Happy Trails: When Human And Nonhuman Trails Converge

It’s spring, and as snow retreats from the land, we hedonistic Canadians begin to think about our next outdoor adventures—most of which will involve “trails” of some kind. Whether it’s hiking, trail running, mountain biking, climbing, or even a canoe trip, our endeavours will likely follow lines on the map drawn by our species.

 

“Because trails allow light to penetrate where it often wouldn’t, plants use trails to disperse, co-opting animal travellers as vectors for their seeds…” Photo: Paul Jarvis / UNSPLASH

Words: Leslie Anthony

Of course, humans have been creating trails since before recorded time, and in some parts of the world these are employed not for frivolous play, but for the age-old purposes of reaching water, finding food, or moving from one place to another as part of a seasonal migration. Which, no surprise, sounds very much like what other animals do.

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The movements of animals (and once upon a time, all humans), in fact, is the primary behavioural adaptation to variability in time and space of available resources. Depending on their scale, animal movements have been categorized into functional groups (e.g. foraging, dispersal, migration, etc.), and are now studied by biologists and ecologists using a range of methodologies. Since the advent of radio telemetry, satellite tracking, and remote-triggered digital cams that can function unaided for up to a year, we’ve learned much more about animals’ use of trails. Perhaps the biggest takeaway is that wildlife trails can be superhighways for a range of terrestrial—and even aerial—species from insects to megafauna. A recent study in Finland found that certain hawks can see rodent urine—which fluoresces in the ultraviolet spectrum—and thus hunt by following trails from the air.

We tend to see trails we use as our own, but they are decidedly not.

This kind of savvy isn’t unusual in the animal kingdom. As a kid, I spent plenty of backyard time watching ants, beetles, spiders and other small critters that created and used trails of some kind, whether chemical or physical in nature. Ants clearly laid down molecular mojo followed by their mates, but even flying insects tended to follow what seemed to be regular “paths” through gardens and around houses—one of the reasons spiders set up webs in very specific places. Of course, we now know that bees can even communicate routes to other bees who will then fly them flawlessly.

And while the myriad trails of the tiny are a world unto themselves, it’s the trails of larger animals (including ourselves) that we’re both more cognizant of and familiar with. Yet we pay little attention to their finer ecological points. For instance, well-used forest trails create space for flying insects and birds to navigate the understory, as well as sparking a food chain that feeds on the dung of their animals denizens. Because trails allow light to penetrate where it often wouldn’t, even plants use trails to disperse, co-opting animal travellers as vectors for their seeds—whether burrs stuck to fur, or berries consumed at one sunny spot and defecated out at another. This leads to the concentration of food sources along trails for herbivores small and large, in turn providing a reason for sit-and-wait predators to hang around as well.

On a side note, a developing modern problem is the role of trails as corridors for dispersal of invasive plants—by animals as well as humans, which can carry progapules on their clothing and shoes (next time you start a hike at a trailhead, note how far dandelions and other invasives follow you along the trail).

As society evolved, we used trails to connect to other groups of humans, whether for visiting, trade or conflict purposes. Pre-existing animal trails often comprised the most direct routes. But as we created our own passages through difficult terrain or vegetation, many animals were more than happy to use them to expand their own home ranges. This reciprocation continues today. Though we would expect that human use of forest trails might also affect the likelihood other animals would use them, most research shows zero-to-low negative impacts, at least on mammals (ungulates are often a different story as they can associate certain trails with hunting danger). However, human activity can lead to changes in animal behavior and distribution if the level of activity is high enough to cause disturbance.

We change entire landscapes with cities, roads, farming, and exploitation of natural resources, but precisely how does this affect animals and their habitats? Using GPS location data from more than 800 animals, a team of German scientists demonstrated a reduction in animal movements in areas with a high human footprint: mammal movements in these areas were on average one half to one third as extensive as in areas with low human footprints. In another study, zebras—which travel up to 500 kilometres, more than any other mammal—immediately resumed these lengthy migrations in Botswana’s Okavango Delta after a fence that blocked their movements from 1968–2004 was removed.

Where am I going with this? Well, back to the beginning. We tend to see trails we use as our own, but they are decidedly not. Whether they were in use before we found them, or our creation of new routes is now subsidizing the movement of other creatures, it behooves us to treat trails as shared natural spaces, to respect the other creatures likely using them.

Many years ago, a few friends and I spent hours scrutinizing a topographic map for the best place to cut a portage between two lakes in the north of Algonquin Park. We found the shortest low point between them and spent the day brushing out what seemed a fairly logical but oddly un-vegetated 150-metre trail, returning to our camp on the original lake for the night. The next day, we carried our gear across the newly cut portage. Halfway across, with a canoe on my shoulders, I spied a massive beaver waddling toward me with a metre-long peeled stick in his mouth. Of course! This was always a beaver trail between the lakes, and now they could more easily carry bigger lumber on it. I stepped off the trail to let the beaver pass. After all, I was only on an adventure, while he was building a house.

 

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