Animals With the Longest Pregnancies: Elephants and Beyond

How long is the longest pregnancy?

Pregnancy, or gestation, is the time between conception and birth. In mammals it ranges from under two weeks to almost two years, and the record belongs to elephants. The African bush elephant carries its single calf for about 22 months, roughly 640–660 days, and the Asian elephant for about 18–22 months, usually near the upper end. For the full story of elephant pregnancy, see how long are elephants pregnant?

Gestation lengths are averages. They vary between individuals, are best known from zoo animals, whose pregnancies can be timed exactly, and for wild whales are often estimated from the sizes of unborn calves found during the whaling era.

Why do some animals have such long pregnancies?

Several factors work together. Large mammals generally have slower metabolisms and longer gestations than small ones, so a mouse is pregnant for about three weeks and an elephant for nearly two years. The state of the newborn matters too. Animals whose young must walk, run or swim almost at once, such as elephants, giraffes, rhinos and whales, give birth to large, well-developed babies after long pregnancies, while animals with helpless newborns, such as bears, cats and marsupials, have short ones.

Brain growth adds time, because nervous tissue develops slowly. Finally, many species time birth to the season: a pregnancy that lasts about a year, or a little more with a pause, lets young arrive when food is most plentiful.

1. Elephants: about 22 months

Elephant calves are born big and well developed, weighing around 90–120 kg (200–265 lb). They can stand within an hour or so and must keep up with a herd that walks many kilometers a day, so a long pregnancy gives them time to grow a large, complex brain and a strong body. A newborn elephant’s brain is already about a third of its adult weight.

Because pregnancy is so long and calves suckle for years, a female usually gives birth only every four to five years. That slow breeding is one reason elephant populations recover so slowly from poaching.

2. Rhinoceroses: 15–16 months

Rhinos have the next-longest pregnancies among land mammals. The white rhino is pregnant for about 16 months, the greater one-horned rhino of India and Nepal for about 15.7 months, and the black rhino for about 15 months. The calf is born weighing roughly 35–65 kg (75–145 lb), depending on the species, and can follow its mother within hours.

3. Sperm whale and orca: up to 18 months

Some toothed whales have very long pregnancies. The sperm whale carries its calf for about 14–16 months, and females give birth only once every several years, which makes them one of the slowest-breeding mammals. Orcas, or killer whales, are pregnant for about 15–18 months. In the Arctic, narwhals carry their young for about 14–15 months and belugas for roughly 12–14.5 months.

Size alone does not explain this. The blue whale, the largest animal that has ever lived, is pregnant for only about 10–12 months. Many baleen whales time their pregnancies to fit a yearly cycle of migration between polar feeding grounds and warm breeding waters.

4. Giraffe and okapi: around 15 months

A giraffe is pregnant for about 400–460 days, roughly 13–15 months. Mothers give birth standing up, so the calf drops about 1.5–2 m (5–6.5 ft) to the ground, and it can usually stand and walk within an hour. Its close relative the okapi, a shy forest animal of the Democratic Republic of the Congo, has a similar pregnancy of about 440–450 days.

5. Walrus: 15–16 months, with a pause

The walrus is pregnant for about 15–16 months, but for the first three to four months the embryo does not develop. It floats in the womb as a tiny ball of cells before attaching to the uterus wall, a pause called delayed implantation. This lets walruses mate in winter but give birth the following spring, when conditions are best for the calf.

6. Other mammals that are pregnant for over a year

• Camels: dromedaries and Bactrian camels carry their calves for about 13 months, sometimes longer.
• Tapirs: the Malayan tapir is pregnant for about 390–395 days.
• Manatees and dugongs: manatees for about 12–14 months, dugongs for 13–15 months.
• Bowhead whale: about 13–14 months.
• Donkey: about 12 months, often a little longer.

Horses, by comparison, are pregnant for about 11 months, around 340 days on average.

Delayed implantation: pregnancies with a pause

Several mammals stretch their pregnancies with a pause like the walrus’s. The European roe deer mates in July and August, but the embryo stops developing until about midwinter, and fawns are born the following May or June, after about 10 months. Brown bears mate in late spring and early summer, yet the embryo floats free for months and only implants in autumn, so cubs are born in the winter den. In these animals, the total time from mating to birth says little about how long the baby actually grows.

Record carriers beyond mammals

Some of the longest pregnancies in the animal kingdom belong to animals that are not mammals:

• Frilled shark: this eel-like deep-sea shark gives birth to live young, and a study of embryos in Japan estimated that its pregnancy may last up to about 3.5 years. If correct, that is the longest of any vertebrate, but it has never been directly observed.
• Alpine salamander: this black salamander of the European Alps gives birth to one or two fully formed young. Pregnancy usually lasts about two years at 650–1,000 m (2,100–3,300 ft) above sea level and about three years at 1,400–1,700 m (4,600–5,600 ft), with a range of two to four years.
• Spiny dogfish: this small shark of cool coastal seas, common off Europe and North America, carries its pups for about 18–24 months.
• Basking shark: pregnancy is thought to last more than a year, perhaps two to three, but only one pregnant female has ever been examined.

Egg-brooding animals can be just as patient. A deep-sea octopus, Graneledone boreopacifica, was watched guarding her eggs in Monterey Canyon, off California, for 53 months, about four and a half years, the longest brooding period known for any animal.

The shortest pregnancies

At the other extreme, marsupials have very short pregnancies and finish raising their young in a pouch. The Virginia opossum, North America’s only marsupial, is pregnant for just 11–13 days, and its newborns are about the size of a honeybee. Many small rodents are pregnant for about three weeks.

How does a human pregnancy compare?

A human pregnancy lasts about 40 weeks, roughly 9 months, counted from the start of the last menstrual period, or about 38 weeks from conception. That is long for a mammal of our size, partly because human babies grow large brains before birth, but it is less than half an elephant’s.

Longest pregnancies compared