Rabbits and muskrats are also frequent producers. Humans, some farm animals, and a number of other placentals typically give birth to just one offspring each year. The black bear may breed once every two years and deliver only one or two cubs weighing under one pound each at birth. Water is home to many mothers of nature. Otters, muskrats and beavers are natural swimmers who prefer to live in homes built on or near rivers, ponds, lakes, and streams.
Otters have a special reproductive system common in the mustelidae family.
It may be up to one year from the time they breed until the young are born. The fertilized egg does not implant into the wall of the uterus to continue development for months after breeding takes place. This is known as delayed implantation. Hair or fur is a feature in every mammal, even marine mammals like whales and seals. Then there is the porcupine.