The beaver (Castor canadiensis) is the largest rodent in North America. Their habitat is in small lakes, rivers, wetlands and other waterways. Beavers build dams using woody material to modify their habitat, and they feed on the bark of fast growing hardwood trees. For these purposes they cut down trees adjacent to ponds and waterways, and may travel considerable distances overland in order to find suitable trees for their use.
In Ontario, beavers have been known to eat almost every tree and shrub species available. In the Toronto area, preferred foods and building materials are poplars and willows.
Beaver activity may cause damage to public and private property in the form of flooding or tree damage. Girdled, cut or felled trees may topple over, fall onto other trees, utility lines, or precariously hang over public pathways or roadways. In addition, they often gnaw on living trees just to grind down and sharpen their continuously growing incisor teeth. Dams built by beavers may cause flooding, which in the most severe cases may weaken structures, washout roads, and alter watercourses.
However it is important to note that beaver dams, in addition to creating new wetlands, also reduce erosion, help regulate the flow rates in many rivers and streams, and enhance fish habitat. In this respect, some nuisance and damage should be tolerated.
Source: City of Toronto Factsheet about Beavers
Nature's Architects on the High Park Nature Centre blog.
Some effort is made to protect certain trees by wrapping them in wire. However, some trees, such as the smaller ones growing in the marsh at the north end, would not normally be growing in a marsh habitat and have only survived here because the pond level is not fluctuating as much as it would under natural conditions.
The large willow trees at the pond's edge would not normally live for a long time anyway (for example, not like oaks). They are not native willows, although they are very attractive and do have some benefits for wildlife. Some are falling into the pond on their own, without beaver assistance, and there is one fallen tree in the water that has helped improve the pond habitat for fish spawning, etc.
Some beavers may be roaming ones that have not yet found a place to settle, and they do some tree cutting and then move on. If they were trapped and relocated, others would likely come through and do this again, so no effort is made to trap them.
As you walk along the waterways in High Park, you might wonder why some trees are wearing wire cages around their trunks. This armour effectively discourages beavers from chewing on the trees. You will notice that itís too late for a few trees.
If youíre tempted to think, ďOh, those dam beavers!Ē letís look at it from a beaverís point of view. Beavers have to chew wood to survive. They eat wood for food and to keep their ever-growing front teeth from getting too long. They also fell trees to build dams and lodges. As the largest rodent in North America, beavers are actually grounds keepers extraordinaire.
The dams beavers build increase wetlands, reduce erosion and attract more wildlife. When a tree falls into Grenadier Pond (whether at the hands and teeth of a beaver or because the shallow roots of a non-native tree canít hold on to the sandy shore) lots of good things happen. Fish habitat is enlarged and improved. The increased sunlight encourages more aquatic plants, wildflowers and shore grasses. This removes sediment and pollutants from the water and attracts more insects, amphibians, reptiles and mammals. And BINGO! Our beaver is a habitat hero!
Youíve probably heard how busy beavers are. However, itís unlikely youíll get to witness their industrious feats because they are shy and they work at night. Beavers are impressively adapted to their aquatic responsibilities. In the water, its large leathery tail is both propeller and rudder. On shore, a beaver's tail gives support in both sitting and standing positions. To sound an alarm to fellow beavers, they slap their tails on the water. Their large webbed hind feet become powerful paddles for swimming. A clear membrane covers their eyes so they can see underwater, and before entering the water, special valves in their ears and nostrils close. The back of a beaverís mouth is built to prevent water from entering its lungs when it is carrying a mouthful of building supplies underwater. These features enable beavers to stay underwater for 15 minutes at a time! Beavers use their small dexterous front paws to arrange mud, stones and sticks for building dams and lodges. Perhaps their fur is the most important characteristic. It is extremely thick with long coarse outer hairs and fine short inner hairs that help the beaver survive in freezing water. After swimming underwater for quite some time, a beaverís skin remains dry.
Before Europeans arrived in Canada, itís estimated there were six million beavers in Canada. By the mid 1800s, nearly all of them had been killed for their fur. We are lucky to have them back right here in High Park.
Contributed by Kathleen Keefe