A Thing With Feathers

Even if you can somehow go through your entire life without ever seeing a bird, chances are very good that you will still have some experience with feathers. Whether displayed in a  hatband, stuffed into a pillow or quilt or tied together at the end of a duster, feathers are a fairly ubiquitous part of the world around us and certainly the defining characteristic of the group of flying vertebrates we know today as birds.

But, have you ever given much thought to where they came from?

As it turns out, feathers have been around a lot longer than most people realize. As paleontologists find more fossils every year to slot into the puzzle that is the evolution of life on this planet, the picture becomes clearer and stories start to make sense.

When it comes to the story of the evolution of feathers, the first thing you have to remember is that birds are modern dinosaurs, having evolved from the lineage known as Theropods, whose ranks include those Jurassic Park villains Velociraptor and Tyrannosaurus rex.  However, what didn’t make it into the movies was the fact that, at the very least, Velociraptor was not only ferocious, but fluffy. At first, this detail was inferred from the discovery that many of its ancestors were feathered and some, like the bizarre, bi-plane like creature Microraptor gui, could fly. Then, a discovery of quill nobs, a trait seen in modern birds, on the forearm bones of one specimen confirmed it. Now an accurate representation of Velociraptor is something like a sleek, predatory ostrich.

Even more recent discoveries have put the assumption of a scaly hide in Tyrannosaurus rex into doubt. While they haven’t found specimens of this iconic dinosaur with feathers yet, a cousin from about 125 million years old China, named Yutyrannus most definitely was feathered. About the size of a bus, these are the largest feathered dinosaurs known to date.

So how far back do feathers go? In time, we can trace their existence at least 160 million years to chicken-like dinosaurs called Anchiornis, but these critters already had the highly complex barbed feathers we see in modern birds today.  Most evolutionary biologists agree that feathers likely started out as single, hollow,  hair-like filaments that became branched and barbed as needed over time. These have been found in many species, most notably, Sciurumimus, a dinosaur found very near the base of the Theropod branch. Described for the first time just last year, this species shows a spectacularly preserved coat of dense, filamentous plumes. Finding feathers like these near the base of the branch suggests that maybe more advanced Theropods, including T-rex had some kind of plumage. Still, we don’t know just how far back down the tree they go.

The point of origin keeps getting pushed closer and closer to the root of at least the dinosaur’s evolutionary tree thanks to feather filaments being found in some Ornisthischian dinosaurs, like the Triceratops cousin, Psittacosaurus, who are about as far removed from Theropods and modern birds as a dinosaur can be. Actually, they’re starting to find feathers all over the dinosaur family tree, leaving us to wonder if they predate the group altogether. In fact, the genes responsible for taking an undifferentiated plate of keratin and turning it into a feather has been found in crocodilians, who although they are birds’ closest living relatives, branched off from the group well over 250 million years ago.

So what did these prehistoric feathers look like? Structurally, early feathers started out as simple, hollow strands, growing out from a plate of keratin embedded in the skin. More advanced feathers split into barbs, looking like fluffy ostrich plumes. Eventually, those barbs developed tiny barbules that allowed their wearers to ‘zip them up’, turning them into strong, but flexible sheets that eventually were co-opted into airfoils. This same evolutionary progression can be seen today in the growth of every bird embryo.

Most fascinating, however is the fact that paleontologists now know what colour some of these plumes were. Recent work with Anchiornis turned up microscopic pockets of pigment called melanozomes. By comparing these ancient structures to those known today, they managed to work out that not only was Anchiornis about the size of a chicken, it actually kind of looked like one, a bright tableau of shiny black and white spangles with a flash of red on a crest. Who knows, maybe in time, we’ll see our very own field guide to dinosaur plumage. Either way, you can’t help but marvel at these remarkable, ancient, ingenious  and unarguably beautiful innovations of evolution.

In the Bleak Midwinter

It 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. Warm 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.

