How do whales mate?
Like other mammals, such as humans, male whales have a penis and females a vagina. They mate underwater, usually belly to belly, while either stationary or swimming.
Males may mate with more than one female, and females with more than one male.
Rate of birth
Like most other large animals, whales have a low birth rate. On average, they become sexually mature around 8–10 years old, and a cow may give birth to one calf every few years.
A sexually mature female whale generally spends one year pregnant and six months nursing her calf. She then rests for a further six months before attempting to mate again.
Pregnancy and birth
Whale calves normally take about 10–12 months to develop in the womb. Although multiple foetuses have been found in pregnant females, it is rare that more than one is born at full term.
The calf is born tail first – and ready to swim! This is an essential ability, as it has to get to the surface to breathe. The newborn calf is already well developed – it may be as much as a third of the length of the mother. The dorsal fin and tail flukes are quite floppy, but stiffen within a few days.
Feeding the infant
In humans, the baby latches onto the mother’s nipple to suck milk. In whales, the calf places its mouth on the mother’s nipple and she forces out the milk into the calf’s mouth.
Mothers nurse their calf for at least four months, and for much longer in strongly social species (mostly the toothed whales). In these groups, calves may drink milk from other females while their mother dives for food.
In less social species (mostly baleen whales), the mother will tend to dive less deeply so the dependent calf will not be left alone for long.
Whale milk has a fat content ranging from 16–46 per cent. Human’s and cow’s milk ranges between 3–5 per cent. Whale calves grow fast on their rich food.
Weaning is a gradual process, with the young animal starting on solid food before it has finished with its mother’s milk – just as humans do. The weaning period for baleen whales is much shorter than for toothed whales.