Animal behaviorists tell us that same-sex affection, intimacy, bonding, and sex are common among non-human animals, particularly mammals.
For example, a piece on LiveScience.com said about American bison that
Homosexual [sic] mounting between males tends to be more common than heterosexual [sic] female-male copulation among American bison, especially because females only mate with the bulls about once a year. During mating season, males engage in same-sex activities several times a day. More than 55 percent of mounting in young males is with the same gender.
It should be noted that by "mounting" the article does not mean anal penetration -- it means frottage, that is, erotic rubbing, as when a male dog "mounts" your leg and rubs his penis against it.
About walrus, the article notes that
Male walruses don't reach sexual maturity until they are four years old. During that time, they are most likely exclusively involved in same-sex relationships. The older males are typically bi-sexual, mating with females during breeding season and copulating with other males the rest of the year. Males rub their bodies together, embrace each other and even sleep together in water.
And many other species rub bodies together, and rub phalluses together, including dolphins, whales, manatees, and bonobos.
We discuss those animals in our Man2Man Alliance article Frot Among the Animals.
See also Sex Between Men: An Activity, Not A Condition.