The walrus has a gestation period of about 15 months, including delayed implantation.
Walruses usually mate in winter, but the fertilized egg does not immediately implant in the uterus. This delayed implantation postpones embryo development for several months, helping synchronize births with favorable seasonal conditions. After implantation, active gestation lasts roughly 11 months, making the total reproductive period about 15 to 16 months.
Walrus calves are generally born in spring migration areas or on summer feeding grounds. A newborn calf is large compared with many other marine mammals and can swim soon after birth. Mothers typically nurse one calf and maintain a strong bond with it.
The timing is often misunderstood because “gestation” may refer either to the entire period from fertilization to birth or only to active embryonic development. Walruses are also notable for their long lives, large tusks, whiskers, and dependence on sea ice and shallow marine habitats.