Under Pressure

Pressure ridge on Lake Winnipeg by Heather Hinam

With the ‘polar vortex’ that held much of North America in its frigid grip last week, it was interesting for this ‘girl of the north’ listen to southerners goggle about phenomena that I’ve been experiencing for most of my life.

I found one event, in particular, rather interesting. Last week, the media and thus a large portion of the population, was introduced to the concept of ‘frost quakes’. Torontonians were rattled out of their beds by thunderous booms that shook parts of the city at random intervals. Soon the headlines were reading that it was so cold in Canada, the ground was cracking.

Lake Winnipeg Cliffs

Large crevasse in the rock, likely split apart by frost action

Having spent a number of winters on the shores of Lake Winnipeg, where  temperatures regularly dip below -30C, I’ve seen first-hand the power of ice and its ability to snap rock in two. Ice expands and contracts with temperature fluctuations. It also becomes less flexible as it becomes colder. Water that finds its way into fissures in the rock or soil can push so hard went it freezes – especially if the temperature drops quickly – that the substrate buckles under the pressure. Here, along the lake, the limestone cliffs are full of cracks forced open by winter’s icy push. Still, these earth-shattering events are extremely rare. You don’t usually see new cracks on a yearly basis.

However, there is another type of frost quake, or ice quake, as I prefer to call them that happens considerably more often. Based on where the events were reported last week along Lake Ontario, I’m willing to bet that it was this type of cryoseism  that residents heard for the most part. While the ground doesn’t crack very often, the ice on the lake does. On large lakes, like Lake Winnipeg or Ontario, a sudden snap of the ice can sound like a cannon shot, nearly knocking you off your feet and rattling windows in their panes. While it’s still not something you experience everyday, such quakes happen on Lake Winnipeg fairly regularly.

That’s because this 23,750 sq km lake freezes completely to a depth of at least a metre every year. That much surface area can’t solidify into one piece. So it freezes into floes that knit together much like the tectonic plates of the earth did when the crust first formed. Like the earth’s crust, the lake’s surface is full of fault lines, or pressure ridges.  These giant cracks can run for kilometres along the lake and usually form in about the same place every year.  Some ridges, known as stamukhi, are grounded along the shoreline, where ice that is held fast to the shore meets the free-flowing ice of deeper waters, while others run along over top of varying depths.

Even frozen, the lake is very much alive and pressure ridges are the sites where this is most noticeable. It’s along these lines that the ice floes move, sliding along, away from and into each other. A particularly violent collision is like a mini mountain building event and along with an ice quake, you will also see a ridge of ice has been pushed sometimes more than 2 meters into the air.  More often, however, the two floes simply press against each other, expanding and contracting like long, drawn-out breaths as the temperatures wax and wane. Eventually, the pressure overtakes the compressive strength of the ice and the ridge snaps in a startling bang that is often followed by the gentle whale-like ‘whoom’ sounds of the pressure waves dissipating through the rest of the ice.

As fascinating as they are, pressure ridges are also dangerous places to be. The ice floes can slide away from each other just as quickly as they can come together and loose plates of ice can trick the unwary into thinking they are still on solid ground. A number of commercial ice fishermen have been lost through shifting ridges over the last century on the lake.

Unless you live along a lake that freezes regularly, Ice quakes are truly something few people get to experience. So, I’m glad that our recent continental cold snap gave more people the chance to learn a bit more about this fascinating phenomena and remember just how powerful nature can be.

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Writing in the Snow

Qali Growing up, I would hear people quote this statistic: “Eskimos have more than a hundred words for snow.” Actually, I still hear people rattle off this little ‘fact’, especially in winter.  However, there are a lot of problems with this statement, not even including the fact that the indigenous people of North America’s tundra and Arctic regions are known as Inuit, not Eskimo. No, what really grates on me about this blanket statement is the implication that it’s somehow weird to have so many words to describe one thing.

When it’s something that makes up a very large part of your daily life during a significant portion of the year, why wouldn’t you take the time to describe it as accurately as possible? The English language has several words for rain: showers, downpour, drizzle, sheets, so why not snow, especially in light of the fact that it sticks around a lot longer than its warm weather counterpart.  Actually, as a Canadian, I’m surprised that we, as a population, haven’t developed more words beyond flurries, blizzard and slush to describe this white stuff that blankets much of the country for four to six months out of the year.

