The Beaver, Emblem of Our National Parks
Text: Denis Comeau
© Parks Canada
Forillon National Park's landscape is divided by a number of small rivers and streams that serve as habitat to a wide range of aquatic and terrestrial animals. The prevailing conditions of a great number of these waterways are suitable for the building of dams and the establishment of colonies by beavers. In fact, since the park was created, the beaver population has continued to increase to the point where it now constitutes an important component of Forillon's ecosystems.
A Rodent Without Equal
The beaver is a large rodent and the only representative of the Castoridae family in North America. It generally lives in family groups or colonies. The beaver is essentially a semi-aquatic species that lives on and around streams, rivers, marshes and lakes. This environment offers it some protection against its predators by allowing it to move about with ease, something that it accomplishes with much more difficulty on land.
Tree eaten away by a beaver
© Parks Canada
The beaver's most remarkable characteristic is its tail, which is flat and covered with scales. Beavers use it as a prop while felling trees, a rudder while swimming, a fat reserve in winter, and even an alarm mechanism when warning other members of the colony of any imminent danger.
The beaver's eyes are equipped with a nictitating membrane, or third eyelid, to protect them underwater. Its nostrils and ears are also adapted for life underwater, closing automatically when the beaver dives. These adaptations, as well as an equally remarkable respiratory capacity, allow it to remain underwater for up to 15 minutes!
Apart from trappers, the beaver has few enemies. The black bear, the coyote, the river otter and the Canada lynx are some of the species that occasionally prey on the beaver, particularly when it leaves the protection of its pond.
A Growing Population
In Canada, the trapping of beavers for fur is generally controlled through issuing licenses and limiting trapping seasons. The beaver population is relatively stable today, but this was not always the case. Beaver fur was highly prized in the 17th century, and uncontrolled trapping up until the end of the 19th century led to a wide-scale decrease in their numbers and even to their extermination in some areas.
Today, beavers are found from northern Mexico all the way to the edge of the arctic tundra. In fact, they have settled in almost every area where a suitable combination of water conditions and vegetation types can be found.
The park's beaver population has grown since the park was created in 1970. That year, only seven colonies were thought to exist. When the Park's Natural Resource Conservation Service undertook an aerial survey in 1980, the number of colonies had increased to 23. In 1991, 73 active colonies were identified. Finally, a last study in 1996 identified 46 colonies.
The average colony is composed of four to six individuals. The total beaver population of Forillon can thus be estimated at between 184 and 276 individuals. In the park, this corresponds to a density of 0.204 colonies/km 2.
The 1996 inventory showed a drop of the number of active colonies compared to 1991. Even if some hypothesis can be put forward to explain these results, it is difficult at the moment to identify the exact cause of this diminution. New studies will be necessary to define the causes and see if it is a general trend or just a momentary situation.
The end of April in Forillon National Park corresponds to the spring thaw of rivers and lakes. Therefore, it is also the start of a new active season for beavers. Adults, as well as the young born the previous year, work to repair any damage that may have occurred to their dams during the spring freshet. Breeding occurs during the cold season and the kits are born in May or June.
© Parks Canada
Summer is the season of plenty for beavers, who feed on new shoots, as well as tree bark and twigs. They enlarge their ponds at the end of summer to gain greater access to food supplies without having to venture too far from the protection offered by water.
In the fall, beavers build up their food stores for the winter. Food piles are made up of branches which are for the most part submerged in front of their lodges. Another important activity for beavers at this time is the maintenance of their lodges. They cover their lodges with branches and fresh mud which, once hardened, forms a protective shell. The dark brown colour of freshly solidified lodges is one clue aerial surveys use to distinguish active colonies from inactive ones.
In winter, the beaver's metabolism slows down and it eats less.
Beavers generally remain in their lodges and feed on the food stores prepared in the fall and stored under the ice. Mountain maple, trembling aspen, balsam poplar and willows make up the largest part of the beaver's winter diet in Forillon.
