A Barbary macaque grooming a deer © Arterra / Getty
A large proportion of animal odd couples have involved zoo animals or domesticated ones.
This may in part be because rare behaviours are hard to spot in the wild or because the zoo environment can provide limited opportunity for social intereaction with one’s own species, says Cedric Sueur of the University of Strasburg.
“In captivity, animals can’t express their full behavioural repertoire,” he says. “In zoos, a gibbon and an orangutan caged together readily become ‘friends’ and groom each other.”
Nico de Bruyn of the University of the Pretoria led the team who observed macaques riding sika and attempting copulation, in a natural setting on Japan’s Yakushima Island.
“My sense is that these behaviours are more common nature than we think,” says de Bruyn.
It is thought that some of the unusual adoptions, friendships and copulations could be caused by a range of hormones.
For example, a lioness that has recently lost its cubs will still have high levels of hormones that drive parent behaviour – such as prolactin and oxytocin – which may drive their ‘adoption’ of antelope calves.
“They see them as their babies beacuse of their small head and big eyes,” says Sueur.
“However, the end is never happy.” If the adoptive lion doesn’t turn on her charge once her hormonal surge subsides, it’s likely that another member of her species will.
In other interactions, there may be mutual benefits for both parties, such as working together to catch prey or to look out for predators.
From prey to ‘friend’
Keepers at Russian safari park had introduced Timur the goat into Amur the tiger’s enclosure as live prey. But there was no swift, clinical dispactch as you would expect when a big cat is presented with the opportunity to feast on the freshest mutton.
Instead, the pair seemed to become inseparable. Timur would trot around happily behind Amur as he did his rounds, and Amur would even allow Timur to share his shelter.
Dream marine team
Roving coral groupers and moray eels hunt together cooperatively to their mutual advantage.
The groupers hunt in open water, the morays in holes and crevices, leaving prey with nowhere to hide. The groupers use sophisticated signals to indicate the prey’s position to their collaborators.
To the rescue
Accounts of humpback whales disrupting orca attacks on seals and other species have been widely reported as evidence of incipient morality among cetaceans, but it is probably more akin to songbirds mobbing raptors that endanger their own offspring.
In the Bahamas, male bottlenose dolphins regularly copulate with female Atlantic spotted dolphins and sometimes produce hybrid offspring.
More frequently, though, these cross-species copulations occur between males. The behaviour is thought to be more about aggression than reproduction.
In 2012, two male Humboldt penguins, Jumbs and Kermit, paired up at Wingham Wildlife Park in Kent, despite the availability of single females.
The couple have been used by the zoo to raise chicks abandoned by more conventional couples.
A guest staying in a lodge in Tanzania captured the first ever evidence of cross-species suckling in wild cats.
They spotted and photographed a lioness, a five year old known locally as ‘Nosikitok’, nursing a three week old leopard cat.
Click here to view the photos of this big cat ‘adoption’
A full length version of this article is available in the April 2017 issue of BBC Wildlife Magazine