Walruses are capable of holding down seals and small whales with their flippers and tearing them apart with their tusks. In the winter, when accompanying the females and young, the bulls apparently eat very little. Because walruses breed during the harsh Arctic winters, little is known about their mating systems. The walrus mating system is believed to be a female-defense polygyny. Large mature males have exclusive access to a herd of females for 1-5 days at a time.
Courtship behavior is described in the next section.
Mating takes place in January and February, most likely underwater. Walruses are interesting because implantation of the blastocyst is delayed for 4 or 5 months, until June or July. Females give birth to a single, precocial offspring. The calf is about 113 cm long and weighs approximately 63 kg. It is grey in color and can swim at birth.