Beavers are herbivores (vegetarians/plant-eaters). [86] They have a specialized digestive system. Colonies of microorganisms in their intestines digest up to 30% of the cellulose from the tree bark and other woody material they eat. Further nutrients are recovered in the form of fecal pellets that the beaver will re-ingest. [87] Beavers will eat bark from hardwood trees such as birch, aspen, willow, cottonwood, and adler. They will also eat leaves, roots, and twigs from certain trees such as willow and aspen, and water plants of all kinds, along with grasses, and buds. [88]  [89] Beavers don't actually eat wood, only the cambium, a soft tissue close to the surface in which new wood and bark grow. [90] Some of their favorite foods include water lily tubers, clover, apples, leaves, and cambium from Aspen or other fast-growing trees. [91] Most of their favorite herbaceous foods are only available in summer. During winter, their diet consists mainly of woody material such as shrubs, saplings, and branches that are planted underwater in the mud close to the lodge entrance. The beavers will feed on this underwater cache of edible branches all winter since they cannot break through the ice to cut fresh branches. And there would be no new growth such as buds or shoots if they did. [92] When a beaver fells a tree, they will first eat the bark and buds off, and then cut up branches and any sections of the trunk that they can carry for use in their dams or lodges. [93] They have five clawed dexterous digits on their front feet to manipulate food. [94] The available food supply close to their home waters is the determining factor that governs a beaver colony. As the food supply is used up in an area, longer trips increase the beaver's expose to predators, and the time it takes to reach the food source from home. When an area's food supply has been exhausted, the family must migrate to a new home. [95]

Close-up of a beaver.
Close-up of a beaver.
Image Source: NPS Photo by Condon

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Beavers are monogamous and mate for life. However, if their mate dies they will usually find another. [96] As with other species, offspring from a previous litter may be rejected by a new male. [97] Males do not fight over females, but when the family unit has been established both sexes tend to be very territorial. Scent mounds mark their territory and let other beavers know that the area is occupied. [98] Mating takes place in January or February, and 1 to 9 (usually 4) kits are born in late April to June after a gestation of 105 days. [99]  [100] The nutrition the mother receives from her food and her general health help determine the number of kits born. [101]  Before the birth, the female makes a soft bed in the upper room of the lodge for the kits. [102]

Image Source: NPS Photo

At birth the eyes of the baby beavers are open. They are covered with soft fur, and they weigh about 1 pound (.45 kg). They will begin to swim in half an hour. In about a month they will be able to hold their breath and swim underwater. [103] [104]  [105] When the kits tire, the mother beaver will carry them on her back. [106] A kit is weaned at about two weeks. [107] Both parents care for the kit, and even the previous year's young will sometimes help in this work. [108]  [109] Young beavers reach adulthood in their second winter. When spring comes, they will move away to find a mate and build a lodge of their own. [110] As noted earlier, the health of the female will determine the size of each litter. This mechanism self regulates the beavers reproduction rate. As a result, beaver populations in an area will naturally peak and then slowly decrease to a sustainable level. [111]

Written by Samuel Fall
Copyright © 2007 Beaver Pictures & Facts

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Image Source for beaver lodge at top of page: M. LeFever, U.S. Fish and Wildlife Service.
Image Source for two beaver at bottom of page: Tom Smylie, U.S. Fish and Wildlife Service.