Giving birth to the next generation can be an extreme event for mothers (and, if you're a sea horse, fathers) in the animal kingdom.
In appreciation of all the mothers out there on Mother's Day, Live Science has compiled a list of the eight most extreme animal births. Read on to see cute animal babies, and to gain a new respect for the mothers who went through great feats to bring their children into this world.
Naked mole rats
Naked mole rats (Heterocephalus glaber) are incredibly social mammals that live in colonies. But each colony has just one reproductive female: the queen.
She isn't part of a family line, however. Rather, if another female wants to become queen, "she has to go up to the current queen and kill her," said Kenton Kerns, the assistant curator of small mammals at Smithsonian's National Zoo in Washington, D.C.
Once she becomes queen, the matriarch starts having babies, usually about 10 to 15 at a time, which is fairly similar to the number of pups birthed by other rodents, such as mice or rats. However, the number of the litter grows over time. That's because naked mole rats are the only mammals whose bones grow after they reach adulthood, Kerns said.
"Every time the [queen] gets pregnant, her intervertebral disc space — the space between her vertebrae on her spine — will get just a tiny bit bigger, and then bigger and bigger every time she has a litter," Kerns told Live Science.
At her peak, the queen can give birth to a litter of 33 babies, each about the size of a "robust kidney bean," he said. This litter size is the largest of any mammal on Earth, Kerns said.
The prehensile-tailed porcupine (Coendou prehensilis) from South America goes through two extreme events during birth. For starters, these porcupine babies are born fully quilled. The quills are soft in the womb, but harden once exposed to air. Still, giving birth can be difficult, especially if the baby is born breech (bottom first), Kerns said.
The second extreme factor comes from the place of the birth: a tree. Kerns said he has never seen a newborn porcupine fall out of a tree, but it likely happens in the wild occasionally.
"The last one we had here [at the National Zoo], we watched him cling for dear life onto a branch while the umbilicus was coming off," Kerns said.
The tiny tenrec looks like a cross between a shrew and a hedgehog, but it is neither. In fact, this animal is more closely related to the elephant than to either of these animals.
Tenrecs are covered with spines. Unlike the porcupine, whose quills have barbs that can get stuck in the skin of predators, the tenrec keeps its spines its entire life.
Still, just like the porcupine, the tenrec mother must give birth to a spiky baby. The spines are soft in the womb but harden once they hit the air, as with the porcupine. But the prehensile-tailed porcupine usually has just one baby at a time. Tenrecs have between two and 10 babies per litter, which is a lot of spikes to deal with, Kerns said.
Short-eared elephant shrew
The short-eared elephant shrew (Macroscelides proboscideus) is tiny; it measures about 4 inches (10 centimeters) long and weighs no more than 1.5 ounces (43 grams), according to the National Zoo.
But Mom's weight can increase by 50 percent when she has two babies. Each newborn weighs about 0.3 ounces (10 g), so a litter of two would weigh about twice that.
"Think about being 40 g [originally] and having 20 g [0.7 ounces] worth of baby," Kerns said. "That is half of your body weight when you're not pregnant that you just gave birth to."
The giraffe's birth is extreme because of the long drop the baby takes the moment it enters the outside world.
In a typical giraffe birth, the baby's front hooves poke out of the mother first, followed by the nose and head. After about 30 to 60 minutes of labor, the mother pushes the baby out. Then, the calf unceremoniously drops about 6.5 feet (2 meters) to the ground, making a terrific thud.
It might sound inhumane, but the fall is necessary. It ruptures the amniotic sac, allowing the baby to start breathing on its own, Laurie Holloway, a spokesperson for the Dallas Zoo, told Live Science in 2011.
Spotted hyena births are not for the faint of heart. In the final stages of pregnancy, high-ranking female spotted hyenas (Crocuta crocuta) expose their fetuses to high levels of androgen, a male sex hormone linked to aggression, Live Science previously reported.
This extra androgen can make the pups more aggressive, giving them an edge over their peers, but it can also cause the mother's reproductive organs to grow. For instance, the clitoris, which contains the birth canal, can extend 7 inches (18 centimeters) from the body, Kay Holekamp, a professor of integrative biology at Michigan State University, told Live Science in 2006.
"Imagine giving birth through a penis," Holekamp said. "It's really weird genitalia, but it seems to work. Although giving birth through a 'penis' isn't a trivial problem."
What's more, the hyena's birth canal is just an inch (2.5 cm) in diameter, and a 2-lb. (0.9 kilograms) pup can rip through the tissue as it exits the mother. Poor Mom can die from these rips, as is evidenced by the high death rate among first-time hyena mothers, Live Science reported.
The kiwi's egg occupies up to 25 percent of its mother's body, making it the largest egg, proportional to body size, of any bird in the world, according to the American Museum of Natural History (AMNH) in New York City. That's one egg-treme egg to lay!
Due to the egg's size, kiwi birth is equivalent to a chicken laying a 1-lb. (0.4 kg) egg or a human giving birth to a 4-year-old child, according to Audubon.
Luckily, there's an upside to mom's large load. The egg is so big that the baby is fairly developed by the time it hatches, according to the AMNH.
Humans can also have extreme births. For one thing, it can be fatal to the mother: About 830 women die from preventable causes related to pregnancy and childbirth every day, according to the World Health Organization (WHO). However, access to health care is improving, the WHO said. Between 1990 and 2015, maternal mortality dropped by about 44 percent worldwide, the WHO reported.
Even when it's not deadly, human birth can be extreme for the mother. Women who go into labor experience contractions, a tightening of the uterus that works to push the baby down the birth canal, according to the American Pregnancy Association. Their cervix dilates, and then they push until they evict both the baby and the placenta.
If a cesarean (C-section) is needed, doctors will make an incision through the abdominal and uterine walls so that the physicians can pull out the baby, the association said. In the United States, about 32 percent of all births are C-sections, according to the Centers for Disease Control and Prevention.
Human babies need a lot of TLC — tender love and care. But they can help make a loving family … and maybe even a Mother's Day card if they remember when they're older.
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Laura is the archaeology and Life's Little Mysteries editor at Live Science. She also reports on general science, including paleontology. Her work has appeared in The New York Times, Scholastic, Popular Science and Spectrum, a site on autism research. She has won multiple awards from the Society of Professional Journalists and the Washington Newspaper Publishers Association for her reporting at a weekly newspaper near Seattle. Laura holds a bachelor's degree in English literature and psychology from Washington University in St. Louis and a master's degree in science writing from NYU.