Thursday, March 25, 2021

Protecting Birds from Your Windows

The soft but sickening thud sent out a wave of impacts. Conversation, typing, and higher-level thinking stopped. From four corners of the office, heads instinctively turned toward the sound. Bright morning sunshine streaming through the window illuminated nothing unusual, though. With a mix of hope and dread, I opened the back door and scanned up and down the patio. Nothing. I sighed with relief and stepped back inside.

I’d been expecting to find a small bird—lying either lifeless or stunned and glassy-eyed—at the base of the large row of windows that face the Museum’s back yard. Low-angled sunlight in the spring, in the fall, and early in the day, sneaks under awnings and tints the glass of our windows with stunningly accurate reflections of trees and sky. When little birds try to fly into that scene, they get a painful—and often deadly—surprise.

Birds can collide with windows in any season, but I’ve always noticed an increasing number of those sickening thuds in spring. As waves of migrating birds head north, we see both a huge increase in the number of individuals, and an increase in birds who are new to the neighborhood and more likely to be hoodwinked by windows.

This juvenile cedar waxwing died after flying into a reflective window during the fall of 2011. A bumper crop of fermenting black cherries in the nearby trees made the problem even worse that year. Read more about it here. Photo by Emily Stone.

According to the American Bird Conservancy, roughly half of the birds who hit windows succumb to their injuries or are killed by predators while they’re vulnerable. The thud I heard was from one of the lucky ones who flew away. An estimated 1 billion birds die this way each year.

From the number of calls and emails I get on this topic, I know that these bird deaths weigh heavy on the hearts of many. Not only is it distressing to find feathered corpses outside your home, or to watch the life go out of something so innocent and delicate, but headlines tell us that birds are in global decline due to habitat loss, climate change, and more. Each small life counts toward the whole.

Now that warm days are turning even window washing and yardwork into attractive tasks because they give us excuses to get outside, it’s a good time to think about making your windows better for birds.

Window screens that go on the outside of the glass are one of the best tools for preventing collisions. Not only do they break up the reflection, they also act as a safety net. If your windows didn’t come with bug screens, you can use bird netting from a garden store (meant to keep robins out of your strawberries) instead. Just make sure to pull the netting taut like a trampoline, and keep it at least 3 inches off the window so the birds don’t bottom out.

A purely visual grid can also work well. Using tape, soap, tempera paint, or paint pens, you can add designs to your windows that make the glass visible to birds. If you’re feeling artistic, an intricate doodle would do the trick. Otherwise, using a level and a yardstick, you can simply draw lines. The key is to make the spaces between the lines small enough that birds don’t try to squeak through. For best results, vertical lines should be no more than 4 inches apart, and horizontal lines no more than 2 inches apart. If your casualties include hummingbirds, then use the 2-inch measure all around.

While not practical for everyone, you could make the designs permanent by etching or sandblasting them directly onto the glass. If you’d rather use decals, they need to be just as densely spaced as the grid in order to be effective. A company called Collidescape makes grids of dots and one-way transparent film that can do the job. But those single, elegant hawk silhouettes have been shown not to work. Likewise, past recommendations about how to safely space bird feeders away from windows haven’t stood up to testing.

You can also combine the ideas of a grid and a screen and make “Zen Curtains.” Basically a grid made of cords; they hang down over the glass on the outside of the window. They can be easier to install than paint, longer lasting, and can be aesthetically pleasing. I’ve seen them made from sparkly string with tiny mirrors attached, and the effect was delightful! A simple internet search will turn up both commercial and DIY versions.

Not every window or every homeowner can accommodate these ideal modifications, though. Using a simpler option, or a combination of techniques, is still helpful. At the Museum, we often tape a single length of curling ribbon at the top center of each window. As the ribbon blows and bounces in the breeze, it helps to deter birds. Awnings, external sunshades, and shutters can also minimize reflections. Having flowers and shrubs at the base of windows can encourage birds to dive in for shelter instead of trying to fly through to escape from a predator.

Making changes indoors can have an impact, too. Blinds, shades, or even sheer curtains on large windows change the reflection quite effectively. And my favorite recommendation is one of the easiest: letting your windows stay slightly dirty can cut down on the realism of the reflection.

Recent research found a positive relationship between the diversity of bird species in a neighborhood and the life satisfaction of people who live there. Add that to the reduction in those sickening thuds, and bird-proofing our windows feels like a great way to increase happiness this spring.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, March 18, 2021

Spring is just around the corner—and winter is, too!

The metal studs on my fat bike tires crunched noisily on the trail as I pedaled furiously toward the top of a hill. Reaching the crest, I sized up the view, crouched low over the seat, and zoomed down. The air rushing past my face was chilly, but intense spring sunlight and tough pedaling on the slopes of the Esker Trail near Cable were keeping me plenty warm.

