Up close with a baby humpback 🐋 The mother is somewhere below while she lets the calf come up to breathe and interact with humans. A newborn calf is about 4.5 m long and can weigh 1.5 tons. Its mother’s milk is 35% fat and helps the calf gain around 45 kg per day during its first weeks of life. By 11 months of age, the calf can measure up to 9 m and will be ready to learn to feed itself.