Beavers: Lords of the rivers

A beaver will only fell a tree for a particular reason - be it a larger mature tree to form a dam, or a young tree for food. They are herbivores and eat mainly leaves, bark and twigs, as well as aquatic plants. A single beaver needs just five minutes to fell an 8-foot (2.4-meter) tree.

Beavers have their own kind of swimming goggles, in the form of a set of transparent eyelids that enable them to see underwater. There are two species of beaver: the European beaver and the North American beaver. Although they look and behave similarly, they are not genetically compatible.

Beavers use their broad tails like rudders to steer underwater, and can swim at speeds of up to 5 miles per hour (8 kilometers per hour). They also use their tails to slap the water as a warning of danger, or as a warning signal to alert others to keep away. Beavers can remain underwater for 15 minutes without surfacing.

Beaver homes are called lodges, and are built in the form of domes made of branches and mud. They are located in open water for protection from predators, and have underwater entrance holes. Beavers are active throughout winter and use their ponds even when they are covered with ice.

Beaver lodges usually contain two dens, one for drying off after entering the lodge underwater, along with a second, dryer den where the family will live and socialize. There are usually between two and 12 beavers in a colony, and three baby beavers, or kits, born per litter to a beaver couple each year.

Beavers create their dams - large log, branch, and mud structures - to block streams, turning fields and forests into the large ponds they love. Beaver dams can be vast - the largest is in Wood Buffalo National Park, Alberta, Canada - it stretches for 850 meters, and is visible from space.

It is this ability to transform the landscape that causes particularly farmers to consider them as pests: beaver dams can cause floods and block irrigation. They also fell trees that humans might want to leave standing. But beavers play an important role in ecosystems, helping to regulate water flows and humidifying the land.