Restless Heart

To regular readers of this blog, my love of obscure words is not a new thing. Over the last few years, I’ve been creating these ‘definition images’ as my way of bringing life to some of the wonders of nature and the words used to describe them.

Looking back over them all, I realized, much to my surprise, that I’ve crafted more than 70 of them, covering just about every letter of the alphabet. That discovery has led me to challenge myself to visualize words starting with more uncommon letters, like  X, Qand Z. Kind of like an artistic variation on Scrabble.

Autumn has given me the perfect opportunity to address one of my favourite Z words.  It’s another one of those terms that comes up only in the discussion of natural history and animal behaviour and it never fails to raise a few eyebrows if you manage to slip it into regular conversation.

The word is Zugunruhe.

Zugunruhe is a combination of two German words = Zug, meaning to move or migrate and Unruhe, meaning restlessness and it together, the sum is really the combination of the parts: migratory restlessness. For a behavioural ecologist, it’s a word that tends to conjure up thoughts of autumn, or more specifically, late summer.

As the earth lumbers along its orbital path and those of us in the Northern Hemisphere find ourselves canting away from the sun’s warmth, many creatures get antsy. Birds especially are seized by a sudden disquiet and activity levels skyrocket. Sleep patterns change and if the individuals are kept in a cage, they start orienting their activity in the direction they should be migrating in. Most species go through a period of excessive feeding, needing to pack away as much energy as aerodynamics will allow for the journey that inevitably lay ahead. We see it all around us in the clouds of blackbirds roiling through the air or flocks of geese descending on a recently-harvested field. This period of restlessness is referred to as Zugunruhe by biologists who study animal behaviour and it’s a phenomenon observed both in the spring and in the fall, just prior to the mass migrations that move millions of birds along north-south flyways over the continent.

Here, in the boreal forest, it’s a phenomenon that usually starts in August. Our summers are relatively short and as soon as breeding is over, the preparation of the twice-yearly journey gets underway, especially in songbirds, who have to travel thousands of kilometres to Central and South America. With their time here so fleeting and the journey so long and fraught with danger, you can’t help but wonder, why go through all the trouble?

Why not stay in the tropics, where the weather is favourable and save all of the energy and risk associated with long-distance travel? The answer to that question likely varies to a certain degree between species; but evidence suggests that food, or rather the lack of it, was likely the driver behind the evolution of long-distance migration in many birds.

Most of today’s migratory species likely evolved near the equator, enjoying consistently tolerable weather and relatively abundant food. However, as populations started to grow and segment into different species, the pressure on food sources grew to a point where the survival of some depended on searching out new resources. The only place to go was away, into the temperate zones north and south of the tropics. Those that did, discovered abundant resources, millions of insects, and a glut of fruit and vegetation. The problem was it only lasts for a short period of time, forcing those explorers to retreat back to the warm haven to the south during the winter months.

Over millenia, these paths have been extended and entrenched by generations of birds winging their way along now well-established routes.  As those paths have become increasingly ensconced in the collective memories of each species, so has the irrepressible need to travel those routes that spurs everything from hummingbirds to harriers on their way twice a year.

With migration in full swing here in Manitoba, the period of zugunruhe is actually over; but once balance of night and day swings back into the favour of the light, the millions of birds enjoying the warmth of their winter homes will feel the inexorable pull once again, the restlessness building until one day, they’ll have no choice but to take to the air and find their way back to us.

It’s a Hard-Knock Life

There isn’t much else in the world that’s cuter than a baby Northern Saw-whet Owl. I should know; I handled dozens of them over the course of my doctorate research. Between their huge, blue, soulful eyes and the round, fluffy, ewok-like body, they’re guaranteed to evoke an ‘aww’ out of even the hardest-boiled egg of a person.

