Jumpin Jack Flash

If you’ve ever spent any time in North American forests east of The Rockies, you’ve seen it, a sudden flash of white, that snags your attention before disappearing into a tangle of vegetation.

White-tailed deer  (Odocoileus virginianus) are very aptly named.  The bright, snowy fur on the underside of their tail is impossible to miss, especially because they often wave it in the air as they bound away from you.

This behaviour is called ‘flagging’ and it’s an instinct that kicks in only hours after birth.  To a human observer, its purpose is a little hard to understand. Why would an animal that is otherwise very well camouflaged wave a big flag at a predator that essentially shouts “I’m over here!”.  Because it seems so counter-intuitive, flagging has been the focus of a number of studies, but researchers still have yet to come to a consensus in regards to why they do it and who are they doing it for: their fellow deer or whatever is trying to make them dinner.

Some biologists believe that by flagging, their tails at the approach of a predator, deer are signalling each other and maintaining the cohesion of the group while at the same time confusing their stalker by making it hard to pick out an individual in the group.

The problem with that assessment, however, is that deer will flag when they’re by themselves or when others in their group can’t see them. I’ve seen it many times as I’ve approached them. You know you’ve taken a step too far when the tail goes up, even if the deer doesn’t immediately run away.

The consensus now is that this flashy signal is for the predator, not other deer. But, why wave a white flag when you could be better off blending into the background? Deer flag most often when they’re out in the open and when you are still a good ways off. It’s essentially their way of telling the predator (or you) that they’ve spotted the danger and are prepared to outrun it.

The hard part is figuring out how predators respond to such a signal. Humans and domestic dogs don’t understand the language and are poor models of how a coyote or wolf might behave. No one has managed to collect data on how natural predators respond to flagging However, deer aren’t the only animals to use an ‘I see you’ signal when they’ve spotted a predator.

Many ungulates, like Thomson’s gazelles, pronghorn, and springbok will leap from all four feet, straight up into the air, in a behaviour called stotting, when they spot an approaching predator. Like flagging, this jump signals to the predator that its been seen, then takes it one step further by also communicating that they are more than capable of outrunning the threat.  It seems to work. Studies in Africa have found that cheetahs will abandon hunts more frequently when their target stots and if they still choose to initiate a chase, they’re less likely to win.

Like with most animals, these relatively simple signals are just a small part of a whole array of behaviours that make up a complex web of communication between predator and prey. So, take the time to be observant. With patience and intuition, you can learn the language and open your eyes to a whole new level of understanding of the world around you.

Bright-eyed and Bushy Tailed

After charging out of the gate early and then several false starts later, spring is finally settling in here in the boreal forest.  It’s been a strange year so far and I can’t help but wonder worriedly at the changes I’ve been seeing in the climate these last several years.  Between summer-like temperatures, then snow and frost, it’s been hard to get true sense of the seasons.

The animals, however, tell a different story. Seasonal behaviour in most species is hard-wired to a certain degree, often tied in less to temperature and more to changes in the length of daylight.  While, unseasonably warm or cold days can either speed up or slow down nature’s clock, the overall pattern remains relatively constant.

For me, one of the first harbingers of spring comes in the form of a frantic ball of red fur streaking through the forest.  Red squirrels (Tamiascurius hudsonicus) are active all year, racing from tree to tree, industriously gathering up anything remotely edible and either devouring it on the spot or stuffing it away in a midden, the heart of their territory, for leaner times.

This flurry of activity takes a definite upturn as the darkness of winter gives way into the softer, longer light of spring.  Here in the boreal, that can be as early as the beginning of March, when patches of snow-free ground begin to appear on the forest floor. Females are only reproductively receptive for a day, but she’s not shy in giving her potential suitors a head’s up, bounding through their territories, days before her estrous, reminding them of their impending opportunity.

Squirrels aren’t known for their social grace or a warm and welcoming demeanor. These feisty little rodents are fiercely territorial, expressing their displeasure at anyone and anything that crosses into their domain with an insistent rattle that ricochets off the surrounding trees like a miniature jackhammer. Mating season is the only time of year that edginess eases somewhat and males welcome the presence of female intruders into their little patch of forest, hoping for a chance to pass on their genes. However, if another male crosses over the boundary, all bets are off and the territory holder immediately lays into the interloper, the two of them bounding through the forest in a flurry of fur and furious chattering.

Females are equally antisocial and once the deed is done and she’s been inseminated, the donor is no longer welcome on her doorstep. Like many mammals, red squirrel females raise their young on their own, tucking themselves away into an old woodpecker hole to set-up a home for their young.

