Mothers spend a lot of time teaching them survival and behaviour skills, building up their strength and stamina for the long migration south to the summer feeding grounds in October. Calves are 4-5 metres long at birth and weigh about 1 tonne. Needing to gain up to 10 tonnes in weight and 8 metres in length during the first few months, they consume up to 125 litres of very rich mother's milk and put on about 90kg in weight daily. They grow to about 10 metres in their first year, by which time they are weaned from and independent of their mothers. A natural feature of southern right whales are the thick, callous type skin growths around their heads called callosities .
Whales also grow some sparse hair, usually on the front of the lower jaw.
Southern rights are usually black, but some white calves are born but darken as they get older, going through stages of grey to brown then black. They may have irregular white patches on the abdomen and chin, which are also useful for identification. Southern rights are the only great whales that do not have a dorsal fin on their back, neither do they have throat grooves like other baleen whales such as humpbacks and blues. All whales are mammals, not fish, and breathe air through the nostrils or blowholes on top of their heads. Being baleen whales, southern rights have two blowholes, which gives them a distinctive v-shaped bushy blow.