Life Cycle

As well as the age that they can breed and give birth, the reproductive history of female cetaceans can also be gauged from an analysis of their ovaries. With every egg produced, follicles erupt in the ovaries, and instead of disappearing like they do in most mammals, they remain for the rest of the animal's life. By counting these follicles it is possible to determine at least how many times a female as ovulated (though not the number of times this has resulted in a pregnancy).

Sexual maturity

It is believed that cetaceans reach sexual maturity before they reach physical maturity. Female bottlenose dolphins can become sexually mature as young as 5 years old, although most don't become mature until their 'teens' at around 11 or 12. There may be problems during the pregnancy if they conceive when they are too young and not fully-grown. An older female will be more experienced and this should benefit her calf. Males become sexually mature between the ages of about 8 and 13 years old. For information on each species in the Delphinadae family please click here to go to information by species.

Breeding Seasons & Cycles

The timing and length of the reproductive cycle depends on both biological factors; such as the frequency of ovulation, the gestation period, and the age at which the young are weaned together with environmental factors; such as the availability of food for both the pregnant or nursing mother and her new born. For information on each species in the Delphinadae family please click here to go to information by species.

Courtship & Mating 

When it is difficult even to identify the age or sex of cetaceans, the task of recognizing sexually related behaviour is extremely hard. In many ways cetaceans are no different to any other animal; in order to mate sexually mature adults must be able to find each other, confirm a readiness to breed and then obtain the opportunity to mate. Fluke slapping, high speed chases, nuzzling and body rubbing could all be part of courtship behaviour. In bottlenose dolphins such courtship behaviour, if successful, is followed by the male swimming beneath the female and mating with her, with their bodies at right angles to each other. As in many mammals, mating is swift, lasting only a few seconds, but is often repeated. Dolphins don't stay with the same partner for life and, in fact, males don't appear to play any part in helping to raise calves. Dolphins are promiscuous animals and spend a lot of their time in sexual play with almost any other member of the group.

Pregnancy & Birth

After fertilization the female's pregnancy is similar to that of other mammals. Bottlenose dolphins' gestation period (the length of time that they are pregnant) is about 11 or 12 months. Cetaceans are unusual in that the size of their offspring at birth is not determined by variations in the length of the pregnancy, but by the differential rate of foetal growth.

Bottlenose dolphins are quite slow breeders and females usually only have a calf every three to five years. They also give birth to just one baby at a time; dolphin twins are very, very rare, and sadly normally die either before birth or soon after being born. The mother will not have any more calves until she has weaned the first one.

When the time comes to actually have the baby, a mother may move into certain areas, away from all the normal noisy goings-on. The initial stages of birth may be quite slow, with the flukes of the partly emerged offspring protruding for an hour or more. But once the final stage has been reached the young emerge rapidly usually within 20 to 30 minutes. This is essential as once the umbilical cord is ruptured the calf must be quickly transported to the surface to take its first breath. A dolphin calf is born tail-first with eyes open, senses alert and enough muscular coordination to follow its mother immediately. Cetaceans typically give birth near the surface. The lack of oxygen in the lungs of the young cetacean together with the lack of blubber means that they are not buoyant, they sink rather than float and as a result the mother, and sometimes attendant 'midwives' immediately nudge the newborn to the surface for its first breath.

Soon after birth the calf is fed by the mother near to the surface so that it can breathe regularly. When suckling, the young approach from the rear. The mother will often turn to her side, to aid the youngster in finding the nipple. Because cetaceans do not have lips, the calf cannot suckle in the same way as terrestrial mammals. Instead, the calf grips the mother's now protruding nipple between its tongue and the roof of its mouth to make what it is believed a "tube". This makes the feeding process faster, which is necessary as the young cannot suckle for long periods due to the necessity to breathe. For the first six months or so, a calf will feed on its mother's milk. Cetacean milk is creamy white in colour, and may be tinted pink. It contains an unusually high percentage of fat; 15 -50 percent fat, compared with 3-5 percent in cow’s milk and a low sugar content. This may be due to the fact that the animal must develop quite quickly. A blue whale doubles its birth weight in only 7 days, while a cow may take 50. Then the youngster will start adding fish to its diet, which it may even start catching itself. As it gets better at catching its own food, the calf needs less milk and becomes a little less dependent on its mum.