Several sunny afternoons in a row had softened the snow of the expertly groomed trail, and I had started my ride early to take advantage of overnight temperatures in the teens that had solidified the surface again. Now, with a firm, sidewalk-smooth path, gravity-fed momentum carried me almost all the way up the other side.

Overnight lows have frozen the Esker Trail solid, but bright sunshine will make the afternoon feel like spring. Photo by Emily Stone.

A few minutes later, I was reveling in the easy riding when I suddenly found myself tipped over with my left leg sunk up to the knee in drifts. This section of trail was contouring around the side of a steep hill. Winding switchbacks and curves had befuddled my sense of direction long ago, but I knew that the hill must be facing north. On this corner, it was still winter. No glaring sun had hardened the surface, and I’d skidded out in soft fluff. My leg sank into snow that was as light and airy as January.

On the previous, sunny afternoon, the mercury had risen to almost 40 degrees, and I’d been cross-country skiing instead. The fish scales in my kick zone work rather well on warm snow, and I hummed along merrily for a kilometer or two. Then, suddenly I found myself slipping and sliding up a relatively gentle hill. The slope wasn’t getting direct sun, but I could still see light glinting off a coating of ice in the tracks. Once again, even with my sense of direction lost in the winding trails, the iciness of the hill gave away its bearing. In contrast, I had to squint against glare as I began the next downhill, and I almost fell over when a section of slush caught my skis.

Late-afternoon sunshine glints off icy ski tracks at the North End Ski Trail in Cable, WI.
Photo by Emily Stone.

A few days later, I went to bed with the sound of rain and thunder, and woke up to a world dusted in snow.

What I’m trying to illustrate, you may have guessed, is that this time of year is both winter and spring. Sometimes the two seasons are separated by a few feet, and sometimes the difference is in a few hours.

Outdoor enthusiasts pay close attention to this heterogeneity. Fat bikers wake early. Road bikers time their rides to hit the warmest peak of a sunny afternoon. Skiers brace themselves for sudden changes in speed. Maple tree tappers carefully monitor temperature changes, too. They know that the sap flows best when nights are cold and days are warm; when an afternoon feels like spring, but winter returns with the dark.

Nature, of course, has no choice but to factor the fickleness of spring into her calculations. Trees who leaf out early in response to unseasonable warmth may then lose all of those leaves to frost, or may surrender entire branches if those leaves catch heavy, wet snow. They must hedge their bets and not be fooled. According to Bernd Heinrich in his book “Winter World,” “Buds follow local schedules that are dictated by an interplay of cues involving day length, seasonal duration of cold exposure, and warmth. Warmth alone is not enough.”

And warmth can also vary quite dramatically from one side of a hill to the other. North-facing slopes receive very little heat from the low-angled winter sun. Even throughout the summer they remain shaded and cool, with less evaporation than their south-facing counterparts. Eastern aspects are similar, since they receive sun in the morning, when temperatures are lower. Western slopes, however, receive the full blast of the sun at the warmest time of day.

These variations in temperature by space and time are not a global phenomenon. Seasons are a characteristic of the temperate zone. The direction a hill faces only really matters in these same mid-latitudes. Near the equator, the sun is overhead and touches everything, all year. Near the poles, winter sun is too weak to provide much warmth and the summer sun circles around and shines on everything. But in latitudes from the bottom of Mississippi to the top of Manitoba (and the corresponding latitudes in the southern hemisphere) slope aspect impacts sunshine, evaporation, soil moisture, and soil temperature…and the plants who grow there, too.

The variety we experience in the Northwoods—the way you can find an early wildflower in a sunny spot and a late one in the shade; the short scramble it takes to get from a dry oak slope to a damp hemlock ravine; the change from winter to spring and back in a single day or a single corner or a single hill—is one of the my favorite parts of living here. At this time of year, it feels like spring is just around the corner…and winter is, too!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, March 11, 2021

Wood Frog Winter

The snow is melting, the soil is warming…and I can’t decide if that’s good or bad. The classic tracks on my favorite ski trail were in fantastic shape last week, and I may or may not have let out a little whoop on a long, swooping, rollercoaster of a hill. But at least a smidge of my smile could be attributed to the southwest-facing bank that cradled the trail and the happy little mosses there whom the sun had recently unveiled.

