A Stomach for the Holidays

While digesting one of the many rounds of holiday feasts and leftovers, with plates of cookies in between, a headline caught my eye: “Big brains or big guts: Choose one.”

As much as the post-holiday-dinner-brain-fog is real, I don’t love the implications of those options.

Luckily, the article wasn’t about humans. It was examining birds in cold, highly variable habitats, and their struggle to survive. Essentially, birds have two options: spend energy maintaining a big brain that allows them to find high-quality food, or spend energy maintaining a large stomach that can make low-quality food sufficient in high quantities. According to the research, if you are a bird who needs to survive cold winters, you must choose one. There’s no middle ground.

Last week I wrote about ruffed grouse feeding on the berries, buds, and twigs of mountain-ash trees. Grouse are the poster children for the success of birds with large stomachs and small brains. Even as ruffed grouse fly into windows, dart out into the road, and strut through my campsite unaware, I’ve tried to defend their intelligence. They are successful as a species after all, but that’s due to an evolutionary-level intelligence rather than individual intellect.

A ruffed grouse sits and digests the contents of their large stomach in a protected place. 

Photo by Kevin Friedman.

The benefit to having a small brain is that grouse put their energy into having a large stomach—and growing it even bigger for the winter. Back in the 1960s, two biologists “sampled” spruce grouse in Alberta, CAN, every month for a year. (I hope that they ate those poor, dissected grouse for dinner and didn’t let them go to waste.) Pendergast and Boag found that the grouse’s gizzards grew by 75% in winter, and the rest of their digestive tract increased in length by 40%.

The scientists hypothesized that when grouse switch from summer berries and insects to winter conifer needles (for the spruce grouse) and buds, twigs, and catkins (for the ruffed grouse) their gizzards must expand to hold more food and get strong to grind tougher food. Captive birds kept as controls and fed nice, digestible food didn’t exhibit any seasonal change in their digestive systems. Another study showed that stomach size decreases as grouse and ptarmigan diets became more digestible, so needle-eating spruce grouse are at the large end of the stomach spectrum among their cousins. That their brain is at the small end is evidenced by spruce grouse’s nickname “fool hen.”

Having a robust digestive system is made even more important because grouse aren’t good at storing fat. They must eat a lot every day to fuel their metabolism and get through winter. But while they are feeding—often in the tops of aspen trees—they are exposed to cold, wind, and predators. Their solution is to eat fast and save digestion for later.

While exposed, grouse feed quickly, packing 10 percent of their bodyweight in food into a pouch in their esophagus called a crop. Then they hide away in a dense thicket, or dive into a snow roost, to digest in peace and safety. This strategy doesn’t keep every grouse alive, but come spring, the survivors have lots of babies who need little parental care, and the population will rebound.

Other animals who have similar diets to grouse also grow bigger stomachs in the winter to accommodate fibrous food. Voles, for example, show a winter increase in the mass of their gastrointestinal tract, and especially the cecum. The cecum is a pouch in between the large and small intestines where microbes ferment fiber and make nutrients available to the vole.

The stomachs of white-tailed deer also expand in the winter to accommodate a larger quantity of lower quality food. And deer, with their four stomachs, have a much more elaborate system of microbial fermentation than the voles. The catch is that their microbes adapt to seasonal changes in their diet, and feeding deer corn or other supplements in the winter can kill them through rumen acidosis.

Of course, not all animals grow bigger stomachs in the winter. Shrews shrink their entire body, even their skull, by about 20 percent so that their metabolism can keep running at full tilt but survive on less fuel. Fish, like pumpkinseeds, who become dormant in the cold winter water, save energy by shrinking their gut until right before spring spawning.

And then there are the birds at the opposite end of the spectrum from grouse: black-capped chickadees. Their brains, not their stomachs, get bigger in winter. Let that information digest, and I’ll tell you more next week.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

The Color Splash of Mountain-ash

In a landscape of winter white, bits of color really pop. Recently I was on the North Shore of Minnesota when they received several inches of fluffy, wonderful snow. Gray clouds hung low and continued to sprinkle fairy dust throughout the following day. Out on the cross-country ski trails above Grand Marais, my yellow jacket shone against the snow. When a strip of blue sky finally peeked through the clouds, that, too, glowed brightly. Full sun would have been blinding!

