Which Animals Have the Longest Gestation Period?

Long gestational periods in animals in usually linked to brain complexity and animal size.

Aug 12, 2023By Sara Payne
animals with long gestation periods

Humans have a long gestational period of 9 months. But did you know that some animals remain pregnant for over a year?

Animals, including the elephant, walrus, giraffe, sperm whale, and dolphin, have the longest gestational periods in the animal kingdom.

Why are these animals pregnant for so long?

What Affects a Gestational Period in Animals?

pregnant elephant and baby

Gestation is a term that refers to the time between when offspring is conceived to when it is born. This is the time when the fetus of the animal develops inside the uterus of the mammal. Mammals are unique in their development.

Most mammals are eutherian, which means they have a reproductive system similar to that in humans (Marsupials and monotremes are the outliers). Smaller animals tend to have smaller gestational periods. This is usually due to the size of the animal. It takes less time to develop a smaller animal in the womb.

Another factor involved in the length of gestational periods is food supply. Some mammals only breed during certain seasons. In this case, birth needs to occur when feeding supplies are at their most plentiful to help support the mother and her offspring.

In these cases, gestation keeps the baby in the womb longer as an adaptation. The long pregnancy ensures the baby is born at the best time of the year.

Male offspring typically gestate a few days more than females.

Scientists also suggest that animals that are more intelligent with more complex brains take a longer time to develop in utero, as well.


elephant pregnant

Elephants weigh between 4-6 tons and are 18-24 feet long when fully grown. These massive mammals are the largest land animals in the world. Females only have a calf every 4-5 years.

Males and females only get together when it is time to mate. Both sexes secrete chemicals that let the other know they are ready to mate.

After 22 months in the womb, the mother steps away from the herd to give birth. Calves can stand in a matter of minutes.

This long gestational period allows for a more advanced level of brain development. Although developing a more complex brain in the womb expends more energy and time, it is beneficial for highly social and intelligent elephants.

Their ability to recognize the complexities of their herd at birth helps them to survive better in their family structure, especially since they are animals that live mostly out in the open.



Walruses have a similar mating habit to that of elephants. Males and females live in separate herds and only meet up during mating season. Only the strongest males are allowed to mate. They fight each other for the right to mate.

Once mating has been successful, walruses have a remarkable trait. They have delayed implantation, which means the fertilized egg stops development. It hangs out in the uterus for 5 months.

This delay allows females to recover from their last pregnancy, nurse their current calf, and wait for better feeding conditions for their new offspring.

Walruses remain pregnant for 14 to 16 months before giving birth, but only about 11 months of that time is when the fetus is actively developing. Females care for their calves for about 18 months to 2 ½ years. They alternate years of pregnancy to allow them time to care for their young.


giraffe pregnant

The tallest land animals, giraffes, can stand 14-18 feet tall and weigh around 1,500 pounds. Their necks alone are 6 feet in length. It’s no wonder it takes a while for their young to develop in the womb.

Unlike many other large land mammals, giraffes can get pregnant while still nursing. However, there is usually a 19–20-month interval between pregnancies, on average. They also can get pregnant throughout the year rather than seasonally. This is probably influenced by food availability and rainfall.

Giraffes remain pregnant for 14 months. Calves are born with the mother standing up. They make a 5-foot drop, then can walk within hours.

Sperm Whale

sperm whale

Much like their large land mammal counterparts, sperm whales have a long gestational period.

Females remain pregnant for 14-16 months. This can vary between other whale species, but scientists believe this long gestational period has to do with both size and the migration habits of these animals. Mating occurs in tropical locations, and calves are typically born in cooler locations.

Sperm whales have complex brains with sonar capabilities. Females form tight bonds with their offspring and other members of their family unit, which they travel with.



Most species of dolphin have a gestational period of about 9-12 months. Their babies are born fins first (unique in marine mammals) to minimize their risk of drowning.

These remarkable marine mammals nurse their young for 2-3 years, teaching their offspring hunting and social skills.

Dolphins help support ocean life and are considered some of the most intelligent creatures on the planet. Their longer lifespan, complex brain, and social structure make their gestation period longer than other marine animals.


pregnant goat

Larger animals typically have longer gestational periods. However, long gestational periods can also be associated with complex brain structures, increased social tendencies in animals, delayed implantation, and availability of resources. Animals, especially mammals, have adapted in remarkable ways to increase their chances of future continuation.

Sara Payne
By Sara Payne

Sara is a mother of two and a high school English teacher who rediscovered her love of writing during the pandemic. She has 5 rescue cats: Neville and Luna, who are white cats with black and grey spots, and Ginny, Blue, and Fairy, who are calicos. Besides taking care of humans and fur babies, Sara enjoys gardening, crafting, and spending time in nature.