You should have a pretty good idea of what your species needs in its environment to be healthy and vibrant. Do you know if your watershed is healthy for your species?
All mammals reproduce sexually—sperm from the male fertilizes the female's egg—and the female gives birth to live young. Both beaver and river otter females reach sexual maturity at about three years of age. Male otters have multiple female mates, whereas beavers stay with the same mate for life. Beavers tend to have larger litters of babies or kits; otters usually just have one offspring at a time. Both young are able to swim at birth. The female will nurse and care for the young for 1-2 years before they're old enough to go off on their own. The average lifespan of these mammals is 15-20 years.
Otters are carnivores, living on fish, amphibians, aquatic reptiles and invertebrates and often taking the role of top predator in freshwater ecosystems. Beavers, on the other hand, are herbivores, eating mostly leaves, roots, bark and twigs. Beavers are especially fond of cambium - the soft tissue that grows under the bark of a tree.
Beavers play a very important role in the energy web as a keystone species. This means their presence in nature greatly affects other wildlife. Beavers build dams and create wetlands upon which many species depend. Almost half of all endangered and threatened species in North America rely on wetlands to survive, and eighty-five percent of all North American wild animal species depend on wetlands. Beaver dams also help purify and control water by filtering silt from the water bodies. They can also slow flood waters and aid in containing forest fires. Beavers can serve as "ecological indicators." Their presence in an area lets us know the ecosystem is healthy.
Both otters and beavers are semiaquatic, spending much of their time in the water. Otters can thrive in any water habitat, such as ponds, marshes, lakes, rivers, and estuaries—and in cold, warm, or even high-elevation areas—as long as the habitat provides adequate food. Beavers, however, live exclusively in freshwater habitats. Both mammals build their shelters (called dens for otters, lodges for beavers) along waterways with the entrance underwater.