With the lowest reproductive rate of all the pinnipeds, female walruses (Odobenus rosmarus) give birth just once every two or three years. Measuring in at 100 to 125 inches long and weighing between 1,300 and 3,300 pounds, they're hefty and sizable creatures. These aquatic mammals live in the Arctic, where they spend most of their time in the water, occasionally relaxing on ice or coastal beaches.
While cows become sexually mature between 5 and 7 years old, and bulls become sexually mature between 7 and 10 years old, they don't start to breed until they're roughly 10 and 15 years old, respectively. Breeding season occurs between the months of December and March each year, but not all of the cow walruses will be receptive come this time. Some will be pregnant and others will still be looking after calves born in previous years. Only those females who are in estrus will be looking for mates.
Finding a Mate
Groups of female walruses in estrus will break from the rest of their pack and gather on land, on rocky or sandy beaches, during breeding season. They need to be near the water, as this is where bulls make their calls and displays. Males stake out individual territories near these resting females and try to win their affection. These males can become aggressive with others of their sex during this time and will fight one another with their tusks. Bull walruses have series of different mating calls they use to attract females, including whistling and thumping noises they make underwater.
The Reproductive Act
Female walruses will mate with one only male during the breeding season, whereas the strongest males will mate with a number of females. Once cows have chosen whom they'll mate with, they'll join them in the water and dive together in a courting ritual. Walruses mate both in the water and on land, and may copulate several times to increase the chance of fertilization. Like other mammals, they mate using internal reproduction. Males have penile bones with which they extend their reproductive organs.
Pregnancy and Birth
Baby walruses are born between April and June, around 14 to 16 months after mating. Not all of this time is devoted to true gestation, as females are able to delay the implantation of the embryo for up to four months so their young are all born close together. Newborn walruses weigh around 130 pounds and are able to swim right away. They're not completely weaned until they reach 3 years of age.