To do that, we have to turn to other cultures and languages. While the true count is well under one hundred, many Inuit dialects have several useful words to describe the incredible variety of snow that we can encounter throughout the course of the winter.  For those of us who live in forested areas, one handy word to know is qali. It refers to the snow that builds up on the branches of trees, glazing limbs in white and making it look like someone attacked the woods with a decorator’s bag full of royal icing.

I was lucky to have learned several Inuit terms for snow as part of some of my undergraduate university courses and like many people who study winter ecology, they’ve been part of my lexicon ever since. So, it took a bit of digging to figure out where the word qali comes from. According to William Wonders, who wrote the book Canada’s Changing North (2003), the word originates from the Kobuk Valley Inuit of northwestern Alaska, along the edge of the treeline.

Qali can range in thickness from a light dusting that could almost be mistaken for hoar frost to heavy globs of wet snow that drag beleaguered limbs to the ground under its unrelenting weight. All along that spectrum, it has a significant impact on the ecological community.

Many winter residents are affected by qali. Spruce grouse and squirrels that regularly feed on cones often find themselves driven down to the ground by a particularly heavy layer of qali. The snow-covered branches can be hard to navigate, forcing these species to search elsewhere for food. On the other hand, qali can make some food more accessible. With particularly heavy wet snows, the qali that builds up on young birches, willow and aspen pulls the flexible branches down, bringing the young, tender tips within reach of hungry cottontails and snowshoe hare. These contorted trees may also provide shelter for a whole host of wildlife.

You might not have ever realized it, but if you live in an area that experiences snow, qali has likely affected you at some point and I don’t mean that moment when you accidentally brush up against a laden branch and send an unwanted shock of snow pouring down the collar of your coat. I’m talking about more significant impacts. Qali can be very heavy and often trees buckle under the weight taking down whatever else is nearby, which is some cases are power lines. I know I’ve spent the odd cold, snowy night in the dark, waiting for hydro to be restored.  These qali-broken trees also open up the forest floor to new growth, creating pockets of mini forest succession and driving the forest cycle on a smaller scale.

Snow is an amazing thing and qali is only one small facet in a dizzying array of diversity, which thanks to northern cultures, we’re able to describe in accurate and imaginative ways. So, next time you take a winter walk surrounded by white, take a moment and discover that variety for yourself and maybe even create your own words to describe it.

 

In the Bleak Midwinter

Insulation - chickadee warming its feetIt was minus 40 Celsius with the wind chill the other morning. The bite of the air stung any carelessly exposed skin and the snow squeaked like Styrofoam underfoot. Wrapped up in my shearling coat, I couldn’t help but watch in fascination as a nearby mountain ash came alive with foraging Pine Grosbeaks and the cheerful chirps of chickadees and nuthatches filled the frosty air, reminding me just how incredible these tiny winter residents really are.

Chickadees, for example, weigh not much more than 10 g, about the same as two nickles. Yet, they can survive quite comfortably in temperatures that would leave us frostbitten and shivering.

Winter birds accomplish this seemingly unfathomable feat in a number of different ways. Firstly, they’re wearing a down coat. Those of you who own one know just how warm they can be and for birds, that insulation is part of the standard package. Feathers are a remarkable insulator. Comprising only about 5 – 7 % of a bird’s body weight (that’s half a gram on a chickadee), the air trapped within them makes up 95% of that weight’s volume, creating a thick layer of dead air that traps heat generated by the body, preventing much of its loss even on the coldest of days. Many winter residents grow a thicker winter coat, much like mammals, augmenting their feather count by up to 50 %. Fluffing feathers increases their insulation factor even further (about 30%), making them a very efficient way to keep warm in the winter, so efficient, in fact, some birds, like Great Gray Owl can actually overheat in the summer.

While some species, like Ruffed Grouse and many owls, grow feathers, along their legs and feet, like fluffy winter boots,  most songbirds’ legs are bare, thin sticks of sinew, blood and bone exposed to the elements. Although birds can tuck these delicate structures up into the warm cover of down when temperatures really plummet, most of the time they’re out in the open. So, why don’t they freeze and why isn’t all of a bird’s body heat lost through these naked limbs? Bird legs are marvels of biological efficiency, having been streamlined by millennia of evolution into sleek structures with very little muscle and few nerves, using instead pulley systems of tendons and bone to accomplish movement. These tissues, along with their scaly coverings have very little moisture and are less likely to freeze than flesh and skin.

