Blue whale calves are born after gestation periods of 10 to 12 months. They nurse for 6 to 7 months, and the total calving period is 2 to 3 years. Blue whales reach sexual maturity at 5 to 15 years of age. The exact lifespan is not known, but by counting the layers of a dead whale's earplugs, scientists estimated that one blue whale specimen reached the age of 110.
Blue whale calves weigh up to 3 tons at birth and are up to 25 feet long. The mother's rich milk is 35 to 50 percent milk fat, and baby whales consume about 50 gallons a day, gaining weight at the rate of up to 10 pounds an hour or 250 pounds a day. By the time the calf is weaned, it is over 50 feet in length.
Female blue whales are usually larger than males. In the northern hemisphere, when they reach sexual maturity, males are 66 to 69 feet in length, and females are 69 to 75 feet long. Both genders are slightly larger in the southern hemisphere. They mate from late autumn to the close of winter. Blue whales generally travel alone or in pairs, although in areas where food is abundant, many can be seen in close proximity to each other.