Polar bears need to put on about 180kg during their pregnancy, and the mother’s body will double in size. After that, though, she has one of the easiest labours. She digs a maternity den in a snowdrift, where she goes into a hibernation-like state called “winter sleep” and doesn’t eat for two months. (See a video of a mother polar bear and her cubs emerging from their hibernation at www.thetimes.com/youngtimes)
African elephants have the longest gestation period (how long it takes their unborn babies to grow) of any land animal — up to nearly two years — and give birth to the biggest babies on land, which weigh an average of 91kg. Doting elephant mums never allow their young ones to stray too far from their side. Mothers stay in touch with their offspring and enjoy close relationships with their daughters that can last for up to 50 years.
The longest pregnancy is that of the common frilled shark, at three and a half years.
Chickens turn their eggs up to five times an hour, while clucking softly to their unborn chicks, who chirp back to their mum and one another from inside their shells. Once they hatch, mothers use their wings to shield the chicks from predators. They may not leave their nests even during a fire if they have newly hatched young.
The female octopus lays more than 50,000 eggs at a time. It takes about 40 days for the eggs to develop and the mother stays close to them the whole time, protecting them from predators while gently blowing currents of water over them to provide oxygen. While she’s keeping watch over the eggs she can’t hunt for herself, so she may eat one of her own tentacles to keep herself alive.
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Female orang-utans spend nearly all their lives high in trees, where they build a new nest every night from branches and foliage, fashioning more than 30,000 homes in their lifetime. They never put their young down, nursing them until they reach the age of 6 or 7.
The largest bird eggs are those of the ostrich. They are about 18cm long, 14cm wide and weigh about 1.2kg. They are more than 2,000 times larger than the smallest bird egg — hummingbird eggs are 1.3cm long and weigh just half a gram.
Virginian and Yapok possums have the shortest gestation period, giving birth after just 12 days.
A mother giraffe often gives birth while standing, so the newborn’s first experience outside the womb is a 1.8m (6ft) drop. Baby giraffes can be more than 1.8m tall at birth.
Compiled by the zoologists at itvWILD. For exciting wildlife clips, facts and interactive games, go to itvwild.com