Birds also have cold feet. Using a common natural system called a countercurrent heat exchange, our feathered friends keep their feet upwards of ten to twenty degrees colder than their core body temperature. Countercurrent Heat Exchange System in a bird's leg. by Heather HinamWarm arterial blood on its way to the feet pass right next to colder blood coming back towards the body through the veins. Heat wants to reach a point of equilibrium, so warmth from the arteries passes into the veins which carries it back into the body. Because the flows are running opposite to each other, it’s impossible for the heat balance to ever reach equilibrium, so by the time the blood gets to the feet, it’s much cooler than when it entered the leg and all that precious body heat has been kept where it needs to be, in the core.

However, as most of us who have experienced a true northern winter know, a coat alone isn’t always enough. There has to be heat to trap in order for insulation to work over the long term. To generate that heat, many winter birds shiver constantly when they’re not moving. Ravens, whose feather count isn’t as high as some of its more fluffy distant cousins, actually shiver constantly, even when flying, the repeated contractions of their massive pectoral muscles acting like a furnace. Powering that furnace takes energy and cold-weather specialists meet those needs by upping their metabolic rate, in some species, to several times their normal levels. As a result, food is always a going concern in winter.

Many winter residents can only forage for food during the day, so keeping the internal fires burning at night can be a challenge.  Finding a warm place to settle in for the night reduces those metabolic needs.  Densely-packed spruce boughs or old tree cavities are perfect nighttime microclimates and many birds use them. Chickadees will often take it a step further, piling as many fluffy little birds as possible into an old woodpecker hole to share body heat, which may just be too much cuteness in one place. Ruffed Grouse take advantage of the insulative capacity of snow in a somewhat comical way. One cold nights, the birds dive head first into a drift and tunnel deeper into the snow, creating a cave known as a kieppi. Temperatures inside the kieppi can hover just around the freezing mark, even when it’s minus thirty outside.

So as we close in on the shortest day of the year and sink deeper into the cold clutches of winter, take a moment, now and then, to marvel at those tiny survivalists outside your window. Much of the technology that keeps us from succumbing to winter’s icy grip was adapted from them. Nature truly is our greatest teacher.

I Want to Talk With the Animals

I’ve always had a bit of a Dr. Doolittle complex; but then, I think most of us have at some point, at least those of us who read nature blogs. Maybe it’s a by-product of having grown up with Disney movies full of talking animals and birds that sing along with your happy tune. Whatever the cause, I’ve always been looking for ways to make a connection with wildlife.

I feel very fortunate to have succeeded on a number of levels. Years as a field biologist have led to encounters of all sorts, from young owls hanging out in my pocket  and pulling moose out of sink-holes to being warned off by a pack of coyotes or nearly run over by an escaping fawn.

Lately, it’s been all about the birds. My local black-capped chickadees and red-breasted nuthatches have me trained. A few years ago, they descended on me one autumn afternoon, demanding food like kids on Halloween. One thing led to another and it quickly became a yearly tradition. When the days begin to grow shorter and the supply of insects dries up, my little masked bandits show up at the kitchen window, fluttering in front of the glass, letting me know it’s time to get out the sunflower seeds.

It’s an experience that will never get old: sitting on my back porch, hand out, while a half dozen or so chickadees flit between my outstretched fingers and the nearest trees, shuttling a seed or two back to their favourite hiding place. What fascinates me is how they come to trust in the first place.

It’s not uncommon for an animal to overcome its fear of humans for a good food source; but to come back year after year and to even seek me out in the first place is pretty remarkable when you think about it. However, for these species, a good memory can be the key to a long life. Resident boreal songbirds go through boom and bust cycles when it comes to food and will store the overabundance during the good times to help them through the leaner months. The trick is remembering where they put it.

Birds, as a rule, don’t have much of a sense of smell, so they can’t seek out food caches by picking up their scent, like a dog or a squirrel. They have to remember their hiding places. Chickadees are pretty good at it, finding a little over half of their nooks and pilfering any others they find by accident. Corvids, like ravens, crows and jays have even sharper memories, with some species being able to remember up to 80% of their cache locations. Like most of us, they use landmarks. Studies with Clark’s Nutcrackers have found that the birds take note of the relative position of rocks and branches to mark their troves.

Good memories in corvids also extend to who to trust and who is dangerous. Long-term studies at the University of Washington have shown that crows can remember people who’ve done them wrong for many years, harassing them whenever they get too close. So, if crows can do it, why not chickadees? But, how does this knowledge survive over several years? While crows can live for decades, the average lifespan of a chickadee isn’t more than two years.