Gestation is only a little over a month, so it won’t be long before the squirrels in my neighbourhood find themselves with new mouths to feed. The young are born blind and pink, completely dependent on their mother’s milk and warmth, tucked up in the whorls of grass with which she’s lined their nest. Nests are established opportunistically, and squirrels will just as easily set up house in a nest box intended for birds as in a natural cavity. In my years working with saw-whet owls, I’ve stuck my hand into my fair share of squirrel’s nests and come out with a palm full of very warm, very naked little babies.

They grow quickly, however, putting  on almost 2g/day until they’re ready to venture out on their own just over four months later. By that time, the little guys are fully furred, smaller replicas of their parents, with an innate ability to scamper through the trees without a second thought. That’s not to say there isn’t a bit of a learning curve. One can only marvel at their resilience when watching a juvenile plunge 40 ft out of the tree to the ground, dust himself off and climb right back up like it was nothing more and a stubbed toe.

Resilience is key if you’re a red squirrel. Once they leave the nest, times are tough. By the end of the summer, they are no longer welcome on their mother’s territory and must take up residence someplace else. Competition is fierce and predators, like marten, goshawks and owls are just waiting to make a meal of them. Still, squirrels are scrappers and if they can get a foothold in that first year of life, they’ll likely be just fine. So, spring settles in with fits and starts after an unnervingly warm winter, I can’t help but take comfort in the ringing rattle outside my window, reminding me that even with all that is changing around me, the seasons still cycle and life finds a way to move ever forward.

Sounds of Silence

Walking through the winter woods I can’t help but feel an overwhelming sense of closeness with the world around me. Snow is nature’s greatest silencer, muting the world as it bathes it in white and it’s this silence that breeds a feeling of intimacy with my forest brethren. Shrouded by heavy bows and intermittent shadows, I feel my senses stretch through the quiet, reaching out for any sign that I’m not alone in my wanderings.

As I make my silent progress, I find myself wondering how the other inhabitants of the forest perceive this winter world. Whenever I get into one of these moods, my mind usually strays to the white-tailed deer, a species I’m fortunate to meet often on my woodland rambles.

We’re about the same size, a doe and I, and their soft, forward-facing eyes and expressive faces make them easy to relate to.

Though I know she could easily outrun me (especially since I’m a rather slow runner, even for a human), we have a bit more in common than we might first realize. White-tailed deer and humans perceive the world in much the same way. Deer, for the most part, are just a lot better at it.  They have to be. When you live you life under the constant threat of predation, it’s in your best interest to develop a sophisticated arsenal of early-warning systems and deer have plenty.

In deer, the nose knows everything that’s going on around them. With over 290 million olfactory receptors, deer can detect the faintest whiff of danger, even more accurately than their canine pursuers (who only have about 220 million). Both, however, seriously outstrip humans, with our rather paltry 5 million. Where do they put them all? The nasal region of both cervid and canine skulls is actually quite long and full of thin bones in a delicate scroll-work called nasal turbinates. In the living creature, these bones are covered with olfactory epithelium (skin with scent receptors) that picks up the tiniest of molecules. When actively sniffing, they fill their nasal cavities with as much air as possible, giving scent molecules a better chance of being picked up.

To further improve things, deer have a small, fluid-filled sack lying just on top of the palette called the vomeronasal organ (or Jacobson’s organ). This seems to function in a very specific type of scent detection – pheromones, something most mammals use in abundance and deer are no exception.  Whether we have such a functioning organ too is still being debated, but there is evidence that suggests it might play a subtle role in our lives.

Whenever I come face-to-face with a deer, I’m always drawn in by those liquid doe-eyes and this is one place where we have a bit of an edge over our four-legged friend, at least when it comes to how we see our world. Most people will tell you that mammals, especially ones that are active in the dark, don’t see colour. That’s not entirely true. The retina of deer eyes do have cones (colour receptors); they just can’t quite distinguish the same spectrum. A deer’s world is tinted in blues and greens, which makes sense, considering their main concern is picking out the right plants to eat. Still, don’t think you’re invisible to them as you walk through the woods in a blaze-orange vest. Recent work has found that they can pick out at least a hint of these longer wavelengths and with a visual range of 300 degrees while standing still and eyes that are highly sensitive to the slightest movement, a deer will notice you long before you even know you’re not alone.

Besides, if the eyes fail them, the ears wont. No matter how carefully I tread, I know that somewhere, the crunch of my footsteps is being collected by the large, rotating pinna of a deer’s ear. Their range of hearing is considerably better than ours, picking out much higher frequencies than we could ever hope to detect. The wide placement of the ears on the head and their ability to rotate them independently also make it possible for a deer to triangulate the source of a sound, much like an owl.

I know that I will never experience the world on the same level as any of my fellow forest inhabitants, but on a silent, snowy afternoon, I can’t help but want to try.

