Dolphins are incredible, intelligent animals - more intelligent than chimpanzees, according to some scientists. They are also mammals, which means they must give birth to immature, helpless calves and nurse them until they can fend for themselves. The mammals of the sea might seem very different from us, but the differences are not so huge when you look closely at the ways they look after their young.
A few weeks ago I wrote about dolphins' births, and how they are sometimes attended and assisted by close relatives of the mother. In this post I am looking at how dolphins nurse and carry their young.
Dolphins breastfeed their babies for around two to three years. The mother usually weans her calf when she is pregnant with a subsequent baby, but a calf has been observed nursing up to the age of ten. Like other intelligent mammals, the mother-baby bond seems to be very important and mothers only leave their calves when they need to find food. Even when they are apart, they use sound and echo-location to remain in touch.
Dolphins do not have protruding mammary glands like primates, but evolution has found a way for them to breastfeed and remain streamlined in the water. The mother's nipples are hidden within slits on her belly. A baby dolphin must locate the nipples and latch on with its mouth, forming a tight seal that prevents any salt water from mixing with the milk. Dolphins obviously need to go to the surface to breathe, so a mother helps her newborn baby by lying on her side near the surface so that the calf can feed safely, close to an air supply. As the calf gets older, it is able to find the nipple without such assistance.
The act of releasing the milk, which we call let-down in humans, is under the voluntary control of the mother dolphin. The milk is richer and fattier then human milk, meaning that dolphin calves do not need to spend as much time feeding as human babies. Newborn calves feed around four times per hour but each session lasts for a matter of seconds rather than minutes.
Infant carrying is seen in all land-dwelling primates, and ocean-dwelling manatees and sea-otters also physically carry their young in the water. So it is no surprise that dolphins have evolved a method of "carrying" their offspring. When the babies are very young, the mother-calf pairs swim in "echelon" position with the young dolphin by its mother's side. It is thought that the flow of water around the pair's body creates pressure that keeps the infant close to its mother and helps to propel it along in the water. Older calves swim in "infant" position below their mothers where they have better access to the nipples and are possibly given more protection from predators.
I think it's astounding how many similarities there are between the ways dolphins care for their young and what we humans do. As I wrote last time, we both have assistants attending childbirth (at least some of the time) and, if we are behaving as biology intends, we nurse our babies for similar lengths of time. For the majority of the global population, baby carrying is the normal method to transport a human infant. And though they do not have arms and legs, dolphins also have a way to carry their young. Most importantly, we both form close mother-infant bonds that last many years before a youngster is ready to leave the care of its immediate family.
Although we walk on land and dolphins swim in the sea, there are clearly many behaviours that bind us together.