makes a few dry seeds. Trilliums, violets, starflowers, bluebead lily, and a late-blooming wood anemone also caught my eye.

I’m pretty sure that Lois Nestel, the Museum’s first naturalist and director, would never have joined me on a mountain bike ride, but I know I would have loved walking attentively through the woods with her. This week, I’d like to share her description of the residents of woods and fields as summer begins to bloom. Slow down a minute with me, we’ll smell the roses, and I think you’ll find it rewarding.

Calopogon tuberosus, grass-pink orchid in a bog. (With a crab spider!)

Lois wrote, “Although the woodland flowers of spring are passing as increased foliage cuts off the light, there are still numbers of delightful varieties to be found. Both pink and yellow lady-slippers are blooming now as are some of the bog orchids. Many smaller shade-loving blooms may also be found if one cares to expend the extra energy to find them. Dainty gold-thread, pipsissewa, and twinflowers lift their lovely blooms only two or three inches above the forest duff. The dwarf dogwood, known as bunchberry, masses its four-petaled green and ivory flowers along banks and around old stumps, and nearby the yellow bloom of Clintonia or bluebead lily may be found.

Bunchberry

“But from now until autumn the floral emphasis will be upon the blossoms of open areas, roadsides, fields and glades—and the variety seems endless. Drifts of color along roadsides and in meadows are more spectacular than are the more modest flowers of spring. Daisies, hawk-weed, and other composites now dominate the scene, and the yellow-flowered salsify, best known in late summer for its huge dandelion-like seed head (commonly known as goat’s beard), is one of the most interesting. It is related to the oyster plant grown in gardens.

“Perhaps the loveliest flower of the season is the wild rose, and differences in varieties and habitat allow their season to be quite extended. While color may vary from deep pink to almost white, the typical rose fragrance varies little. Simple perfection personifies the rose.

“In damp meadows, golden alexanders spread their wheels and along the edges, in sheltered nooks, wild columbine nods its spurred bells. In drier fields and roadsides, flat-topped aromatic heads of yarrow vary from dingy white to mauve or pink. From hillside to hallow, from northern to southern exposure, great differences can be seen in the development of the floral community. In sunny, open areas some plants will already be seeding while their counterparts in cool depressions are only in bud.

“Summer’s profusion together with our modern way of life can be a disadvantage. Traveling swiftly by car, one sees sheets and belts and blurs of color…sees and yet does not see. The quantity bedazzles, the quality is not seen.

“Take time to walk, to examine the intricacies of the individual flower; look for the less obvious. It is rewarding.”

Special Note: Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/.  Listen to the podcast at www.cablemusum.org!

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!

Big Tracks and Cold Toes

As usual, my toes were cold. So, I hopped off my fat bike and began jogging down the trail beside it instead, trying to wiggle warmth back into my feet. Crunch, crunch, crunch, I ground icy snow under my boots with every step. The day before had been well above freezing, and the briefly slushy snow was now even more solid.

I was keeping an eye on the edge of the trail when my foot landed next to the track of a larger foot. This wasn’t just some deer hunter’s big snow boot. This wide track showed five toes. And claws.

I know this is supposed to be a photo of a bear track, but I also thought I should explain that my mom added those sweet blaze-orange cuffs to wind pants I got from a thrift store while at Northland College. They provide excellent visibility whether I'm biking or running! 

Black bear!

I looked into the woods behind the track. Then I glanced across to the other side of the trail. More tracks scuffed the snow and headed down a steep bank toward a wetland. My urge to follow the tracks was strong, but these were big tracks. Somewhere at the end of the trail was a big bear. I examined them more closely. The bottom of each track was compressed and translucent—obviously made in the previous day’s slush. A sprinkling of snow pellets filled the depressions made by heel, ball, toes, and claws. These tracks were at least 24 hours old.

Cautiously I pushed through twiggy balsam firs and followed the trail downhill. Big, punchy tracks continued across the hummocks of the still-damp marsh. Not wanting to get my already cold feet wet, I turned back.

Besides “how close is he?” the main question on my mind was, “why was he still awake?” Bears should be hibernating right now, shouldn’t they?

Scientists think that hibernation is usually triggered by a combination of weather and lack of food. For example, 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.

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. A den’s small opening, snug fit, and a layer of duff on the floor also help them retain heat, although solo bears are commonly found hibernating in relatively unprotected places as well. Mother bears, on the other hand, are much more likely to stay put in snug dens while their cubs are born.

The definition of hibernation itself has been evolving over the years as scientists learn more about the winter physiology of bears and other hibernators. While it used to focus on animals who 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.

What happens, though, when there is shallow snow and plenty of food? After I mentioned those big tracks to a couple of biologists, they shared their own recent bear-track-sightings, and hypothesized about the cause.

First, adult male bears use shallower dens, or even den above ground. This makes them more prone to disturbance, especially with the light snow cover and some mild days. Deer hunters may have awakened the bears. In addition, both bait piles of corn and gut piles from harvested deer may have been providing bears with a source of food that convinced them to stay awake.

Two very recent scientific studies support those hypotheses. In Russia, researchers found that when warmer temperatures occurred near their brown bears’ typical den entry and den exit dates, the length of their hibernation was shortened. The scientists are worried that this might make it harder for the bears to cope with climate change.

Closer to home, near Durango, Colorado, researchers found that both warmer temperatures and increased food availability impact the timing of when black bears enter and exit their dens. One downside is that this lengthens the bears’ active period—and increases the portion of the year when they could come into conflict with humans.

That’s a concern I share. I eagerly await the first good snow so that I can safely hang my bird feeders. I’m also not used to being bear-aware during my winter activities. As fun as it was to see those tracks, I’m very glad that they weren’t fresh. As I hopped back on my fat bike for the slog home, I just had to wonder—were his toes cold, too?

Lynch Creek Wildlife Area, Chequamegon-Nicolet National Forest

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Emily was in Alaska for the summer. Follow the journey in this column, and see additional stories and photos on her blog: http://cablemuseum.org/connect/.

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!” is open.