Aside from humans, the only species recorded to have lifelong same-sex partnerships is male domestic sheep (BBC). Although many species display bisexual behavior, the following five species engage in same-sex female relationships.
1. Japanese Macaques
Because female macaques exhibit more sexual positions than males, it's believed lesbian macaques simply seek more sexual stimulation. (BBC)
2. Laysan Albatross
The Laysan Albatross population on Oahu, Hawaii contain 31% female couples as pairing parents. Female albatross mate with other females for the survival of their offspring; an endeavor that takes two parents to raise one chick per season. "They rear chicks, fathered by males that are already in a committed pair but which sneak matings with one or both of the females" (BBC) And because Albatross have a tendency towards monogamy, once lesbian albatross mate, it's for life.
Bonobos, like macaques, seem to enjoy same-sex female stimulation. In a 1995 Scietific American paper by Frans de Waal, he describes female bonobos rubbing their genitals together, "emitting grins and squeals that probably reflect orgasmic experiences" (BBC). Can't say I blame them.
4. Bottlenose Dolphins
Sex is something animals use to their advantage, and it seems bottlenose dolphins aren't any different from humans. Both females and males display bisexual behaviour to help them create strong social bonds within their pods.
5. Spotted Hyenas
As matriarchs, female spotted hyenas dominate the male hyenas in the family structure, being larger in stature and physically more aggressive (Kay E. Holekamp Lab) which also seems to result in female spotted hyenas mounting other females as dominant sexual acts.