On average  bottlenose dolphin calves measure between 0.85-1.3 metres (33-51 inches) at birth and weigh between 15 and 30 kg (33 to 66 pounds) For information on each species in the Delphinadae family please click here . New-born calves are generally much paler than adults and have creases known as 'foetal folds' down their sides, probably from having been squashed up in the mother's womb. The calf is so dependent on its mum that the two must stick together like glue. When a calf is first born, its mother will whistle over and over again. The calf will learn her whistle and always be able to find her, even amongst lots of other mothers and calves. Dolphin milk is extremely rich and fatty compared to human milk or cow’s milk. Mothers nurse their young about four times per hour during the first week of life, and gradually reduce nursing frequency thereafter.

Whales, dolphins and porpoises are born already able to swim, with fully formed vision and hearing. However, the babies are small and a bit wrinkly, and they are vulnerable. At birth the mother, or fellow pod member, will immediately help the newborn to the surface to take their first breath of air. It takes the baby a few days to master surfacing smoothly for air at his or her mother’s side; at first they are a little clumsy and tend to push their heads too far out of the water. By the end of two weeks, infants are fairly coordinated and can begin taking deeper dives. They stay close to their mums; and all mothers protect their babies from predators.

Young whales and dolphins need ongoing guidance and support from their mothers as they learn life skills and the cultural ways of their population and species. For many whales and dolphins, mothers and youngsters continue to stay close together long after the important early-life connection period. Family associations among whales and dolphins vary in terms of the kind or degree of closeness and the longevity of the relationships. The bond may be loose and temporary or it may be lifelong.

Although the young toothed whales typically nurse for longer, all cetacean young begin to feed themselves at the age of a year or so. The young are born without teeth or baleen but these usually appear within a few months. While nursing lasts between 1.5 to 2 years, the mother will remain with her calf for a period between 3 and 8 years.

Juveniles

In general, juvenile bottlenose dolphins of both sexes will leave their maternal group somewhere between the ages of 3 and 6. They form their own groups and properly fend for themselves for the first time, this is a difficult period for young dolphins, but this juvenile period appears to be critical for developing both skills and relationships necessary for survival and reproduction. They stay in these groups until they become sexually mature.

Life-span

It is difficult to accurately determine the lifespan of cetaceans as many of them have ended artificially by being harpooned or caught in nets.  Life expectancy is determined by many factors such as its habitat, geography, diet, lifestyle, level of endangerment, and species. Baleen whales can live over 100 years; blue whales may live  70 to 90 years on average, fin whales may live 60 to 100 years, Sei whales may live as long as 60 years and the average lifespan for a bowhead whale is 100 - 200 years. For the toothed whales, the life expectancy also  varies by species but ranges from 10-20  years for Atlantic spotted dolphins to 90 years for killer whales (although the average is about 50 years).  Female bottlenose dolphins, on the whole, live longer than males. Females have been recorded at over 50 years of age in the wild whereas males usually don't live much over 45.

An interesting fact, however, is that some female cetaceans often live beyond the menopause. Although this is common in elephants and humans, this is a relatively rare occurrence in the animal kingdom as there is little obvious value to a species for its members to live beyond the point that they can produce offspring.

For information on each species in the Delphinadae family please click here to go information by species.

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Scholarly links

For more information on this topic please explore these scholarly articles noted below:

• Age estimation

• Pregnancy and Fetal Development: Cephalic Presentation and Other Descriptive Ultrasonographic Findings from Clinically Healthy Bottlenose Dolphins (Tursiops truncatus) under Human Care

• Ultrasonographic findings associated with normal pregnancy and fetal well-being in the bottlenose dolphin

• The life history of free-ranging Atlantic Spotted Dolphins (Stenella Frontalis): age classes, color phases, and female reproduction