Huge thanks to the volunteer groomers at the North End Ski Trail!
Their trail maintenance efforts in all seasons have a huge impact on my winter happiness :-)

Oodles of my favorite beings—like moss--live under the snow, in that magical space called the subnivean zone. Like many enchanted things, the subnivium is ephemeral. It comes into existence once 6 to 8 inches of snow accumulate, and disappears again in spring. I love imagining the scurrying mice, hunting weasels, creeping spiders, and gnawing fungi who stay active down there, as well as the mosses, roots, seeds, insects, and others who sleep soundly under the temperature-moderating blanket of white.

In fairytales, it’s a true love’s kiss that breaks the sleeping spell. In nature, it’s often warmth from the sun. The moss has felt it. Sugar maples are feeling it. Who’s next?

Last fall, wood frogs hunkered down in the duff to wait out winter. In order to wake up early, they don’t dig very deep. Even in the relative warmth of the subnivean zone, this means that the frogs must tolerate being frozen. In the depths of winter, up to 65–70% of each frog’s total body water is ice (any more than that and they’re dead). With the kiss of sun and rain, wood frogs thaw from the inside out.

Recovery is relatively rapid—especially considering what the frogs have been through—but not instant. After a day they can move. After a couple days, they’re ready to mate. But even as the black-masked amphibians hop toward a woodland pool, they still aren’t ready to eat. There are a few possible reasons for this. First, it’s quite a process to freeze and then thaw, and their digestive system may be the last system to come back online. Second, there’s not much food available in April when wetlands’ icy caps have just softened and snow may still rest in the shade. Third, the way a wood frog spends the winter is centered on getting back to their breeding ponds ASAP in the spring. Why waste time searching for food?

I get hungry just thinking about it. Wood frogs stopped eating days before burrowing into their hibernaculum last fall, and they will continue to fast until after they’ve gone through the rigors of breeding. Males have to shout at the top of their lungs, chase after females, grip any prospective mate tightly, and fertilize her eggs—all without a snack. Females don’t sing much, but they do lay between one- and three-thousand eggs more than five months after their last meal.

In thinking about this feat of fasting, I had always assumed that frozen wood frogs weren’t using any energy while in their frogcicle state. I was wrong. Frogs’ metabolisms continue to run very slowly even while they are frozen, and freeze-thaw cycles are quite taxing. Researcher Megan Fitzpatrick set me straight when I called her to talk about a research paper published last August in the journal Global Change Biology, and presented at the recent Wisconsin Chapter of the Wildlife Society meeting.

Working with modeling gurus at UW-Madison, Megan created a model to predict how overwintering wood frogs will fare in the face of climate change. Luckily, she didn’t have to start from scratch. The other researchers had already created models about the subnivean zone and regional weather. Those data could be combined with a few of the major Global Climate Models—the ones cited in the news when we talk about how fast different parts of the world will warm—to predict how soil temperature will increase, and how snow cover will change across the southern part of the wood frog’s range.

Megan took those big models and added frog-specific data from a project in Canada that had measured how much energy wood frogs use over the course of a winter. The frogs had been placed in sealed boxes with comfy bedding, cooled slowly, and then subjected to freezing and thawing while the researchers measured their carbon dioxide output as an indicator of energy use.

(Megan assured me that the cold frogs would already be dormant by the time they froze, and therefore would not make the same agonized face as Han Solo as he was lowered into the carbon-freezing chamber in The Empire Strikes Back. Also, all research labs have animal care and use policies to make sure that the critters are treated humanely.)

That study found that carbon dioxide increased sharply at three points: as the frogs were preparing to freeze; as they responded to freezing, and as they thawed and began normal body function and repair. The longer frogs stay thawed in the fall, and the more times they experience freeze-thaw cycles, the more energy they waste. Somewhat counterintuitively, warmer soils going into winter mean that the frogs expend more energy throughout winter.

I asked Megan to explain how that data becomes part of the model. “We break down the steps and each one becomes a mathematical equation that we can add to the model,” she told me. Steps include things like heat flowing through snow, heat flowing into the frog, ice melting in the frog, and the frog’s response to those temperature changes.

According to Megan’s model, warming soils mean higher energy expenditures for wood frogs during winter. But earlier snowmelt means that frogs will survive winter with a balanced energy budget in most regions—or even come out ahead—because winters will become so short. (Notably, her study wasn’t set up to tell us how climate change will impact the frogs during the rest of the year.)

Not all regions saw a balanced energy budget for frogs, though. In the snow belts of northern Wisconsin and Minnesota—where deep drifts tend to linger—wood frogs are predicted to use about 10% more energy to get through a northern winter by the late 21st century. Megan doesn’t think that will kill the frogs, but what about sub-lethal impacts? One study in Michigan found that females laid fewer eggs after warmer winters. And what if a warmer spring means that their ponds dry up? Science is an iterative process that gives us new questions with each study, in addition to useful answers.

