Walruses are large marine mammals recognized by their prominent tusks, inhabiting Arctic and subarctic regions. These social animals live in shallow, food-rich waters, often hauling out onto ice floes or land for rest and reproduction. Understanding their reproductive habits, including offspring numbers and subsequent care, offers insight into their life cycle in their challenging environment.
Walrus Birthing Patterns
Walruses almost exclusively give birth to a single calf; twin births are exceedingly rare, though such instances have been documented. Female walruses typically reproduce every two to three years. This extended interval is due to their long gestation period and prolonged calf rearing.
Births generally occur during the spring migration, from mid-April to mid-June. Calves are usually born on stable ice floes, providing a platform for birthing and early care. On these ice platforms, females with young often gather in “nursery herds,” ranging from 20 to 200 individuals. Sea ice is crucial for walrus birthing and nursing.
Gestation and Calf Development
Walruses have a long gestation period, approximately 15 to 16 months. This extended pregnancy includes delayed implantation, where the fertilized egg remains free-floating in the uterus for several months before implanting. This strategy helps ensure calves are born during favorable spring conditions.
Newborn walrus calves, often called pups, weigh between 45 to 75 kilograms (99-165 pounds) and measure about 95 to 123 centimeters (3-4 feet) long. They are born with dense, short fur that is ashen gray to brown, which changes to a reddish-brown or tawny color within a couple of weeks. Unlike adults, newborn calves do not have tusks; these begin to emerge from the gums around six months of age. Calves can swim shortly after birth, though they remain close to their mothers for nursing.
Maternal Care and Calf Rearing
Walrus calves are highly dependent on their mothers for an extended period, forming one of the longest and strongest mother-offspring bonds in pinnipeds. Calves remain with their mothers for at least two years, sometimes up to five years, learning survival skills. This prolonged maternal investment results from the calves’ slow growth rate and their need for extensive instruction in foraging and navigating their Arctic environment.
Mothers provide continuous nursing, often in the water, though calves can also nurse when hauled out on ice or land. Walrus milk is rich in fat and protein, supporting the rapid growth of the calf, which can gain 0.7 to 0.9 kilograms (1.5-2 pounds) per day. Mothers are protective, defending their young from predators like polar bears and killer whales. They teach their calves to locate food using sensitive whiskers, navigate ice floes, and avoid dangers. This ensures the calf’s development until weaning and eventual separation.