 

Size Really does Matter

Autumn is a magical time, full of the fresh scent of fallen leaves, crisp, blue skies and the plaintive grunts of horny ungulates.

Yes, folks, it’s mating season in the boreal forest, known in the deer world as the rut. As the days get shorter, hormones start running rampant. Lean, muscular bodies have reached peak condition after a summer’s diet of green, leafy vegetation. Pheromones are being produced in vast quantities to be splashed onto every available surface. But, for deer and moose, it’s really all about the antlers, which have now been scrubbed clean of their protective velvet layer to gleam in the warm autumn light like a warriors sword.

Unlike what us human females like to tell our potential mates, size, in cervids, truly does matter. It’s all about who has the biggest rack.  Think about it, ladies, which would you be most attracted to: the young, scrawny male with little knobs that just barely make it past his ears, or the magnificent bull with antlers stretching over a meter from tip to tip? In female ungulates, the choice is ingrained: bigger is better because she’s not just seeing an impressive display, she’s seeing good genes.

Those antlers are what behaviourists call ‘honest signals’. Only males healthy enough to carry around all that weight can display them. Take moose (Alces alces), for example. Antlers of a large bull can span up to 5 ft (1.5 m) across and weigh 60 – 85 lbs (27 – 39 kg).  Male moose spend 25% of their energy in the summer just growing them, using more resources than females put into gestating young.  Antlers grow fast, starting to form in mid-summer and reaching full size by September. In fact, moose antler is the fastest growing bone tissue known. Growing it is one thing; then they have to carry them around for another few months.

It’s for that reason, that antlers are such a reliable signal of male health and why they are so attractive to females. If the male is strong and healthy enough to carry around 70 lbs on his head just to look good, he should father some healthy calves.

Another theory explaining why females choose males with larger antlers and other ornaments is known as the ‘sexy sons hypothesis’. The idea is that females choose males with the largest antlers, longest tail or brightest colours because they figure they will father sons who are equally attractive, ensuring they will pass on their genes to future generations. Either way you look at it, it has resulted in some pretty amazing looking animals.

These racks aren’t only for show. While in most cases, it can easy to determine a winner when two competing males cross paths, sometimes the match-up is too close to call on sight alone. In those situations, a fight usually breaks out. Like two hockey players, they launch at each other and lock heads, pushing and grunting until one eventually gives up. Although death is rare, fights can be dangerous. You can get cut, or gouged or, like the one pair of bull elk I watched, one can push the other into oncoming traffic.

For this reason, male ungulates spend a lot of time sizing each other up before engaging in any combat and they’ve evolved some more sophisticated ways to do that besides standing around comparing sizes. Those pheromones they splash about contain a lot of information on each individual’s  health and status. Many species, like white-tailed deer (Odocoileus virginianus), create pheromone markers all over their territory by scraping bark of small trees and rubbing scent glands at the base of their antlers onto the exposed wood, leaving their calling card. This allows other males entering the territory to decide if its worth taking this guy on without having to see him.

As the days grow shorter still, the furor eventually comes to an end. The females are with calf and the hormone levels in males peter out, leaving them exhausted, but hopefully satisfied. Having served their purpose, the antlers drop off, likely affording a great deal of relief, but it’s only a few short months before the next rack starts growing and the cycle starts again.

Can you hear me now?

Somehow I’ve managed to make a good part of my living for the last decade standing around in the dark. Owls have been a source of fascination and a subject of study for me for quite a while now.  I’m not alone in that fascination. Many people are drawn to their seemingly all-knowing eyes and wise faces.

I hate to destroy any long-held beliefs, but owls aren’t really all that wise. There are many bird species (the crow family, for example) that have much greater levels of intellect.

That doesn’t mean owls are any less remarkable. This group of birds has evolved some amazing adaptations to help them make the most of their nocturnal realm.

What I find most fascinating is their ability to hear in three-dimensions. While we can perceive depth with our eyes, they can also do it with their ears.

Owl Skull (without sclerotic ring) showing ear openings.

The secret is asymmetrical ear openings. In most animals (ourselves included), the ears tend to be at approximately the same level on either side of the head. However, in the especially nocturnal owl species or ones that predominantly use hearing to locate their prey, one ear is usually higher than the other.

As a result, sounds do not reach both ears at the same time. It’s this delay that allows the bird to figure out where the sound is coming from.  They can be quite precise, detecting differences in timing up to 30 millionths of a second. When an owl hears a sound, the medulla of the brain creates a three-dimensional mental map of where it’s located. They then hone in on that point by moving their heads until both ears are hearing the sound at the same time. When they reach that point, they are facing their prey. Adjustments can be made while in flight, moving their heads until they’re lined up to strike.

