From Wikipedia, the free encyclopedia
Two goats and a cat keeping each other company while staying cool in the shade

An interspecies friendship is a nonsexual bond that is formed between animals of different species.[1] Numerous cases of interspecies friendships among wild and domesticated animals have been reported and documented with photography and video.[1] Domestication of animals has led to interspecies friendships between species that would never naturally exist together. In many cases of interspecies friendship, the species are not normally seen together, and sometimes, one is of a species that ordinarily preys on the other in nature.[2]

The concept of interspecies friendship is similar to that of mutualism in that two individuals from different species exist in a relationship where each organism benefits from the activity of the other. Reasons for the formation of interspecies friendships include domestication, interspecies communication, mutually beneficial exchanges, desire for social bonding, protection, or is often unknown.[2][3][4]
Friendships between humans and other animals
Main article: Pet
Dogs
A human with her dog companion
Main article: Human–canine bond

The relationship between a human and a household dog (Canis lupus familiaris) is quite common and said to be similar to the relationship seen between a parent and child.[5] Many people agree that there is an emotional bond between themselves and their dog.[6] An important indicator of the bond between a dog and its caregiver can be seen through separation and reunion incidences. The behaviour of the dog including approach latency and the frequency of initiating physical contact varies according to how familiar the dog is with the person.[7] This can be viewed as a snapshot of their relationship.[6] Behaviours such as tail wagging, lip licking, body shaking and vocalization also indicate this.[6]

The relationship between humans and dogs is so impactful that therapy dogs are a common practice. From hospitals to schools, dogs help comfort humans.[8]
Cats
A human petting a cat
Main article: Human interaction with cats

Friendships between household cats (Felis catus) and humans are also very common. The relationship between cats and humans dates back over 10,000 years. Cats even had great influence in ancient Egypt.[9] Today, cats live in many countries and are the most popular choice of pet.[10][11] Cat owners often consider their cat as an integrated part of their family and indicate that they are easy to care for and engage in social behaviours such as allowing humans to hold, pet and play with them.[10][11] Mutual affection and bonding is displayed between cats and their owners, indicating a sense of friendship.[11]
Horses
A human touching a horse's muzzle

Friendships between humans and domesticated horses (E. ferus) are often observed and occur when the horse is willing to allow the person into its flight distance and personal space through friendly interactions such as grooming, scratching and rubbing.[12] Horses are social animals and once a person is accepted into their personal space, they become a part of their social system.[12] A domesticated horse will work hard for praise from its human partner and can be easily trained to respond to human commands.[12] Many people report strong feelings of friendship with their horse and believe that their horse considers them to be its friend, protector, and caretaker.[13]
Non-domesticated animals

Interspecies friendships have been displayed between humans and non-domesticated animals. Some examples include:

The interspecies friendship between zoologist Dian Fossey and a group of gorillas.[14] Fossey developed relationships with the gorillas she studied and after years of being away from them, they recognized and remembered her when she returned. After their reunion, the gorillas engaged in amicable behaviour with Fossey such as direct eye contact, sniffing, crooning, resting beside each other and embracing one another.[14]
The relationship between Barbara Smuts and a baboon troop.[15] Over the course of many interactions between Smuts and the baboons, eventually the baboons treated her as if she was a part of their troop. Smuts would comfortably rest with them, exchange friendly glances and felt safe amongst them.[15]
Friendly encounters have been observed between gray whales and humans.[16] Gray whales seem to enjoy when humans pat them alongside boats. During these human-whale interactions, the whales are generally timid and gentle.[16]

Friendships between non-human animals
A cat and dog bonding
Dogs and cats
Main article: Cat–dog relationship

Dogs (Canis lupus familaris) and cats (Felis catus) that coexist in close quarters are two unrelated species that often display companionship towards each other.[1][17] Many coexisting dogs and cats exhibit friendly relationships involving behaviours such as playing and sleeping together, grooming each other and understanding differences in body language and communication.[17] Dogs and cats often engage in mutual nose sniffing which is a form of greeting displayed in cats that is not normally observed in dogs. Dogs may acquire this behaviour from the understanding of cat communication signals.[17]
Other examples
A Tufted gray langur (Semnopithecus priam) stroking a Grizzled giant squirrel (Ratufa macroura) caringly at Yala National Park, Sri Lanka

There are many documented instances of unusual interspecies friendships. Some examples include:

Three large Waders including a long-billed curlew, whimbrel and marbled godwit kept each other company every winter in Vancouver for many years.[18]
Near Cincinnati, three northern cardinal and four robin nestlings shared a nest and the parents of the nestlings worked together to bring food to their offspring.[19]
A horse and wild turkey displayed friendly behaviour in which the horse would bow down his head and allow the turkey to climb on his back.[20]
A ram and a blind cow exhibited interspecies friendship in which the ram would protect the cow by making sure she did not bump into anything and feeding beside her every day.[21] When the cow gave birth to a calf, the ram exhibited these protective behaviours on the calf as well.[21]
A cow and a blind mule formed an interspecies friendship in the Black Forest Animal Sanctuary.[4] When the species were introduced, the steer automatically assumed a protective role over the blind mule by staying near her, sleeping next to her, playing with her and leading her around the pasture to protect her from injuries.[4]
Coyotes are often known to hunt badgers, however, mutualistic relationships can develop between these rival species.[2] Coyotes and badgers engage in ground squirrel hunting together in which the badgers dig into ground squirrel nests and hunt any they come across. Ground squirrels that manage to flee the site are captured by coyotes nearby. This hunting behaviour benefits both the coyotes and badgers because it allows each species to obtain food. The coyotes initiate ground squirrel hunting through friendly behaviours such as play-bowing, tail-wagging and scampering.[2] The badgers respond to this behaviour even though they are not known to initiate these behaviours with other badgers. After the hunt, the animals often rest together with their bodies in close proximity or touching.[2]
A timber wolf and two goats were kept in enclosures next to each other in the San Diego Zoo and engaged in a playful relationship which involved racing each other back and forth by the fence separating them.[20] They would also rest next to each other by the fence and the wolf would try to lick the goats' faces. They would be let outside the same time each day so that they could play together and the wolf would only go inside at night if the goats were already inside.[20]
A miniature horse and farm goose were res