In 2020, a viral video of an unusual interaction between a badger and a coyote captivated the internet. Filmed by a remote-sensing camera in the Santa Cruz Mountains of California, the footage shows the two animals entering a canal to pass under a highway. Wagging his tail, the coyote bounded toward the badger and then moved away from him, pausing to see if the badger would follow. The badger hurried to catch up with his companion and they entered the tunnel together.
Their playful demeanor suggested the pair shared a friendly bond. But can animals really be friends, like humans?
In many species of social animals, certain behaviors suggest that individuals may indeed be closer to some than to others (other than kin or mates). Male sponge-feeding dolphins associate with other males that have a similar style of food. Elephants use specific greetings to other elephants they know. Primates demonstrate intimate bonds with non-kin through grooming. Rooks are also known to groom several rooks in their flock, preceding them with their beaks.
“Individuals create social relationships to navigate their environment,” said Delphine De Moor, a postdoctoral researcher in behavioral ecology at the University of Exeter in the United Kingdom. For highly social animals, relationships are defined by varying levels of trust and intimacy, De Moor told Live Science. Patterns of interaction shape these connections; trust grows when repeated interactions are positive.
If animals can form bonds that are stable, enduring and mutually beneficial — qualities found in human friendships — “then we see friendship in the animal kingdom,” De Moor said.
Scientists studying primates have found that neurochemistry plays a major role in strengthening such connections, according to Catherine Crockforddirector of research at the French National Center for Scientific Research (CNRS) in Lyon and head of the Great Ape Social Mind Laboratory.
In primates, grooming releases the behavior-regulating hormone oxytocin, “which then feeds into the reward center, apparently providing a positive feedback system so that you’re more likely to groom again,” Crockford told Live Science. . Caring for a friend also reduces cortisol, a stress-related hormone. In contrast, cortisol levels were not affected when the monkeys cared for an unrelated group member, Crockford added.
“There seem to be these physiological benefits that you get from doing something like grooming specifically with a relationship partner,” she said.
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Scientists first reported primate reciprocal friendship through observations of matrilineal monkey groups, but recent decades have presented a growing body of evidence about friendship and its benefits in other mammals, Crockford said.
“Individuals who manage to maintain these strong relationships end up living longer, have more offspring, and exhibit fewer stress-related traits,” she said. “It really seems like if you’re able to maintain these kinds of relationships, they have very profound benefits.”
For example, killer whales share food and information on where to find food; orcas that have strong bonds in their group are less likely to starve when resources are scarce. Hyenas with more friends tend to achieve greater success within their clans, as they reserve social challenges.
But with friendship comes responsibility, added De Moor. “At some point,” she said, “animals are willing to take more risks, much more costly behaviors for their preferred social partners.”
Consider the self-sacrifice of a vampire bat helping a starving friend sharing of recently ingested meals and throwing up blood in a friend’s mouth (and if you haven’t vomited in your friend’s mouth lately, can you call yourself a friend?).
Among chimpanzees, bonds of friendship can be so strong that if a mother dies and leaves a dependent child, “then a male or female friend. [of the parent] can adopt that offspring,” Crockford said. Raising a minor comes at a cost to the new parent, especially if the adopter is male, she added.
“His overall pace of life needs to slow down,” Crockford said. “He’s going to have to carry the offspring or go at their speed and share his nest with them at night, and he can’t engage as easily in group interactions or aggressive interactions with others.”
Friendship between species
Mutual trust can also occur between species. In 2022, a groundbreaking study showed that wild chimpanzees and gorillas in the Republic of Congo can reach across the species barrier to form friendships that last 20 years or more.
In some cases, animal friendships are created by human intervention. Cats and dogs who share a home often develop close bonds. In a private zoo in Belgium, a family of the orangutans befriended a mob of ottersafter zookeepers combined their habitats. A lion and a dog in Mexico who were raised together (the lion was kept illegally as a pet) remained close after the two were moved to an animal rescue facility.
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While the display of playful friendship between a badger and a coyote in California had never been observed before, such interspecies relationships may be more common in nature than scientists suspect, De Moor said. Much more is known about animal friendships in some groups—primates, elephants, and dolphins, for example—simply because their social behavior has been observed for many decades, with some relationships studied over the animals’ lifetimes.
“We only know what we study and we don’t know what we don’t study,” said De Moor.
Evidence of friendship among animals in general (and primates in particular) sheds light on the evolution that shaped the human capacity for friendship, Crockford noted. Our last common ancestor with apes lived about 25 million years agoso the neurochemistry behind human friendship and related behaviors has been around for millions of years.
“These mechanisms are deep and ancient,” she said. “In this day and age, where there are other things that people can prioritize over friendship — like money, fame, or clicks — it’s a very nice reminder that a fundamental part of us is designed to have friends. And if we manage to have friends and we’re serious about our friends, we’ll live longer and be healthier and less stressed.”