List of mammals displaying homosexual behavior

These animals have been observed practicing homosexual courtship, sexual behavior, affection, pair bonding, or parenting.

Bruce Bagemihl writes that the presence of same-sex sexual behavior was not officially observed on a large scale until the 1990s due to possible observer bias caused by social attitudes towards LGBT people, which made homosexuality in animals a taboo subject.

[3][4] He devotes three chapters, "Two Hundred Years at Looking at Homosexual Wildlife", "Explaining (Away) Animal Homosexuality", and "Not For Breeding Only" in his 1999 book Biological Exuberance to the "documentation of systematic prejudices" where he notes "the present ignorance of biology lies precisely in its single-minded attempt to find reproductive (or other) "explanations" for homosexuality, transgender, and non-procreative and alternative heterosexualities.

Bagemihl's research shows that homosexual behavior, not necessarily sexual activity, has been documented in about 500 species as of 1999, ranging from primates to gut worms.

This is a list of some mammals that have been recorded engaging in homosexual behavior, which is part of a larger list of animals displaying homosexual behavior including birds, insects, fish, etc.