The Snowshoe Hare (Lepus americanus)
The quintessential winter animal, the snowshoe hare is a North American species found across the more northerly states and into Canada. Snowshoe is an apt name for this hare, as their back feet are particularly large and lined with stiff fur, allowing the hare to spread its weight over the snow and stop them sinking into snowdrifts, just like the outdoor gear. Their large feet are the perfect adaptation for surviving in their snowbound habitats, allowing them bound and leap through snow to forage and escape predators with ease. Their paws also have thick fur growing in between the pads to insulate them from the freezing snow. They are also well known for camouflaging themselves depending on the season, with their summer coat being a rusty brown, gradually changing into a full white wintery coat to blend in with the snow as the seasons turn colder and the days get shorter.
Fortunately, this species is very common and classed as least concern by the IUCN, with a stable population trend. However, as a species adapted to cold seasons, there is a real possibility that climate change could impact them in the future.
Evolutionary leaps: how rabbits and hares came to be
The snowshoe hare is part of the Leporidae family, consisting of hares and rabbits with their close relatives the pikas making up the order Lagomorpha. The earliest representatives of modern hares and rabbits is estimated to be a small ground dwelling herbivore called the Hsiuannania, of which only fossilized fragments of teeth and jawbone have been found in China. Most palaeontologists believe all rabbits and hares originated in Asia and gradually spread over the world, where their ecosystem role as common prey for many carnivores forced them to evolve the ability to leap and move quickly. The fossils of ancient species of rabbit show that they had much shorter hindlegs and less developed ankles than modern species, highlighting the evolutionary pressure that forced rabbits to evolve into fast agile animals.
A hare of two seasons: habitat and ecology
Snowshoe hares live in the boreal and upper montane forests of North America, covering Newfoundland to Alaska, to Sierra Nevada in California to northern New Mexico, across to North Carolina and Tennessee and up into Canada. There are many different subspecies depending on the location.
Perhaps the most important feature the hares look for in their preferred habitat is the presence of a dense layer of shrubs which is essential as cover from the many predators that hunt them. In fact, field studies have shown that the presence of this dense layer of vegetation is more important than the reliability of food sources or the presence of competing species when it comes to habitat choice for the hare.
The hares are a fairly shy species and as they are mainly nocturnal or crepuscular (meaning they are active at dawn and dusk), they spend most of their days resting in shallow depressions in the ground called forms that they excavate from clumps of vegetation.
Due to the vast changes in the seasons in their range, they eat a diverse diet depending on the weather. In the bountiful summer they graze on herbaceous plants, grasses, forbs and sedges and in the leaner winters they eat twigs, bark and small stems, leaving distinct browse lines in the vegetation called hare lines.
Ups and downs: population cycles in the Snowshoe hare
Snowshoe hares experience well studied peaks and troughs in their population numbers every 8 to 11 years, with their numbers dropping 25 times lower in some years. No one exactly knows why this happens despite a range of field studies, although several suggestions have been put forwards, including fluctuations in food availability, changes in the number of predators or a combination of both. After a slight lag, changes in the number of snowshoe hares is followed by a matching change in predator numbers, a well-known phenomenon called the Lotka-Volterra model. There’s a lot of rather boring math behind this model, but it basically explains the interactions between species in biological settings, in this case predator and prey. As prey (ie: the snowshoe hare) decrease due to predation, they breed less and so are harder for the predator (ie: the Canadian lynx) to find. As a result, after a short time, the predator species begin to decrease as they are unable to find sufficient food and so die through starvation or begin to breed less. Free from heavy predation, the hare numbers begin to increase as they are freer to browse and breed, and so there is now more food available for the predators, and the whole cycle starts again. Of course, as is often the case with fancy mathematical models, this model doesn’t take into consideration other variables like interaction with other species, weather or disease, but it does give a clear example of predator prey interactions and is well studied in the snowshoe hare and the Canada lynx.
A coat of many colors: how do Snowshoe hares change with the seasons?
When the weather begins to cool across the snowshoe hares’ range, their brown summer coat begins to moult and slowly becomes a fluffy white winter coat. But how does this change come about?
By studying their genomes and the genomes of closely related species, researchers identified their genetic variation in a gene encoding for coat pigmentation that is switched on when the hare begins to moult as winter approaches. This gene is activated as the day lengths grow longer, signalling the beginning of the colder months. Further mapping of related species genomes found that this is a relatively recent (at least in evolutionary terms, so several thousands of years ago!) acquisition gained through interbreeding with black tailed jackrabbits, another common species that lives in the same range as the snowshoe hare.
The fluffy white coat makes this species an iconic winter animal, but is global warming going to make this a thing of the past? Or could rising temperatures put this common species at risk of decline?
In recent years, bright white hares against distinctly snowless forests have become an increasingly common sight. This is due to winters becoming milder across much of their range, and although hares have adapted coats depending on the seasons, this change is triggered by day length instead of temperature. This means they still moult into their white coat in Autumn, regardless of whether the temperatures are cold enough for snow, leaving them vulnerable to predators who can now spot them very easily against the brown undergrowth. This could possibly even lead to the white coat being increasingly phased out of existence, as individuals that keep their brown coats for longer could have an increased chance of survival.
However, recent studies have shown this may not be the case. Researchers tracked 347 hares with accelerometers through the Yukon across several seasons and found that those hares with mismatched coats actually thrived instead of being caught by predators. In fact, hares with mismatched coats had their chances of predation slashed by 86.5%! Researchers hypothesised that this is due to reduced time spent foraging as previous studies have suggested that hares will choose to colour match their environment, with brown hares choosing to stay on brown coloured tiles 91% of the time in controlled experiments. It is also likely that they need to forage less as their thick winter coat keeps them very well insulated, meaning they need to expend less energy moving and keeping warm.
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