Well, you know what they say, word travels fast. Chickadees are social birds with complex methods of communication biologists are only now getting a handle on. Those same studies in Washington found that crows pass on their knowledge to others within their range. Chickadees likely do the same. In fact, they manage to pass on their knowledge to others beyond their species. Turns out, nuthatches can apparently understand ‘chickadee’, at least when it comes to information about predators. I wouldn’t be surprised if they’re also picking up information about food by hanging around their ever-chattering flocks.

Once the snow melts, these flocks will disperse, scattering into the shadows of the forest to start their families for the year. In the meantime, their cheerful noise will bring warmth to the coldest of our winter days even if I can’t help but wish I could get in on the conversation.

Suspended Animation

My world is getting quieter. As winter descends on the boreal forest, it’s like a veil of silence wraps around us, stilling all motion, save for the whisper of the wind across the newly-formed desert of snow.  One by one, the waterways stop, frozen in time, held captive by the solid grip of truly frigid temperatures.

Around here, the last body of water to succumb to this relentless creep of ice is the great Lake Winnipeg. Staring out over its endless expanse during the summer, it’s hard to believe that this inland ocean, the tenth largest freshwater lake in the world, finally gives in and stills beneath over a metre of ice.

It’s not a quick process and it actually starts a lot earlier than most of us realize. As the days get shorter and the air gets cooler, heat from the lake is slowly released into the atmosphere, often creating lake-effect precipitation, but that’s a story for another day.

As the water cools down, it becomes denser because the molecules’ natural vibrations slow and they cluster together. This denser water sinks deeper into the lake, letting warmer water rise to the surface and release its energy to the skies. This cycle continues until all the water in the lake reaches the same temperature. For freshwater, the magic number is 4 degrees Celsius, not zero, like you may have guessed. The water still freezes at zero degrees, but from 4 degrees on, the water molecules start to form the lattice work that ultimately becomes ice and at this point, this water is less dense than the rest of the layers below it, keeping it at the surface, where it starts to freeze.

At over 23,000 square kilometres, Lake Winnipeg doesn’t go quietly. November is a restless month, with flinty skies and often driving winds. Wild weather churns up this giant, but relatively shallow cauldron, breaking apart the fragile skin that forms on the surface, forcing it to start over.  Still, the cold eventually wins. The ice thickens and sheets knit together, sealing off the water below as it creaks and moans like a giant humpback whale trapped below the surface.

By the end of December, the ice will usually be thick enough to hold the weight of snowmobiles and tank-like Bombardiers used by the commercial fishermen to get to their harvesting grounds. By January, it’s strong enough to hold the weight of fully-loaded semi-trailers charging across the barren ice roads to deliver goods and supplies to towns that in summer can only be reached by air or by boat.

All the while, the lake is still very much alive beneath its frozen shell, reminding us of its presence with rattles and muted groans rising up from the depths. It’s a sound I never tire of hearing because it reminds me that the lake I love is still there, restless and waiting to be released with the warmth of spring.

Diving into things

Northern Hawk-owl We’re heading into owl season around here, my favourite times of year. Of course, after nearly 15 years chasing these denizens of the dark around in the forest, I may be a little biased.

Actually, as soon as the snow blankets the ground, I go into owling mode, scanning tree tops and hydro poles for distinctive silhouettes. This heightened awareness comes from the knowledge that winter and early spring are the best times to spot one of the more unique members of the Order Strigiformes.

I’m referring to the Northern Hawk-owl (Surnia ulula). Their name alone suggests that they may be something a little different. They’re actually quite aptly-named. Unlike most of their fluffy, almost stocky cousins, these smallish owls are really quite streamlined, with relatively small heads, long tails and slightly more narrow wings. They’re also diurnal, hunting during the day, instead of exploiting the darkness like most other owls.

In the winter, these little stealth bombers come out into the open, perching high on the tops of spruce trees or old snags, sweeping the area with their eyes and ears, searching for scurrying rodents. Their sharp-eyed gaze can spot a vole bouncing over the snow up to 800 m away. When they find one, watching them pounce is a sight to behold. Most owls are relatively slow flyers, almost floating to a stop over their prey before they plunge to the ground for the final kill.

