The animal kingdom can be ruthless to young animals — and sometimes, dad's not around to help. These meticulous mothers go to extremes to ensure the survival of their offspring, and they deserve some credit for their efforts.

Giant Pacific octopus

Giant pacific octopus in den

The giant Pacific octopus doesn't even leave her thousands of eggs in order to get food. (Photo: Ratha Grimes/flickr)

The giant Pacific octopus is perhaps the hardest-working marine mom, laying up to 100,000 eggs and painstakingly caring for them for months without leaving them — not even for food. By the time the little guys hatch, she spends her last bit of energy helping them out of the den ... and then she dies. Check out this amazing video that documents the octopus mother caring for the eggs as they hatch over the course of a week:

Jump to minute 3:24 for the most breathtaking footage.

***

African elephant

African elephant and calf

Elephants are pregnant for almost two years. (Photo: Johan W. Elzenga/Shutterstock)

Elephants have the longest gestation period of any mammal — nearly two years! Pair that with the fact that no other land animal gives birth to a larger baby, and you've got one seriously durable mother. Elephant calves can nurse for three to six years after birth, but luckily, elephant moms don't have to rear their kids alone: They have the help of the herd, which is comprised entirely of females and their calves.

***

Grey kangaroo

Eastern gray kangaroo with joey in pouch

Grey kangaroos can have two joeys in their pouches at once. (Photo: Jiri Haureljuk/Shutterstock)

Grey kangaroos are nearly permanently pregnant and can have two joeys in their pouches at the same time — until the younger sibling gets larger and two becomes a crowd. Joeys will not venture out until they are 9 months old, and after that they only hop out for an adventure once in a while. Joeys become completely independent about a year after their first hop out of the pouch. See a grey kangaroo give birth to a baby and follow its development in the incredible footage below from BBC's "Life of Mammals":

Skip to minute 1:03 to avoid the (not so adorable) childbirth.

***

Virginia opossum

Virginia opossum carrying joeys

Virginia opposums can have more than two dozen babies in one litter. (Photo: Donna Heatfield/Shutterstock)

Incredibly, the Virginia opossum can have anywhere from four to 25 babies in a single litter! But because marsupials can only feed one joey per nipple, the most opossum joeys that can attach is 13 — still, imagine fitting that many mini-marsupials into one pouch! Of course, they don't hang out in there for too long, usually leaving after 70-125 days.

***

Emperor penguin

Emperor penguin and chick

Emperor penguin mothers have to walk miles and miles in the snow to get food for their chicks. (Photo: BMJ/Shutterstock)

Not only do female emperor penguins have to lay a huge egg, but then they have to leave it behind to walk as far as 50 miles in the snow in order to gorge themselves on fish — and they can't even keep all the fish down! They make the trek back to regurgitate their feast to their chicks. (But we can't discount what the male emperor penguin goes through while she's gone: He stands in a huddle in frigid winds, protecting the egg between his legs until it hatches.)

***

Strawberry poison dart frog

Strawberry poison dart frog on bromeliad leaves

The strawberry poison dart frog mom carries her tadpoles to the tallest trees in the forest. (Photo: Luis Louro/Shutterstock)

While the emperor penguin mother goes the distance for her chick, the strawberry poison dart frog climbs great heights for hers. She lays her eggs on the Costa Rican rain forest floor, and once they become tadpoles, carries them one by one to different tiny pools of water — usually in bromeliad leaves, but sometimes to the tallest trees of the rain forest canopy. She then proceeds to feed each of her tadpoles with unfertilized eggs until they become fully developed. That's dedication!

***

Orca

Orca and calf

Orca mothers don't sleep for a month because their babies don't. (Photo: Monika Wieland/Shutterstock)

If you think new human mothers get too little rest during the first month of their newborn's life, the killer whale's story ought to put things into perspective. Orca calves hit the water running, so to speak, and don't sleep a wink for the first month of their lives — which means mommy orca doesn't sleep either! Instead, they continuously swim, which helps them to avoid predators and build important muscle and fat reserves. (And before you go thinking that whales don't sleep like we do: they actually have a similar schedule to humans, floating motionlessly for between five and eight hours every night!)

