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.

Advertisements

Back Home on the Range

Plains Bison and Keystone Species by Heather HinamI’ve fallen behind a bit on my posts of late; but in my defence, I’ve been very busy teaching and for the first time in a while, travelling.

In my travels, I had the opportunity to branch out from my usual boreal forest/aspen parkland region and explore a whole new host of habitats.

One of those were the grasslands of southern Saskatchewan. These regions are often passed over as ‘boring’ by travellers in Canada who prefer the more obvious grandeur of the Rocky Mountains or coastal regions.

However, I can assure you that the mixed-grass prairie that carpets a swath along Canada’s border with Montana is a truly remarkable region, full of breathtaking beauty and a whole host of fascinating species you won’t find anywhere else.  The stark landscape is alive with grasses rippling in waves, dotted with islands of sagebrush, the odd tree and the carefully manicured lawns of prairie dog towns.

This is the landscape that once was home to the plains bison. For thousands of years, millions of these thundering ungulates roamed not only grasslands, but at least 45 other ecoregions as the largest-ranging ungulate in North America, shaping each region as they went. You see, bison are what are known as a keystone species.

Keystone species are those whose impact on the world in which they live is greater than what you’d expect from its population or, more specifically, its biomass. These are species who fundamentally alter the habitat they live in, affecting the lives of myriad species around them.

In their heyday, these largest of all North American herbivores were the linchpin holding the grassland ecosystem together, providing food for a host of predators, including entire civilizations of humans and by shaping the very structure of the landscape and thus affecting the day-to-day lives of a large proportion of prairie species.  I was fortunate to learn about these relationships from Wes Olson, former Parks Canada warden who has lived and worked with bison for decades.

Bison literally left their footprints on the landscape. Their heavy bodies pressed their hooves into the earth, leaving singular holes (called pugging) that bled into trails, churning the soil and breaking up the thatch from previous years for new growth and allowing a greater diversity of plants to get a foothold. Ploughing their noses through the winter snow to graze the coarse remains of the summer’s grass left short-cropped lawns that would green up faster in the spring, offering much-needed nutrients to both the bison and other prairie grazers like jack rabbits and pronghorn. These patches also would get a boost of nitrogen from urine the bison released regularly into the ground.

These winter grazing lawns were also great places for animals that need visibility to congregate. Birds like Sharp-tailed grouse and sage grouse could use them in early spring as dancing grounds, or leks, where males get out and literally strut their stuff in the hopes of finding a female.

A bison’s penchant for wallowing also had a significant effect on the landscape. When a 2000 lb animal rolls around on the ground, it tends to leave a mark. These dust bath pits were often the only spots on the prairie to retain open water for any length of time and become important draws for many dozens of species from insects and frogs to top carnivores like badgers and coyotes.

Every part of the animal was used. Human predators, like the Blackfoot people of southern Alberta would use everything from the hide to the meat to the bladder for protection, food and other tools. Animal predators, like coyotes would feed on the flesh. Scavengers, like vultures and badgers, would take what was left. Rodents would gnaw on the bones in their search for the calcium missing from their diets. Dung beetles and burrowing owls would make use of the bison patties for food and olfactory camouflage respectively, if humans didn’t scoop them up first for fuel in this wood-less landscape.

This intricate network was torn apart as European settlers moved across the continent. By the late 1800s, a combination of habitat loss, conscious extermination efforts and just plain wastefulness saw a population of several million reduced to tiny, isolated herds. Today, the wild population numbers about 30,000 individuals, restricted to parks and conservation areas.

However, the bison is not extinct and the threads are starting to re-knit themselves in more and more places. Herds have been thriving in Elk Island and Riding Mountain National Parks for years, making their mark on the aspen parkland. Plains bison were also reintroduced to Grasslands National Park in southern Saskatchewan in 2009 and already their effects are being felt. Slowly, after over a century, this much-abused landscape is starting to heal. Though it’s hard, if not impossible to turn back the clock, some of the interactions and relationships I’ve described are reforming and places like Grasslands remind us just how complex and resilient nature really is.