Still, most people will never have the opportunity to see one, at least not in their juvenile plumage. They’re notoriously hard to find.  Northern Saw-whet Owls nest in old tree cavities, moving into empty woodpecker holes and other crevasses in rotted out trunks. To study them more closely, researchers put up nest boxes in the hopes of coaxing them into more accessible real estate. It’s a lot easier to climb a ten-foot ladder up to a nest box than to have to figure out a way to get 25 feet up into a poplar or worse, a hydro pole.

Even once they’re out of the nest, they’re difficult to spot. Being not much bigger than a coffee mug full-grown, these little owls rely on camouflage to stay safe in the forests and woodlots where they make their home.  Their first line of defence when threatened is to go stock still against a tree trunk or in a mess of branches. It’s a very effective manoeuvre.  Adult saw-whets have stripes of brown and white on their breast feathers and spots on their heads that break-up their profile, helping them melt into the shadows. I can’t tell you how many times I’ve tracked a radio-tagged bird to their daytime roost and still couldn’t spot the little guy among the leaves. The brilliant white V on the forehead of juvenile birds is to help parents find their mouths in the dark of a nest cavity. Still, in daylight, this natural beacon manages to blend into the dappled sunlight on the foliage.

Adult male Northern Saw-whet Owl blending into the background.

So, any time I get to spend with these little guys is a treat, one that I never take for granted. It’s always such a pleasure to get to observe their individual personalities up close.

Don’t let their size and adorable expressions fool you. These are tough little birds. They have to be. Life for a Northern Saw-whet Owl is hard from day one. Females lay their eggs two days apart, but start incubating before they’ve completed the clutch. As a result, you end up with a nest full of young where the oldest may have a ten day head start on life over the youngest. In years where the small mammal population is high, the provisioning males can make their nightly quota of about seven or more prey items a night, making it possible for all the young to make it out of the nest. However, in years where food is scarce, that age difference suddenly comes into sharp relief and it’s not uncommon to find only one or two of the oldest nestlings surviving out of a clutch of 4-6.

Even if they make it out of the nest, life doesn’t get much easier. After a month crammed into the nest hole with mom and all their siblings, you’d think these newly-fledged saw-whets would want to move on and take advantage of their new-found freedom as quickly as possible.  However, despite having fully-feathered wings by the time they leave the nest (unusual for owls), juveniles tend to hang around the homestead for another month or so. They spend their days tucked away in the shadows in nearby trees and their nights calling insistently for food deliveries from their already beleaguered father, their mother having taken off around the time the oldest hit 21 days for a much-needed break.  During this post-fleding period, young saw-whets practice flying and refine their hunting skills.

Eventually, it’s time for them to strike out on their own into the great unknown. It’s actually a great unknown for us researchers as well. Despite a number of long-term banding programs for the species all over North America, we still don’t have a very good handle on saw-whet owl movements outside of the breeding season.

So every year, my colleagues across the country and I will keep adding new nest boxes and checking the ones we have, spending as much time as we can peering into the lives of these adorable and enigmatic owls in the hopes that one day we might unravel a few more of their mysteries.

* If you would like to entice owls to your backyard, let me know, and I’ll send you the plans for building a nestbox.

Flying with Dinosaurs

Since the beginning of January, I’ve had the pleasure of teaching a second-year Chordate Zoology course at the University of Winnipeg. Having taken it at a different school as an undergrad and having taught the labs several years ago, the material isn’t exactly new. However, it’s been a wonderful way to rediscover the fascinating story that is the evolution of vertebrates.

First and foremost, it’s reminded me that we see dinosaurs just about everyday, flitting through the trees, soaring high overhead and gliding across a glassy pond. They’re all around us, bringing colour and music to our world.

Because of my grounding in zoology, the concept that birds are dinosaurs is not new to me, nor is it difficult to understand. However, I imagine for many people it’s a bit of a challenge to make the mental leap from a chickadee flitting among the leaves to a giant Tyrannosaurus rex thundering along a Cretaceous plain.  Still, whether you can see the resemblance or not, the genetic relationship is undeniable. A spectacularly rare discovery in 2007 of intact collagen protein in the fossil leg bone of a T-Rex allowed researchers to compare the amino acid chains within with a database of species we already have sequences for. It turned out that of all the possibilities, from mammals to reptiles, the sequence was most closely related to the collagen sequence of a chicken. This discovery probably would’ve left good ol’ Colonel Sanders with nightmares!