***

Taita African caecilian

Caecilian

The Taita African caecilian grows skin for her babies to eat. (Photo: Geoff Gallice/flickr)

This wormlike amphibian mom gives the skin off her back — literally. Once her eggs have hatched, she grows an extra, nutritious layer of skin that she allows the children to eat. She regrows it every three days until her squirmy young become more independent.

***

Tailless tenrec

Tailless tenrec in burrow

The tailless tenrec can have more than 30 babies at once. (Photo: Frank Vassen/flickr)

OK, back to the cute animals! The tailless tenrec of Madagascar can give birth to up to a whopping 32 babies, with an average litter of 15-20. That's a lot of mouths to feed! Though they usually have 12 nipples, some females have been found to have up to 32.

***

Frilled shark

Frilled shark

The frilled shark may be pregnant for more than three years. (Photo: © Citron/CC-BY-SA-3.0)

Though little is known for certain about the mysterious, deep-dwelling frilled shark, scientists think these females have the longest gestation period of any vertebrate — up to 3.5 years! One explanation for this extra-long pregnancy is the slow metabolism of this cold-water critter. Its young develop in eggs inside the female and she gives birth to her tiny shark babies once they are fully developed.

***

Hammerkop

Hammerkop flying with nest materials

The hammerkop spends months building a huge nest for her young. (Photo: Dave Montreuil/Shutterstock)

Hammerkop nest in acacia treeOver the course of three or four months, these African birds will work a few hours each day creating a gigantic nest for their young.

The male collects materials while the female puts the intricate nest together, and then they both cover it in mud and decorate it. The final product can be as large as 5 feet wide and 5 feet tall, often weighing in at over a thousand pounds.

As you can imagine, it's very durable and quite a valuable piece of real estate for other birds once the hammerkops move out.

***

Alligator

Alligator carrying baby across water

Alligator mothers aren't nearly as tough as they seem. (Photo: Orhan Cam/Shutterstock)

They may seem tough on the outside, but alligator mothers are actually very caring. They know all about the ruthless nature of their wetland environment and do everything they can to protect their little ones — even if that means sticking eggs a pile of rotting compost, the heat from which incubates the eggs while the mother stands on guard. Once the eggs hatch, she'll nearly gobble them up into her strong jaws to carry them safely into the water, and then the babies stay with their mom for up to a year. Check out this National Geographic video that shows just how protective mama alligator can be:

***

Polar bear

Polar bear mother and cub

Polar bear mothers double their body weight to prepare for pregnancy. (Photo: Tom linster/Shutterstock)

It's not easy being one of the few Arctic species, and it's even harder to be a single Arctic mom. To prepare for pregnancy, the female polar bear must double her body weight (gaining upwards of 400 pounds!) and after that, she doesn't eat for several months, staying underground with her cubs for a full two months after they're born. Then she must navigate the ever-melting sea ice in search for food to keep herself and her cubs alive for the next two years, until her cubs become independent. Sir David Attenborough says it best in this clip from BBC's "Planet Earth":

***

Orangutan

Mother and baby orangutan climbing

Orangutans nurse for about five years. (Photo: Sergey Uryadnikov/Shutterstock)

Young orangutans remain dependent on their mothers for the longest of all primates besides humans, nursing for about five years and generally sticking around for up to nine years. On top of looking after the tiny, tree-climbing cuties, orangutan mothers must build a new treetop bed for them to sleep in every single night — more than 30,000 homes in a lifetime! Like our own mothers, orangutans teach their children everything from home ec (building study nests) to etiquette (finding food and eating it gracefully).

***

Hornbill

Female knobbed hornbill

Hornbills seal themselves into a tree with their chicks. (Photo: Sergey Uryadnikov/Shutterstock)

Hornbills have a very peculiar — but undoubtedly safe — nesting habit. The mother bird seals herself inside the hollow part of a tree with mud, fruit and other things. She leaves an opening that's just wide enough for dad to sneak snacks through for her and the chick. Some hornbill moms will break out of the wall and rebuild it to keep the chick safe for a while longer. This video from BBC's "Jungle" gives a rare and intimate glimpse into the hornbill's nest:


***

Photo credit (hammerkop nest): Batra/CC-BY-SA 3.0