List of birds displaying homosexual behavior

For these birds, there is documented evidence of homosexual or transgender behavior of one or more of the following kinds: sex, courtship, affection, pair bonding, or parenting, as noted in researcher and author Bruce Bagemihl's 1999 book "Biological Exuberance: Animal Homosexuality and Natural Diversity".
According to Bagemihl, animal sexual behavior takes many different forms, even within the same species and the motivations for and implications of their behaviors have yet to be fully understood. Bagemihl's research shows that homosexual behavior, not necessarily sex, has been documented in about 500 species as of 1999, ranging from primates to gut worms. Homosexuality in animals is seen as controversial by social conservatives because it asserts the naturalness of homosexuality in humans, while others counter that it has no implications and is nonsensical to equate animal behavior to morality. Animal preference and motivation is always inferred from behavior. Thus homosexual behavior has been given a number of terms over the years. The correct usage of the term "homosexual" is that an animal "exhibits homosexual behavior", however this article conforms to the usage by modern research applying the term "homosexuality" to all sexual behavior (copulation, genital stimulation, mating games and sexual display behavior) between animals of the same sex.
This list is part of a larger list of animals displaying homosexual behavior including mammals, insects, fish etc.