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.