Sea lions and fur seals belong to the family Otariidae.
They have ear flaps and can rotate their hind flippers forward, giving them a somewhat ungainly, but very agile, gait on land. These are the "circus seals"—the ones seen in circuses and aquaria—able to stand on their fore flippers and climb stairs.
In the water, sea lions and fur seals use their fore flippers to propel themselves, with a wing-like flying motion, using their hind flippers to steer (the exact opposite of true seals).
A female sea lion or fur seal gives birth to one pup each year. She will nurse her pup for a few days and then depart to sea to feed, leaving the pup in a nursery group or a protected area for three to five days.
Upon her return, she will call the pup, using a distinctive bark that the pup will answer. Mothers and pups recognize each other through sound and smell—this bond is very strong, and a female can pick her own pup out of dozens of others.
The mother will continue this cycle of feeding and nursing for several weeks until the pup is old enough to swim and keep up with her. She will then depart to sea, taking the pup with her, to teach it to swim, feed, and avoid predators. The pup will be weaned in a year, when the mother comes to shore to give birth to her next pup.
Male sea lions and fur seals compete fiercely for access to females or to the territory females prefer. This leads to pronounced sexual dimorphism—that is, males are much larger (in some cases, five times heavier) than the females and have secondary sexual characteristics such as thick necks, manes, or large canine teeth.
Males generally mate with females during the first week of nursing. The embryo will begin to develop, but then remain suspended in the womb (this is called delayed implantation), until a female has rebuilt her blubber stores.
