Approximately 160 kilometres off the east coast of Halifax exists Sable Island—a thin crescent of shifting sand, located at the edge of the Continental Shelf. Dubbed “The Graveyard of the Atlantic” (due to the more than 350 shipwrecks off its shores), the 32-km2 stretch of land is protected and managed by Parks Canada, with all visitors requiring advanced permission from the agency. Indeed, Sable Island is extremely isolated—save for a unique population.
Enter the Sable Island horse. Descendants of equines introduced to the island in the 1700s, this group of 500 feral horses is classified by Parks Canada as “a wild population of a naturalized species.” Specifically, the horses, which are protected under the Canada National Parks Act and the National Parks of Canada Wildlife Regulations, exist with minimal human intervention. They do not receive veterinary care and, importantly, people are not allowed to touch, feed, or interact with them.
This lack of intervention is precisely what attracted to population ecologist Philip McLoughlin, BSc., PhD, to the horses.
“I set out to establish a program aimed at filling a specific niche in ecology in Canada: the individual-based study of a wild vertebrate that lives free from predation, interspecific competition, and human interference (to allow me to focus on the role of intraspecific density-dependent phenomena in ecology and evolution),” he says. “After scouting several locations across Canada, I quickly realized that the horses of Sable Island presented an almost ideal system for the study of population ecology and evolution.”
Since 2007, Dr. McLoughlin, who is an associate professor at the University of Saskatchewan (USask), and his team of researchers at the McLoughlin Lab in Population Ecology have been tracking the “life histories and movements” of each horse on Sable Island with the hope of improving understanding of how individual dynamics can help inform population-level phenomena.
“Our program on island ecology also includes significant work on sea-to-land nutrient transfers and links between seals, seabirds, and horses through vegetation,” he says. “We maintain a program on the successional dynamics of the island and the role of the horse in this system.
Veterinary Practice News Canada spoke to the researcher to find out more about these feral horses and the ways in which his team’s findings could help advance equine veterinary science.
1) What sparked your interest in the Sable Island horse population?
I have been working on Sable Island and with its horse population since my first visit in the summer of 2007. At the time, I was finishing up a project on the famous red deer population of the Isle of Rum in Scotland, which was a program of the University of Cambridge and University of Edinburgh. I am a population ecologist, and I was hoping to launch a similar program here in Canada that would be able to address questions of how natural populations of herbivores might be regulated feedback loops associated with their own density. I remembered hearing about the Sable Island horses as a child, and so I booked a trip to the island to determine if the population and system would be suited for a long-term, individual-based research program. Of course it was, and so began our program of research.
2) Can you speak to level of human intervention that is involved with protecting these animals?
The horses live free and die free, so to speak.
Since the early 1960s, there has been, by regulation, no human interference allowed. This precludes things like feeding or provision of veterinary care. In fact, the horses are classed as “naturalized wildlife” by Parks Canada Agency and are treated as such.
Much like many national parks, policies are in place to maintain a distance between horses and tourists (for safety), including, for example, that tourists do not approach to within 20 metres of a horse. By its nature, research may require approaching wildlife to within closer distances—for example, as we sample DNA from known horses using swabs of dropped feces or to sample for parasite loads, which requires timely collection of samples (especially when sand is blowing about and presents a contamination risk to samples). However, all of our work is non-invasive in the sense that no horses are captured or handled; only watched and photographed. I have several projects where we capture wildlife to track animals (e.g. caribou, moose, wolves), but the horses do not need capture on Sable Island, as we can identify all of them from a detailed photographic database. Additionally, through our survey methods, we can obtain GPS locations of where animals stand once they move on (on their own).
People, of course, have a special relationship with horses—a product of several thousand years of domestication. We are respectful of this relationship as much as we are respectful of the wild nature of this population, which has been free-ranging since the mid-1700s.
3) What has your research revealed regarding how the horses impact the area’s native species?
This is an interesting question. Of course, the horses were introduced to Sable Island, as were cattle, goats, sheep, dogs, foxes, pigs, and approximately one third of all the plant species that exist today. Of all the introduced mammals, the horses are the only survivors.
The horses have been able to live on the island with its current assemblage of flora and fauna for quite some time, but understanding their role in this system is a key question of ours. Certainly the horses must play an important role, as the dominant herbivore and as “predator of palatable plants”—as an agent of disturbance (trampling), but also as a dispersal agent of nutrients and even seeds. To understand this role, we have partnered with Sable Island National Park Reserve and the Sable Island Institute to examine how vegetation may respond to the exclusion of horses in targeted exclosures (the “Fences in the Sand” Program). We are into our third year of the exclosure set-up, and so do not have any results to report at present; however, I suspect people may be surprised by the outcome. Remember, horses can play a role as a keystone predator of weedy introduced plants—especially hay forage—as much as they may act on remaining native species.
What I do know is that we need to develop a better understanding of the role of this now naturalized herbivore in the system, whether they are a stabilizing or destabilizing force, mindful that the Sable Island horse could be both depending on population size.
4) I understand your team was recently awarded a federal grant to study the environmental changes occurring in Western Canada’s Boreal Plains.
This large project is aimed at answering questions of population ecology that cannot easily be answered on Sable Island, but for which some parallels can be drawn. For example, while we are interested in how parasites and disease may act to regulate the horse population on Sable Island, in the Boreal Plains, we are looking at how disease may affect the dynamics of one herbivore population (moose) if the agent of disease is supported by another herbivore population (white-tailed deer, with focus on chronic wasting disease and meningeal worm). There are also no predators on Sable Island, and, for most wild herbivore populations, predation can be an important regulating factor in population dynamics. As such, in the Boreal Plains, we are also studying predator (wolf)-prey interactions.
Both projects have an applied focus, as well. For our work in the Boreal Plains, understanding food-web interactions has very real consequences to food security for northern communities that rely on species like moose for food. Our work on Sable Island has many applications off the island, further to the park’s management goals. For example, we are able to understand how sea-to-land nutrient transfers can link ecosystems, as well as how isolated populations of herbivores may be able to survive even in the face of inbreeding.
5) What are some other research topics McLoughlin Lab is exploring right now that you’re excited about?
The Sable Island project is really taking off right now as we advance on a number of fronts, including work with the University of Calgary on how the gut microbiome of horses may be linked to the survival of horses; insight into the nature of inbreeding and inbreeding depression; and we have many questions regarding food-web structuring and animal behaviour.
The horses are also, as far as we can tell, one of the only populations of horses where we know for certain no ancestor or current horse has ever received antibiotics or modern veterinary interventions, meaning the population presents as a unique model of equine veterinary science.