Questions like, “the snow is melting, and the soil is warming…is that good or bad for wood frogs?”

So many of the videos out there are overly dramatic--and talk like wood frogs only live in Alaska. Harumph! This is one is concise at least. Just don't pay attention to the last line "science can not yet explain." Science doesn't know everything about wood frogs, but it knows a LOT!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.

Thursday, March 4, 2021

Shining a Light on Curiosity

Once upon a time, in the cool, dark air of his own backyard, a forestry professor swept the beam of a UV flashlight through the trees. He wanted to know if gray tree frogs fluoresce. They don’t. But when a furry shape found its way into the beam and glowed hot pink, Jon Martin discovered that flying squirrels do.

This serendipitous discovery in May of 2017—spurred on by a bit of previous knowledge and a scientist’s curiosity—sent Jon (a professor at Northland College in Ashland, Wisconsin) and his colleagues on quite the scientific journey.

African springhares (center) are the most recent animals to reveal biofluorescent fur. The discovery that flying squirrels (left) fluoresce hot pink, led scientists from Northland College down a vibrantly glowing rabbit hole. Cyan-fluorescing platypuses (right) are one of their other curious discoveries. Images from Kohler et al, Olson et al, and Anich et al. Compilation by Allison Kohler.

In 2018 and 2019, faculty from Northland College descended into the collections of the Field Museum of Natural History in Chicago to examine the flying squirrel specimens stored there. The interdisciplinary team was determined to learn more about Jon’s discovery that flying squirrels fluoresce under UV light.

After shining their UV flashlights at specimens of all three species of North American flying squirrels and being rewarded by flashes of pink, the next question was “what else?” Previously, opossums were the only mammals known to fluoresce. But, opossums are weird. And although their fluorescence was discovered in the 1980s, no one, it seems, dug much deeper. Where was their sense of curiosity?

The Northland College crew was curious. Would the startling trait be common among other furry critters? As it turns out, platypuses (who are even weirder than opossums) biofluoresce, too, and the Northland scientists published that discovery last October.

During their black light safari through the collections, the scientists logically sought out the cabinet that held Old World flying squirrels, who live in Europe and Asia, as well as “scaly-tailed squirrels,” who aren’t squirrels at all, but small rodents from central Africa with a similar stretch of skin and ability to glide. No glow for the scaly-tailed squirrels. The scientists really didn’t expect EVERY species to fluoresce, acknowledged natural resources professor Erik Olson, as he recapped the story for me recently.

But as the next drawer in the cabinet slid open, flaming orange fluorescence flickered under the flashlight’s beam. “We’ve got one!” someone exclaimed, without even knowing exactly what the drawer held.

The specimens were of African springhares, as it turns out. That discovery was just published in the journal “Scientific Reports.” The authors include Jon, Erik, and also Northland College chemists Michaela Carlson and Sharon Anthony, mammologist Paula Anich, and microbiologist Alissa Hulstrand, among others.

Springhares, I’ve learned, are rabbit-sized rodents who leap like kangaroos, but lack a pouch. They are close relatives of the scaly-tailed squirrels, which is why their drawer was nearby. They live only in Africa, where they forage under the cover of darkness and not much else; not even with friends to help keep an eye out for danger.

On a field trip to the Henry Doorly Zoo in Omaha, Nebraska, the team confirmed that living springhares fluoresce even more brightly than the decades-old specimens. Erik also noted that the springhares—both living and dead—glowed much more vibrantly in person than in the published photographs, where the researchers’ careful, scientific process had captured a narrower range of wavelengths.

There is much left to learn about biofluorescence in mammals. Describing the trait is just the first step, but figuring out what the trait means is quite another process. Does it have ecological benefits? Is it a disease response? Might it be useful for conservation? Or could it possibly have no purpose whatsoever? It will take a bevy of scientists from different disciplines to begin to answer those questions.

“To me it’s just exciting to be part of the description of a trait that was unknown.” Erik told me—especially since the animals themselves are all common and well-studied. “These kinds of discoveries really enhance the sense of awe we have for the natural world; they give us a moment to pause and reflect on the world around us.”

Erik was initially skeptical and cautious when Jon told him about the pink flying squirrels in his backyard. Jon wouldn’t give up, though, and the rest is history. The rest has also been covered in the “New York Times,” published in the “Journal of Mammalogy,” and has captured the imaginations of both scientists and the public.

And it all started…once upon a time…with a particularly persistent forester who let his curiosity run wild in his own backyard.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at Or order it from our friends at to receive free shipping!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is closed, but our Mysteries of the Night exhibit is available online. Connect with us on Facebook, Instagram, YouTube, and to keep track of our latest adventures in learning.