Spots of red also caught my eye. The forest seemed decked out for Christmas with clusters of mountain-ash berries adding color in the woods along the ski trails, around town, and on the rocky shore of Lake Superior. One section of scrubby forest between Highway 61 and the lake seemed to be almost entirely composed of berry-laden mountain-ash trees.

As the days grow ever shorter and darker this time of year, splashes of color like these berries do wonders for my mental health. Ruffed grouse appreciate them even more, I’m sure, as they perch in the dark purple twigs and nibble both berries and buds. The berries are acidic enough to last on the tree all winter, but if a flock of cedar waxwings descends, all the fruits may disappear in a single day. Thrushes, jays, catbirds, and grosbeaks, plus squirrels and small mammals, sometimes share in the feast.

Mountain-ash berries brighten up the winter woods, especially along the North Shore of Lake Superior. Photo by Kevin Friedman.

Grouse eating mountain-ash berries. Photo by Kevin Friedman.

The twigs of mountain-ash apparently are tasty, too, or at least nutritious. When I taught a wolf ecology course on the North Shore years ago, we observed the impacts of deer browse in different parts of wolf territories. Any mountain-ash short enough for deer to reach was deformed from their nibbling. On Isle Royale, scientists observed that over eighty percent of mountain-ash stems in study plots were browsed by moose. Moose have the advantage of height. Snowshoe hares must browse the lowest twigs with their sharp incisors, or wait for deep snow to give them a lift.

Photo by Emily Stone.

Back in the day, when I took a plant identification course at Northland College, we only learned two species—American mountain-ash (a native) and European mountain-ash (Sorbus aucuparia, introduced for landscaping). So, for years, when I’ve found these trees away from towns, I’ve called them all Sorbus americana. Recently, I’ve discovered that showy mountain-ash, Sorbus decora, is also native here, and is more common, at least in Wisconsin.

The three species are almost identical to the casual observer. While the leaves are slightly different sizes and shapes, this time of year the hairiness of the buds and berry stems seems to be the best distinguishing characteristic. The buds of the European species will be covered with long, white hairs. Showy mountain-ash twigs and buds are pubescent (with short hairs) and American mountain-ash twigs and buds are usually smooth and hairless.

I always thought this tree was a European Mountain-ash. Now I'm not so sure--but it's been cut down so I can't go back and look closer! Photo by Emily Stone.

All of these species are good wildlife and landscaping trees, although planting the native mountain-ashes is preferred, since the European ones have been known to escape into the wild. While their showy, rounded clusters of white flowers don’t look like roses from afar, they are all part of the Rose Family. A closer look at the flowers reveals five white petals very similar to the blossoms on their cousins: strawberries, raspberries, cherries, and apples. Even the fruits of mountain-ash look like mini apples.

I took this photo of mountain-ash flowers on Hunger Mountain in Vermont during graduate school. From the leave length-to-width ration I measured off the photo, this is Sorbus decorum. Photo by Emily Stone.

Mountain-ash drupes that look like mini apples. Photo by Kevin Friedman. 

The hyphen in their name indicates that they aren’t really related to ash trees. Mountain-ash are called that because they have compound leaves with long, narrow leaflets, similar to true ash trees. Unlike true ash trees, these wonderful wildlife trees won’t be impacted by the deadly emerald ash borer insects.

Ash-like leaves on a mountain-ash. Photo by Emily Stone.

Both of our native species reach their southwestern edge in northern Wisconsin and Minnesota, and extend north and east from there. American mountain-ash also extends down the spine of the Appalachians. The happiest specimens seem to be concentrated along the north shores of Lake Superior and Lake Huron. They are quite common among the balsam fir trees on Isle Royale as well. On the water-limited bedrock along Artist’s Point in Grand Marais, I’ve noticed they can remain quite shrubby, and a heat wave last summer left their leaves brown and crispy.

The color these wonderful berries bring to our winter woods is only one reason I enjoy them. Getting to watch and listen to the flocks of birds they attract is another. And now, the challenge of learning to distinguish the two native species will give me an excuse to look more closely at their leaves and twigs. In doing that, I bet I’ll learn something else new, too.