Hawk-owls are another matter. They usually don’t slow down. If the vole is on the surface of the snow, they don’t stop at all, snagging the morsel on the wing and swooping up to a perch to settle in with their kill. Their flight patterns are actually more like that of a Goshawk or a Cooper’s Hawk and that, coupled with their daytime habits, likely led to their common name.

These unusual birds are one of the least-studied of northern owls. Most of what we know about them comes from studies done in Scandinavian countries, where banders have worked diligently for decades to understand their owl populations. Here in North America, only about a dozen nests have been studied extensively.  The fact is that they’re hard to work with. Although you can spot them with a fair bit of regularity during the winter, hawk-owls disappear into the bogs and old burns to breed during the spring and summer months, making them hard to find, right at that period in their natural history that we want most to understand.

What we do know is that they like tree cavities for nests, laying their eggs in old woodpecker holes or burnt-out snags.  Like their northern neighbours, the Great Gray Owl and Boreal Owls, their reproductive success and thus their population numbers are likely tied to the cycling abundance of their rodent prey. Indeed, every now and then, large numbers of these birds will wing their way south out of their normal range in search of food, stirring southern birder populations into a frenzy. Still, we don’t really understand the mechanisms that drive them yet.

The scientist in me abhors this unknown and wants to work up a study and dive right into fray, teasing out patterns from the apparent chaos. However the writer in me likes that there are still mysteries left in our world.

Brainy Birds

Common Raven - Corvus coraxWhile they make their home in the north woods all year round, I tend to notice ravens more in the winter. Without the distraction of countless other species vying for my attention, I’m drawn to the stark beauty of their black wings against the blue sky of a winter’s day.

We also have more of them this time of year. It’s not uncommon to see over a hundred in a day as those who were breeding further north make the trip south to my neck of the woods to join their brethren scavenging for food among the ice and snow.

Out on Lake Winnipeg, they tend to follow the commercial fishermen, descending in the dozens onto the ice after the men move off, cleaning up the leftovers before the wolves and foxes get there.

Ravens have had a pretty bad reputation throughout much of history.  Feared as harbingers of ill omen, ghosts of the murdered, or souls of the damned, ravens have haunted literature from ancient myths, right up to Poe and Steven King. Still, not all feared this big black bird. Some cultures, especially North American first nations, revere the raven as a creator and trickster.

The species comes by this last attribute honestly. For a bird brain, ravens are very intelligent, having one of the largest lumps of grey matter of any avian species. For starters, they have an excellent memory, a skill that comes in handy when having to rely on stashes of food to get through the winter. Ravens and other members of the corvid family hide extra food, when it’s in abundance, in caches (i.e. under a rock, wedged in a tree, etc.). It gives them something to get them through the leaner times. If they were a dog, they would sniff out the food later, but unlike mammals, ravens, like most birds, don’t have much of a sense of smell. So to find their caches, they have to remember where they put it.

Ravens take it one step further, not only remembering the location of their caches, but keeping an eye on their flock mates in case there’s the opportunity to lift somebody else’s food.  This risk of losing your stash to a neighbour has resulted in ravens demonstrating the ability to deceive, going through the motions of hiding a cache, but leaving nothing behind, a fascinating display of insight.

Having a good memory opens the door for all sorts of learning. Ravens are good mimics. My mom told me a story of a raven they had at the zoo in Winnipeg who had learned to talk, mimicking the patrons just like a parrot.

Probably the most useful expansion on a good memory is the ability to use trial and error to learn new things. A number of studies on raven cognitive abilities have demonstrated this talent. Birds have been shown to use tools and solve complex problems to obtain food, even working together towards a goal, like tag-teaming a dog, one distracting him from his bowl, while one of the birds eats, then switching roles.

However, the manifestation of their awareness and intelligence that fascinates me the most, is their penchant for play.  Ravens, especially the young ones, like to have fun, sliding down snowbanks and kicking snow onto unsuspecting passersby from their perch high up on a building. Many times I’ve watched, transfixed, as a pair of them raced after each other through the sky, whirling around before locking talons in mid-air and barrel-rolling among the clouds.

On other occasions I’ve been lucky enough to spark one’s interest. One quiet winter evening, I called out to one, mimicking the soft caw that seems to be a contact call. Usually they ignore me, but this one didn’t, coming closer and landing in a nearby tree, echoing my calls. As we chirped and croaked back and forth to each other, he cocked his head and I couldn’t help but get the feeling that we were both wondering what the other was thinking.