The Beaver's Needs
In Forillon National Park, slope is the main factor determining whether a beaver settles on a particular waterway. Sixty-two (80%) of the colonies identified in 1991 were located on waterways with a gradient of less than 3%. Streams with high gradients (i.e. greater than 6%) were for all intents and purposes avoided by the beavers. This is primarily because these swift-flowing waterways impair dam construction and maintenance. Topography is thus an important consideration for beavers when setting up a colony.
The surface area drained by a river, an indicator of its magnitude, is also a determining factor. Beavers are less likely to settle on a river with a drainage area greater than 15 km2, as these tend to be swift flowing. Vegetation, another key component of the beaver's habitat, does not seem to be a limiting factor in Forillon. In fact, changes brought about to the forest cover have probably contributed to the increase in the beaver population.
A Landscape Transformed
Beaver activities have a significant effect on the park's aquatic and forest ecosystems. The building of dams and subsequent increases in water levels affect a site's hydrology, soil and waterside plant life as well as the abundance and diversity of terrestrial and aquatic species that are found there.
© Parks Canada
Once it is built, sediments and organic materials accumulate upstream from a dam. This accumulation leads to an increase in bottom-dwelling invertebrate populations, which feed on this debris. By felling trees at the edge of a river, beavers increase the amount of sunshine reaching it, thus increasing the water temperature. This phenomenon increases plankton density in the water column, and consequently the number of aquatic invertebrates that feed on them.
The first species to benefit from this increase in productivity is the brook trout. As well as increasing the amount of food available, beaver ponds serve as rest areas and overwintering sites for this species. But the beaver's activities are not always helpful for fish. In the long run, the accumulating sediments on the pond bottom and the increased water temperatures decrease the amount of dissolved oxygen available for the brook trout. Most researchers, however, agree that the beaver's activities are generally beneficial to freshwater fish.
The river otter, the American mink and the belted kingfisher are among the predatory species found in this environment. They all feed, to varying degrees, on brook trout.
Beaver ponds also attract several species of aquatic birds, such as the wood duck and the black duck, as well as some migratory birds that depend on these newly created habitats to feed, breed and rest.
The changes brought about to the pond's and the adjacent bank's plant communities also benefit some large mammals. Moose and white-tailed deer feed on the aquatic plants and the abundance of young shoots that appear after a beaver colony has settled. As for black bears, they are more interested in the abundance of wild berries that can be found in these new forest clearings.
Living in Harmony with the Beaver
However admirable the beaver's work, it is not always compatible with human activities. Dams can cause serious damage if they are built near trails and roads. The park's Natural Resource Conservation Service uses a number of techniques to resolve these conflicts while at the same time making sure it accommodates the beaver's needs.
One technique involves placing drainage pipes through a dam to maintain the water at an acceptable level. Erecting an artificial dam for beavers to build on is another technique used to keep them from constructing their dams against a trail or road. As a last resort, if none of these methods prove effective, the Natural Resource Conservation Service can consider relocating the beaver colony.
An Increasingly Important Species in the Ecosystem
Apart from man, the beaver is probably the species that modifies its environment the most. In Forillon National Park, the expansion of beaver colonies contributes to the creation of transitional forest communities and wetlands.
Considering the forest surface that a colony may affect and the number of active and inactive colonies counted in the park, it was estimated that close to 14.6 km2 of forest have been affected by the beaver (6% of the park's total area). This demonstrates just how important this species is as a component of forest renewal in the park's ecosystem.
In 1991, the ponds created by active beaver colonies represented almost 18 ha of lentic habitats (still waters). This is approximately equivalent to the total surface area of all the lakes in the park.
A Conservation Challenge
Preserving the beaver population and that of all species in the park, as well as controlling and regulating conflicts between humans and nature, are part of the mandate that Parks Canada implements to manage wildlife. By protecting beavers in Forillon National Park, they also give the park's many visitors the opportunity to observe this species in its natural habitat.
The Natural Resource Conservation Service regularly follows up on colonies which are found to be in conflict with the park's installations. An update of the status of Forillon's beaver population is undertaken every five years. This information serves to monitor population fluctuations and evaluate the need for further research on this species. Such studies are essential to increasing our understanding and improving the management of our ecosystems and their components.
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