Birthing a Baby Dolphin
What could be more adorable than a baby dolphin? Granted, they lack the fuzzy cuddly look that we all love they make up for it with their diminutive size and ready-to-go, rock-and-roll attitude. These little swimming footballs charm us as they bow ride with their mothers born fully equipped to swim, breathe, and keep up with the pod. The lives of the babies (referred to as ‘calves’) depend upon some fairly unique mechanisms.
Although there are some variations, most of the small to medium sized dolphins have a calf every 2 to 3 years. Although there are seasonal peaks in late spring and late autumn, babies are born year round. The gestation lasts 10 to 12 months, and the fetus develops so that the mother stays streamlined. This amazing adaptation also allows the calves to be born almost invariably tail first because the highest point of the uterus leads towards the birth canal. Because the tail end of the fetus is lighter than the head end, it rises to the higher side. The flukes and flippers are folded up, permitting the calf to be born tail first.
After a short labor (usually 2 hours or less of active labor), the calf is born, and the next adaptation kicks in – their umbilical cord is equipped with a special breakaway spot that breaks as soon as the birth is complete. Instinctively, the calf immediately swims to the surface to take its first breath. Mother and usually another female dolphin are close by to help with the process. The rest of the pod usually forms a protective circle around them. If a shark approaches a female with a calf, it will be chased off by a group of males.
Dolphin’s milk is incredibly rich, high in fat (around 22%, compared to 3.6% for cow’s milk), high in protein, and low in sugar. The actual content of the milk changes over time, as the young dolphin takes more of its nutrition from fish, and weaning occurs. The thick, creamy milk is more or less injected into the throat of the calf – another wonderful adaptation to the aquatic environment. The mother’s mammary glands are inside two slits, which again keeps her streamlined for swimming, and it is thought that the calves form a tube with their tongue and the roof of their mouth. They tap their mother’s mammary slit with their rostrum, which cues her to eject the milk, and in under 10 seconds the baby gets a meal! This is one of the adaptations that allow the pair to keep up with their pod – they don’t need to stop for long nursing bouts.
Another adaptation that allows for the young dolphins to keep up is the way they hitch a ride in their mothers’ slipstream. What that means is that as the mother dolphin swims along at high speed, two things happen. First, the pressure drops next to her, which acts kind of like a magnet to draw the calf close (for the scientifically minded reader, this is ‘ Bernoulli suction’), and second, the water behind the mother pushes forward to replace the water she pushed out of the way. The calf saves 60% to 90% of the effort to keep up with her, at speeds up to 2.4 m/sec. This translates to slightly less than 4 knots – about the same speed that the spinner dolphins tend to bow ride off the tour boats.
This synchrony and coordination with the mother is therefore essential for the survival of the calf, and continues for as long as four years. Starting about the second month, the calves begin to forage on their own a bit, and even though they feed more and more independently, their ability to breathe in synchrony with their mother actually increases over time.
Weaning takes place gradually, with no visible effort from the mother. Scientists have not ruled out the possibility that the females use subtle cues or sound to discourage the calves, or the milk quality declines significantly, but it is theorized that the young dolphins just begin to devote more of their time to social interactions with other young dolphins. The calves of similar age play together, usually circled by adults, and practice leaps and bursts of speed. They (as well as juveniles and adults) will find bits of seaweed and drag it along on their flippers, flukes or rostrum, often passing it back and forth. Fish make convenient toys, and they will mock chase them, and have been known to release the fish unharmed after they catch them. If the youngsters get too out of line, the adults will discipline them by snapping their jaws, pushing them with their rostrums, slapping them with their tails, biting, or holding them at the bottom.
Once weaning is complete, the males will associate in all male groups, becoming mature around 10 to 12 years old. The females tend to align with older females and often take on the role of helper to a pregnant or nursing female. The females mature earlier than the males, between 5 and 10 years, when they will breed and become mothers themselves. And so the cycle continues.
Aquatic Mammals 2003, 29.3, 363–377
Underwater analysis of the behavioural development of free-ranging Atlantic spotted dolphin (Stenella frontalis) calves (birth to 4 years of age)
Jessica A. Miles1,2 and Denise L. Herzing1,2
Journal of Ichthyology and Aquatic Biology
Rest, nurture, sex, release, and play: diurnal underwater behavior of thespinner dolphin at Fernando de Noronha Archipelago, SW Atlantic
José Martins Silva-Jr1,2, Flávio J. L. Silva1,3 and Ivan Sazima4
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