It's spring, and as the snow retreats, 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 are likely to follow lines on the map tracked by our species.
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 seasonal movements from one place to another. No surprise that this sounds very much like what other animals do. In fact, the movement of animals (and once upon a time, all humans) is the primary behavioural adaptation to variability in time and space of resource availability. Depending on their scale, animal movements have been categorized into functional groups (e.g. foraging, dispersal, migration, etc.), and are studied by biologists and ecologists using a range of methodologies. For instance, since the advent of technologies like radio telemetry, satellite tracking, and remote-triggered digital cameras, we've learned a lot more about animal movements. Perhaps the biggest takeaway is that wildlife trails can be superhighways for a range of terrestrial—and even aerial—species from insects to megafauna.
As a kid, I spent plenty of backyard time scrutinizing the movements of 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 that could be read by their mates, but even flying insects tended to follow 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 specific routes to other bees, which will then fly them flawlessly.
While the myriad trails of tiny creatures are a world unto themselves, it's the trails of larger animals (including ourselves) that we're both cognizant of and most 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 supporting a food chain that feeds on the dung of the animals using those trails. Because trails allow light to penetrate where it often wouldn't, these become sunning places for some animals, and even plants use them to disperse, coopting animal travellers as vectors to move their seeds, whether as burrs stuck to fur or berries consumed at one sunny spot and defecated out at another. This leads to a concentration of food sources along trails for herbivores small and large, in turn providing reason for sit-and-wait predators to hang around as well. On a related side note, a modern problem is the role of trails as corridors for dispersing invasive plants—by animals as well as humans, which can carry propagules on their clothing and shoes (next time you start a hike, note how far dandelions and other invasives follow the trail).
As human society evolved, we used trails to connect to other groups of humans, whether for visiting, trade or even conflict purposes. Pre-existing animal trails were often used as they comprised the most direct routes. But as we created our own passages through difficult terrain or vegetation, many animals were also 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 that animals would use them, most research shows zero-to-low negative impacts, at least on most 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 behaviour and distribution patterns if the level of activity is high enough to cause disturbance.
Where am I going with this? Well, back to the beginning. We tend to see trails we use as our own, but they are not exclusive. 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, and respect that while for us they may be a means to adventure, other organisms still count on them for their livelihood.
Leslie Anthony is a science/environment writer and author who holds a doctorate in connecting the dots.