By Rina Quinlan
Wilder Landscapes Advisor
The Eurasian beaver, Castor fiber had been absent from Britain’s rivers for nearly 400 years before recent reintroductions saw their return to our waterways, both in enclosed areas and in a few free-roaming populations. In my role as Wilder Landscapes Advisor, I can often be found championing their vital role as an ecosystem engineer, slowing the flow of water, re-naturalising river systems and breathing life into wetland environments, but I seldom get the chance to celebrate the unique and unusual adaptions that helps set Beavers aside from other native semi-aquatic mammals such as Otters and Water Voles. Therefore, when I was asked to write about the beaver on World Wetland Day for this week’s theme of a tale of tails I was excited to indulge in learning more about the more unfamiliar features of this enigmatic species.
The design of a beaver’s tail is quite unlike that of any other mammal you might see out in the British countryside; its large, flat, scaly and shaped like an oval with a rubbery hair free surface. This unique physiological adaption is thought to have a multitude of uses, such as helping them to guide their route as they navigate through the water. This also steadies their swim as they carry a recently gnawed branch to engineer a dam, leaving a distinctive bow shaped wake in their trail. The tail is full of tiny blood vessels which help them to thermoregulate in cold, wet environments, and works as a fat storing organ which can as much as double in size between late autumn and spring.
The Eurasian beaver is not the only species of beaver to have frequented our island, in the middle Pleistocene up until approximately 400,000 years ago, the giant beaver, Trogontherium cuvieri would have also made a home in England’s then temperate interglacial environment. However, studies of fossils of this extinct rodent have suggested that it led a slightly more terrestrial life, indicated partly by it not sharing the same distinctive flattened tail of its living relative.
Beavers mate for life and have strong stable family groups, caring and nurturing their young together, who disperse usually around their second year to start families of their own. They are highly territorial towards non-related individuals, and aggressive encounters between beavers cause visual scars on their scaly tails, creating at times, large ‘nicks’ of skin that come away. Males are more likely to have a more impressive array of scars, but this is something we may not see until a higher density of beavers are permitted to swim freely in our waters and need to hold their territory. This tearaway nature of the rubbery tail is also a reason that tail-mounted transmitters for tracking beavers are difficult to keep on them as they are likely to be torn off.
Perhaps more well known, is that beavers use their tails to hit down on the water’s surface when threatened or disturbed. Hearing this distinctive ‘slap’, most likely at dawn or dusk when beavers are active is a good indication that you are in the presence of such an important keystone species and a sound that I hope will once again, become common place across Britain’s rivers and wetland landscapes.