We know that sometimes animals have unlikely friendships. Whether it's circumstances that throw them together or they just happen to find a friend from another species, animals will occasionally become pals, creating an unconventional alliance.

These unusual relationships cause a certain amount of double-takes — and they're often incredibly adorable — but there's also a scientific benefit to studying odd animal friendships.

“There’s no question that studying these relationships can give you some insight into the factors that go into normal relationships,” Gordon Burghardt, a professor in the departments of psychology and ecology and evolutionary biology at the University of Tennessee, told the New York Times.

elephant and giraffe hanging out at the zoo An African elephant and a giraffe have become unlikely pals due to the confines of a zoo. (Photo: Glass and Nature/Shutterstock)

Cross-species bonds typically occur in young animals, and they're also common among captive animals that have no choice but to seek each other out.

“I think the choices animals make in cross-species relationships are the same as they’d make in same-species relationships," Marc Bekoff, professor emeritus of ecology and evolutionary biology at the University of Colorado, told Slate. "Some dogs don’t like every other dog. Animals are very selective about the other individuals who they let into their lives.”

And when predator and prey become buddies, that requires serious trust from the animal on the prey end, Bekoff points out.

The polar bears at SeaWorld San Diego in happier times. The polar bears at SeaWorld San Diego in happier times. (Photo: samantha celera/flickr)

Animal friendships — whether in their own species or outside — can be very meaningful. Consider the story of Szenja, a 21-year-old polar bear who died at SeaWorld San Diego in mid-April after an unexplained illness including loss of appetite and energy, according to The San Diego Union-Tribune. Szenja had recently been separated from her long-time companion, Snowflake, who had been sent to the Pittsburgh Zoo & PPG Aquarium for a breeding visit. The pair had been together for 20 years. The polar bears made headlines in March when more than 55,000 people signed a petition not to separate the "best friends."

In a statement, PETA Executive Vice President Tracy Remain said Szenja died of a broken heart.

Humpty the hippo and her friend Sala the kuduHumpty the hippo and her friend Sala the kudu are orphans who became friends at a wildlife sanctuary in Kenya. (Photo: The David Sheldrick Wildlife Trust)

Here's a look at some animal odd couples that have forged lasting bonds.

http://i.imgur.com/mfCIzBD.gifv


A llama nuzzles its sheep friend. A llama nuzzles its sheep friend. (Photo: Katriona McCarthy/flickr)

squirrel hanging out with a wren This squirrel and wren are backyard BFFs. (Photo: Bonnie Taylor Barry/Shutterstock)

A pigeon hangs out with its rabbit friends. A pigeon hangs out with its rabbit friends. (Photo: Marina2811/Shutterstock)

bearded dragon and kitten are friends This kitten and bearded dragon can't get enough of each other. (Photo: ohheyitsnikki/imgur)

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.