Cedar waxwing in a tree that I once thought was European mountain-ash, and now can't be sure. Photo by Emily Stone. 

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Red-eyed Vireo Nests: Hidden Treasures of See-Through Season

Cold air filled my lungs as I climbed yet another flight of stairs up to the observation tower at Copper Falls State Park. It was interesting looking out through the twigs and trunks. The lack of leaves in this “see-through season” reveals aspects of the landscape otherwise obscured. For example, “Check out that nest!” I exclaimed to my friend, and we admired the small cup suspended between a Y in the sugar maple twigs. It was a lovely reminder of a favorite summer resident, now gone for the winter.

Can you see through the forest and spot the vireo nest? It's fun to get to look down on one! Photo by Emily Stone.

The placement of the nest dangling below the forked twigs, plus the few pale strips of paper from a bald-faced hornet nest woven among grass, bark, and pine needles, told me that it was likely built by a red-eyed vireo. While red-eyed vireos are one of the most common birds of eastern and central North America, these small, olive-green songbirds are hard to see among the leaves in the dense forests they prefer. Once the leaves fall, though, their nests are suddenly one of the most visible and recognizable of any songbird.

It's the female vireo who builds the nest in spring. She usually chooses a deciduous tree or shrub and places the nest 10-15 feet above the ground, and far enough out from the trunk so that it doesn’t block their view. Suspending a nest near the tips of thin branches reduces access for heavy nest predators like squirrels. On the chosen branch, the vireo weaves together fibrous strips of the inner bark of trees and other plant fibers to suspend the nest between the twigs. Pine needles often line the 2-inch-diameter inner cup. Spider webs help stick it all together.

As mentioned above, vireos often decorate the outside of their masterpiece with paper strips stolen from last season’s abandoned bald-faced hornet nests, even when those nests are not found nearby. Naturalists suspect that décor can trick potential predators into thinking it’s the nest of a furious stinger instead of a tasty songbird. Strips of birch bark often add to the papery look.

Almost every bird nest is a work of art. They are also feats of engineering that gently cup fragile eggs and chicks while withstanding storms, and then remain intact long past their intended use. Plus, they were constructed without opposable thumbs!

There’s a display at the Cable Natural History Museum that reinforces my awe. A Museum naturalist, decades ago, deconstructed a red-eyed vireo nest and catalogued each component. The nest included: 1 cherry stem, 1 piece of paper, 1 ball of tree sap, 2 pieces of thread, 7 fir needles, 9 plant buds, 69 pine needle sheaths, 16 pieces of hornet nest, 24 twigs, 50 animal hairs, 346 pieces of birch bark, 347 pine needles, 427 pieces of inner bark, and 16 pieces of spider web. The naturalist arranged these objects, minus the spider webs, in a beautiful display that hangs in our classroom.

This deconstructed vireo nest is a favorite display at the Cable Natural History Museum. The number of different nest materials is astounding! Photo by Emily Stone.

Despite the birds’ hard work, and the hornet paper, red-eyed vireo nests are vulnerable to nest parasitism by brown-headed cowbirds. When vireos can place their nests in the heart of a forest this is less common, but any vireo nest near a forest edge may end up with a cowbird egg among the 3-4 vireo eggs. The cowbird hatches first, grows faster and bigger, and will often push their adopted siblings out of the nest. Occasionally vireos will cover up the cowbird eggs and try again, but more often the parents just feed the big baby as one of their own. Vireos may nest multiple times per summer, especially if early nests fail.

Recently I noticed two vireo nests in the tops of trees surrounding my own driveway. Although the nests are much higher than average for a red-eyed vireo, that was the only vireo species I heard singing last summer. Warbling vireos are known to nest up high, but I would have recognized their run-on song, which sounds like them saying, as if to a caterpillar, “when I see you, I will squeeze you, and I’ll squeeze you ‘til you squirt!” Instead, I heard red-eyed vireos singing the incessant phrases “hear I am, over here, in a tree, look at me, vireo!”

All summer, it’s much easier to hear red-eyed vireos singing than to actually see one high in the treetops. This signing male was a lucky find! Photo by Emily Stone.

As their abandoned nests fill with white snow instead of white eggs, the vireos themselves are filling up on fruit in the Amazon basin of South America. When they return next spring, the females will start building new nests. Once the leaves fall, we’ll have a whole new set of treasures to discover in “see-through season.”