Even without the molecular connection, you can still see the family resemblance. Birds are descended from a lineage of dinosaurs known as Theropods, swift, bipedal predators, like Velociraptor, Deinonychus (pictured above) and the aforementioned T. Rex. While the ones most people are familiar with, thanks to Jurassic Park, are the large, ferocious creatures, most of this lineage were rather small, adapted for running and pouncing on their prey. These adaptations for speed and agility can still be seen in the skeletons of the last remaining dinosaurs, the birds.

They walked on two legs, their limbs swinging back and forth on the fulcrum of a pelvis that looked like part of a bicycle. Over time, that pelvis shifted, the individual bones fusing and getting stonger to withstand the strain brought by high speeds while maintaining its light weight. In fact, weight reduction was the order of the day in the evolution of birds from their theropod ancestors. Bones, overall, got smaller, lighter, hollowing out into tubes that were, and still are, reinforced by thin struts called trabeculae. The pectoral girdle got both smaller and in some ways, more rigid. Where the scapulae were freed up to allow the arms to swing out like flapping wings, the clavicles fused, forming the furcula (wishbone) and the sternum developed a deep keel, giving more space for what eventually became flight muscles to attach.

Still, the most striking feature these dinosaurs had in common with the ones we see today was feathers. That’s right, Creighton missed that little detail. Many theropods, Velociraptor included, had feathers. They started out as long, thin fibers that offered the minimum of insulation, gradually developing into the differentiated flight, covert and down feathers we know now. They appeared at least 160 million years ago, long before Archaeopterix (the first official bird) and even non-avian theropods like Velociraptor and Deinonychus. Paleontologists have found them in numerous species, including a small chicken-like theropod (the whole protein thing is making sense now) named Anchiornis. They’ve even managed to determine the colour of the feathers by examining the shape of the melanosomes (tiny pockets of pigment) preserved in the fossilized remains.

As more and more of these characteristics are teased from the fossil record, I can’t help but hope that one day my field guide to birds includes a section on the species that paved the genetic way for the spectacular diversity we see today.

Thanks for the Memories

As a naturalist, I pride myself in my knack for noticing the beauty in the most mundane of things, from rocks and lichen to a leaf on the ground, to pigeons wheeling about an old warehouse. Still, sometimes I fall into the trap of glazing over something I see everyday.

Magpies are one of those things. When doing bird counts or other surveys, I’ll notice them, but it’s a passing glance and a quick mark of ‘BBMA’ in the notebook that is then quickly forgotten. I’m actually quite embarrassed by this, because magpies are truly remarkable birds.

Part of the corvid family, along with jays, ravens and crows, magpies are changelings and rogues. Their dapper, pied plumage give them almost a formal look that seems befitting of the solemn shadows of the winter forest. Then they flit out into the open and the sunlight transforms them into a dazzling creature, shimmering with greens, blues and reds, like the twinkling lights of last week’s Christmas tree. The structure of their plumage refracts the light, revealing the colours hidden beneath the surface.

That’s not all these birds hide. There’s also a brain under those feathers agile enough to rival the great apes and cetaceans. Like the rest of its family, magpies are not your typical bird brains. Firstly, their brain-to-body mass ratio is actually about the same as that of chimpanzees and dolphins and only just slightly less than that of humans. They possess episodic memory, being able to remember not only where they hid their latest food find, but when they stashed it.  If my knack for constantly losing my keys and pencils is any indication, they might actually be swifter than your average human

Having a good memory is an excellent foundation on which to build intellect. Remembering that the local dog likes to chase birds means that if you bring a friend the next time, one can lure the dog away while the other steals some of its dinner, switching off so everyone gets a turn. Memory allows you to be innovative. If you can remember what does and doesn’t work each time to try something, it’s easier to come up with new ideas.