Because they are operating at such a high level of precision, it’s important to have the best hearing as possible. In many owls, like this Great Gray Owl above, most of their face is made up of a disk of feathers. This facial disk acts like a satellite dish, funneling sound to the ears. Muscles under the skin allow them to adjust the shape of the disk as needed to get the best reception. Cup your hands around your ears and you’ll get an idea of how it works.

The size of this disk of feathers is a pretty good way to quickly assess just how nocturnal an owl species is. Larger disks, relative to the overall size of the face (like in Boreal Owls or Barred Owls), means that the species tends to hunt mostly at night.

Great Grays are a bit of an exception.  They have huge facial disks, but hunt mainly at dawn and dusk. These owls, however, hunt prey that are hidden by layers of snow in the winter. Like hunting in the dark, they can use their ears to pinpoint a vole running under the snow up to 150 metres away! It gives a whole new meaning to good reception.

Tiptoeing Around the Subject

I was out for a walk in the snow the other day wearing my mukluks, something I haven’t done in a while and I forgot just how much fun it is. Because they have no sole, it’s very much like walking around in your socks, but much warmer and your feet stay dry. What I like about it, however, is how much closer you feel to the world you’re walking through. I spend most of my days in hiking boots, which while they afford a great deal of support, also separate you from the ground quite a bit. Mukluks are about as close as you can get to walking through the woods barefoot, which in -20C, is not something I’d recommend.

Anyway, this little expedition got me to thinking about another set of fun words that don’t likely come up in conversation all that often. They’re words that pertain to foot posture.

Not all animals walk the same way. When we’re talking about mammals, we can usually place them into three categories: plantigrade, digitigrade and unguligrade. Today, we’ll start with digitigrade. Dogs (like the wolf, whose print in in the picture) are digitgrade. It means walking on one’s toes. In digitigrade animals, the heel is permanently lifted up off the ground. Take a close look at your dog or cat’s legs and feet. You’d notice the four toes, then the pad in the middle. That’s not the heel. Work your way up a bit and you’ll find it, a hard lump a few inches up the foot.

Plantigrade vs Digitigrade feet

Dogs, cats and other mammals like weasels are essentially walking on their toes. The reason for evolving this type of posture has to do with increasing their stride length. Pay attention next time you’re running. You’ll notice only your toes make contact with the ground. By getting up on our toes, we lengthen our stride and as a result, can cover larger distances. Digitigrade mammals do this all the time, which is why we won’t be outrunning any wolves anytime soon.

All this from a walk in the woods…

The Joy of Obscure Words

After over 10 years as an academic, I forget sometimes that I’ve accumulated a vocabulary that most other people have never heard of. Every now and then, I’ll throw a word into a conversation or program that will leave people gazing back at me blankly, brows furrowed in confusion.

The thing is, I don’t do it to impress anyone. I use them because there just isn’t another word out there that better describes what I’m trying to say.

Subnivean is one of those words. I figured that since we’re on the subject of snow, (and we’re getting more of it as I write this), it would be a good time to bring it up.

Subnivean is a great word. Once you break it down, it’s quite simple. Sub = under, nivea = snow. Basically, it refers to anything that is found under the snow. Most of the time, it’s used to describe the habits of animals that are found living under the snow.

There are actually quite a few of them. Small mammals, like mice, voles, lemmings and shrews are too small to grow a winter coat of fur when things get cold. That much hair would make walking a challenge.  Instead, they take advantage of a rather ubiquitous source of insulation: snow. The white stuff is an excellent insulator. On days out here when the mercury drops down well below -30 degrees C, the temperature at the bottom layer of snow, right where it’s in contact with the ground, is still hovering around the freezing mark, a much more comfortable temperature for our furry little friends.

That bottom layer of snow is quite a bit different from the rest of the layers above it. It’s referred to as the pukak layer (an Inuit term) and is usually very crystaline, almost like sugar. This type of structure makes it easy for mice and voles to create an entire network of tunnels completely hidden from the hungry eyes of predators.

That doesn’t mean they are completely safe. Predators like weasels and mink can follow them down into the tunnels, while foxes and owls listen for them from above (a story for another day). Still, with lots of readily-available food, shelter and relative safety, being subnivean isn’t a bad way to be for a small mammal.

However, there are reasons to come ‘top-side’ now and then. The pukak layer can be compacted by snow collapsing or from people walking or driving snowmobiles over it, making the substrate impenetrable.  It can also get hard to breathe down there. With all sorts of critters running around in what is essentially a closed environment, CO2 can build up, making it necessary to punch a few air holes to clear things out (above).

So next time you’re out for a walk in the snow, keep your eyes peeled for the subtle signs of our subnivean neighbours.