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Winter Songs of White-Throated Sparrows

During a recent week-long visit to the Washington D.C. area, finding pockets of nature with plenty of birds was a boon to our sanity. Early in the week, my partner and I drove west to the little town of Linden, Virginia, which provided the nearest access to the Appalachian Trail. Even as we crossed the gravel parking lot toward the oak-filled forest and uphill climb, a wistful-sounding white-throated sparrow sang from the brush. We looked at each other and grinned.

The rhythmic whistle of white-throated sparrows is part of the spring and summer soundtrack of the Northwoods. No hike or paddle is complete without their song. Two decades ago, while my parents helped me pack for a May trip to the Boundary Waters, this was the one song they’d insisted I learn to recognize. Luckily, it wasn’t hard. The white-throat’s pattern of two long starter notes followed by three sets of triplets is often described with the mnemonic “Oh, sweet Canada, Canada, Canada” and is quite distinctive.

But it’s been a month or more since we heard the last sparrow sing goodbye to the Northwoods as they headed south. I felt a little sheepish, realizing I’d never paid much attention to where they were going. Virginia, as it turns out, is in the core of their winter range. As we hiked, it seemed like almost every scritching sound in the underbrush turned out to be a foraging sparrow using their two-footed hops to unearth seeds in the duff. Getting a glimpse of snazzy black-and-white head stripes, yellow near the eyes, and the signature white throat patch confirmed their identity.

White-throated Sparrow. Photo by Larry Stone. 

Higher up in the trees, cardinals whistled, tufted titmice peter-peter-petered, Carolina wrens chattered energetically, and Carolina chickadees scolded each other. These are common winter compatriots of the white-throated sparrows.

A few days later, we crossed over a babbling brook on a wide wooden bridge and into the “R. Randolph Buckley ‘8-Acre’ Park” in Clifton, Virginia. Large beech trees, sycamores, oaks, maples, and pines, plus musclewood and a blooming witch hazel, welcomed us into this little neighborhood woodland. As we followed our ears to a white-breasted nuthatch high in a pine tree, a song burst out of a bush beside us. The white-throated sparrow riffed on the usual song, experimenting with a gravely “sweet can-a-NA-da can-a!” “Jazzy!” We laughed to each other. Listen here!

I don’t usually expect birds to sing in their winter habitat. Birds’ songs are typically used to attract mates and defend territories, and therefore are most useful in spring and summer. Many birds get by using simple call notes to communicate within a flock over the winter. So, we figured we were hearing young males practicing for the coming year. That would also explain why the amateurs’ “sub-songs” were tending shorter and with more variations in rhythm and tone. As it turns out, that was only part of the story.

Singing on their wintering grounds is more than just training for the youngsters. It’s an important avenue for learning new songs! In 1999, two ornithologists in western Canada heard white-throated sparrows singing a shorter song. Instead of the triplet “can-a-da,” they heard a doublet, “can-a.” Over the next few years, scientists studied older recordings of the white-throat’s songs, and made new observations, too. In ten years, by 2019, the new song had been adopted as far east as Ontario. Currently, you can only hear the original song in the farthest east populations.

How did the new song spread so quickly when these sparrows breed clear across Canada? They learned from each other on their wintering grounds and then took the new “slang” back home in spring. This goes against traditional wisdom, that young birds learn to sing from their fathers before they leave home. Song spread is facilitated because male sparrows from all over are extra concentrated. They tend to stick to the north end of their winter range—poised for a rapid return to claim a breeding territory in spring—while females go farther south to avoid competition with the males.

Just singing a new song isn’t enough to make birds successful, though. If it’s not recognizable to your own species, or sounds weird, a new song might hurt your breeding success. In this case, females prefer the novelty of the males’ new song, and this reinforces the change.

I’d heard about the white-throated sparrow’s changing songs before, but it wasn’t until I investigated the young birds’ jazzy riff that I realized it had taken over so completely. I’ve been trying to shoehorn their summer songs into the familiar “Oh, sweet Canada” mnemonic, and attributing variation to lazy birds. Now I know that something much more interesting is going on. Just like the sparrows, I learned something new in their winter habitat.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.