Magpies are definitely one of the foremost innovators of the avian world, using an array of complex social cues to communicate knowledge of things like resource locations and tool use through generations. Most remarkably, they also appear to be able to remember themselves. These pied pipers are one of the few non-human species who have been shown to pass the ‘mirror test’. It’s an easy test; researchers put a brightly coloured dot under the bird’s beak, in a place where they can only see it if they look in a mirror. More often than not, the magpie will see the dot and try and get it off.

So what does this sense of self mean for a bird? How does it affect their relationship with the world around them? Until we learn to speak Magpie, I doubt we’ll ever know. Still, just taking the time to watch them can yield a lot of insight, whether we completely understand it or not. I know I will always be mystified by one memorable morning when it was revealed to me to just how aware these birds are.

When I was teaching vertebrate diversity labs, our instructor took my fellow TA and I for a walk on campus with a stuffed magpie under his arm. In a clearing, he placed it on the ground. I then watched, astounded, as the local birds quickly began to assemble, edging closer to their fallen compatriot, circling the study skin while bobbing their heads up an down in what could only be described as a display of respect, much like what is observed in elephants. I know many of you are probably thinking that they were just eyeing up their next meal, but they made no move to tear at the carcass and I’ve now seen this behaviour several times with my classes.

Throughout of my scientific career, I’ve been warned against the dangers of ‘anthropomorphism’, of ascribing ‘human’ traits and motivations to the animals we study. While I do realize different brains process things differently, I think we do ourselves a disservice by maintaining that we are somehow fundamentally different than the rest of the organisms we share this world with.  Evolution has been working from the same box of crayons for millennia, remixing the colours as situations dictate. I personally feel it’s rather arrogant of us to think we’re the only ones out there who can claim awareness. So, in this season of resolutions, I’m going to remind myself to take a little more time to appreciate those everyday companions that are so easily taken for granted, to make an effort to see the world through their eyes. I think I could learn a lot from them.

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.

Flying Away on a Wing and Prayer

For weeks now, the air has been full of motion, full of flapping wings and rhythmic calls.  Fall has been rolling over us like an endless wave, washing down from the north along ancient streams with millions of birds at its crest.

We’re deep into migration season here in the north woods. Actually, I’m sad to say that we’re getting close to the end. When it starts in mid-August, it’s a subtle change, a gentle trickle, as species begin to disappear like lights blinking out on a Christmas tree. It begins with the little guys, warblers, shorebirds and hummingbirds that have to make the long trek to Central and South America. One of the first of the larger species to go are the Sandhill Cranes (Grus canadensis), their warbling calls ringing so high up in the sky that you often can’t see them against the clouds.

By mid-September, most of the songbirds are gone and we’re knee-deep in waterfowl, thousands of Canada Geese (Branta canadensis), Snow Geese (Chen caerulescens) and assorted ducks darken the skies and fill the farmers’ fields on their way to the southern United States. Now, in late October, the last of the waterfowl are heading off and Bald Eagles are following in their wake, on their way to places where the water bodies don’t free solid.

In Manitoba, about 85% of our birds migrate, but how do they know when it’s time to leave?

Just like the leaves on a tree and pretty much every other living organism on earth, birds are tuned into rhythms of time, the waxing and waning of day length. As the days get shorter, it triggers a response in their hypothalamus that cascades from the brain through the endocrine system, changing the cocktail of hormones coursing through their veins, resulting in an itch to move that just won’t go away. Biologists call that itch ‘migratory restlessness’ or zughenruhe.

During this period, birds get antsy, staying up well past their normal bedtimes and eating like it’s going out of style. There’s a point to this sudden change in behaviour. Most birds migrate at night and it’s important that they store as much energy as possible for their long flights. In fact, migrants will increase their fat loads to anywhere between 15 and 50% of their body weight, depending on the length of their trip.

