Friends and enemies in the animal world tend to be pretty clear-cut — there are some species that just weren’t born to get along. But as these unlikely pairs show, even Mother Nature doesn’t set things in stone: Who says that orangutans and tigers, dogs and deer, cats and birds can’t all be friends somehow?

From a sheep that brought a baby elephant out of a deep depression to natural enemies that snuggle down together for every nap, these 10 heart-wrenching relationships are incredible and unforgettable.

The Pigeon and the Macaque

Take this macaque, for example, who, according to The Daily Mail, was rescued from Neilingding Island in China after his mother abandoned him and left him for dead: His recovery was dragging until he made friends with this pigeon, and now the two are rarely apart. Photo via The Daily Mail

The Sheep and the Elephant

The Daily Mail reports that the first time Albert the sheep met Themba the elephant at the Shamwari Wildlife Rehabilitation Centre in South Africa, he didn’t exactly roll out the welcome mat: The baby elephant, orphaned at six months old when his mother fell down a cliff, chased his new friend Albert until the sheep took refuge in a shelter — for 12 hours. But since then, the animals have been “inseparable,” say observers, napping together, walking together, and even picking up habits: Albert figured out how to eat thorny bushes by following Themba’s lead to avoid the spikes. Photo via The Daily Mail

The Cat and the Chicken

Cats and birds are not known for their peaceful relations (just ask Tweety and Sylvester), but Snowy and Gladys are the exceptions to the rule. Gladys was a two-day-old chick when she became the only hen to survive a fox attack on her farm in Suffolk, England, but when her owners brought her inside for added safety, she found an unlikely ally in Snowy the cat. The owners saw the cat washing the chick and keeping her clean, and when it was time to let her back outside, Gladys refused to go without Snowy. The two still play together and, according to The Telegraph, are “the best of friends.” Photo via The Telegraph

The Tiger and the Pig

Pigs and tigers seem like they’d be natural enemies, but in captivity, that’s not always the case: These photos from the Sriracha Tiger Zoo in Thailand show a tiger nursing a litter of piglets (and this tiger herself was raised by a pig). But while the process isn’t unheard of, this set of images brings up bigger issues: Officials believe that the photos were staged (and the animals were harmed to get the shots) for publicity. Photo via Animal Liberation Front

The Deer and the Dog

Mi-Lu and his sibling are believed to be the first two Pere David deer born in captivity — which was a good thing for the rare species, but a bad thing for Mi-Lu, whose mother rejected him, the BBC says, to raise her other fawn (it sounds harsh, but scientists think the rarity of deer twins meant that the mother didn’t know how to take care of a second baby). The two resident dogs at Knowsley Safari Park where Mi-Lu was born — Geoffrey and Kipper — stepped in to help raise him, going for walks and snuggling as a group, until the deer was introduced back into the herd. Photo via Hamburger Abendblatt

The Hippo and the Tortoise

Even a 130 year age difference can’t come between these BFFs: Owen the baby hippopotamus and Mzee the giant tortoise have been friends since Owen was rescued from a reef where he was stranded during the 2004 tsunami in the Indian Ocean and brought to Lafarge Ecosystems’ sanctuary in Kenya. The frightened hippo ran right over to the surprised tortoise and hid behind him — just as he would have hidden behind his mother — and, since then, the two have been walking and feeding together each day. They even have their own line of books and a Web site. Photo via The Age

The Cat and the Chihuahua

credit: Migrated Image

When this baby chihuahua lost his mother right after she gave birth, the staff at Arizona’s Halo Animal Rescue had the impossible job of trying to find another nursing dog to take over — and with no dogs available, they turned to the next best thing: a cat. The feline was already nursing four kittens that were about the same size as the puppy, so rescue workers introduced the chihuahua into the litter. A week later, the dog was doing well, gaining weight, and nearly ready to be adopted. Photo via AZ Family

The Cat and the Red Panda

This mama cat had an even more unusual nursing applicant: a baby red panda. After its mother left, the panda joined a group of kittens being raised by a house cat at the Artis Zoo in Amsterdam, says MSNBC. While the endangered animal would have lived for about three months on a liquid diet before switching to bamboo and fruit, the panda tragically died after choking on milk a few weeks after the cat adopted it. Photo via PetSugar

The Tiger and the Orangutan

You’re not likely to find a wild Sumatran tiger that’s friends with a wild orangutan, but at the Taman Safari animal hospital in Indonesia, abandoned primates Nia and Irma have no problem snuggling with Dema and Manis — month-old tigers. Both species are endangered, but in the sanctuary they enjoy the same activities as their wild brothers and sisters: cat naps for the tigers and rope swinging for the orangutans. Photo via The Daily Mail

The Lion and the Humans

Christian the lion wasn’t found in the wild: He was bought at Harrod’s in the 1960s by John Rendell and Ace Bourke, who raised him in their flat until he outgrew the tiny living space and was released into the wild. But nine months after Christian took over a pride of his own, his former owners traveled to Africa for one last goodbye — and found a lion that was as gentle and kind to them as he’d been as a cub.