Narwhals typically have only one calf per gestational period, and typical gestational periods last around 16 months, according to Defenders of Wildlife. Calves nurse for at least a year and stay with their mothers for up to 20 months.

Narwhal females give birth every three years throughout their reproductive life, which starts at 4 to 7 years old. At birth, calves measure around five feet long, and by adulthood they can reach up to 16 feet. Narwhals weigh around 180 pounds as newborns, but can grow to weigh up to 1.8 tons. Females tend to be smaller than males, and males reach sexual maturity later, usually between 8 and 9 years old.