Many have a very long way to go, some travelling thousands of kilometres to their wintering grounds. Getting there takes a good sense of direction and birds make use of a lot of different tools. Like the explorers of old, the sun and the stars play a big role in keeping birds on migratory routes that have been passed down for thousands of generation. Because many birds migrate at night, the setting sun offers a quick and easy compass to use for orienting their take-offs. Scientists have confirmed this by studying captive birds and using bring lights as a substitute celestial body. Whenever they moved the light, birds would change their take-off orientation accordingly, ensuring they were headed in the proper direction.

It’s not always possible to see the sun or the stars and once you’re in the air, they become less useful. In many cases, large landmarks, like rivers and mountain ranges serve as highways, guiding the flocks on their journey. However, when all visual cues fail, they still have one more fallback. Deposits of the mineral magnetite in their brains have been found to operate as a built-in compass, allowing individuals to pick up the earth’s magnetic field and orient themselves appropriately.

Studies are still trying to sort out how this all works from a biological level, but there’s no question of its usefulness. Work with homing pigeons have shown that messing up the electrical fields around the birds’ heads made it impossible for them to navigate accurately by scrambling their magnetic reception.

So as you watch a V of geese winging their way overhead, just take a moment to watch them. What you’re seeing is an amazing confluence of adaptations and millenia of evolution that have resulted in one of the most astonishing natural phenomena on earth that can be witnessed just about anywhere by anyone.

One and Done

Winter has been really slow in relinquishing its grasp this year. The snow just won’t disappear and the lakes have yet to thaw. Still, regardless of the temperature, spring marches on. The days get longer, the quality of light and the colour of the sky changes and the birds start to return.

One of the first to get back are the Canada Geese. I usually hear my first unmistakable ‘honk’ somewhere around the end of March. It’s an event I always look forward to. For me, it means that regardless of what it might look like outside, spring is on its way.

They’ve been back for a while now and most have settled in to nest. Canada Geese are a ubiquitous bird, common just about everywhere in North America, so common in some places that they are regarded as pests.

Being so universal, they often go unnoticed, just another part of the everyday landscape that make up our lives.  However, if you slow down and take the time to really consider these big, sometimes brash birds, you’ll discover that they’re really quite fascinating.

Canada Geese have a strong affinity for place, at least females do. Female geese return to where they were born to rear their own young. It makes sense at an evolutionary level when you think about it. If her parents successfully raised her there, then the chances of her having her own brood there are pretty good.

The next problem, then, is finding a mate. If she were to choose one on her breeding grounds, they would end up with a pretty shallow gene pool. Over time, each population would have become very isolated genetically. However, if you’re a goose, there’s another place to look for companionship: down south. Their wintering grounds are like Daytona Beach at spring break, thousands of geese from all over converging on locations along the southern US to fatten up and mingle. A young female goose has a lot to choose from there.  Once she finds the gander she’s looking for, he’s in for a trip back to her home waters every spring for the rest of his life.

Yes, Canada Geese mate for life. This detail of their natural history is probably why both males and females look alike. Unlike ducks, where males have to get out there every spring and attract a female using flashy colours and footwork, geese are a sort of ‘one and done’ kind of species. Over their evolutionary history they’ve apparently lost the need to impress each other.

While he might not wow his mate with dashing looks, male Canada Geese are very devoted partners. With the nesting season started, females have hunkered down to wait out the 28 days it takes for their eggs to hatch.  After laying one egg a day until the clutch is complete, she spends about 23 of the 24 hours in a day keeping them warm. Although he doesn’t share incubation duties, the gander takes up the role of sentinel, guarding his charge with the same diligence that she gives to her role. If any potential threat – raccoon, weasel, coyote, unsuspecting hiker- gets too close, he will bear down on them, wings flapping hissing viciously, beating back the intruder.

So, if you find yourself hiking through goose country, keep an eye out and prepare to duck and cover.

Diving into things

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.