Jumpin Jack Flash

White-tailed Deer Flagging by Heather Hinam

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.

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Sounds of Silence

White-tailed deerWalking 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.