I have often heard the claim that homosexuality exists in non-human animals. Sheep and dolphins seem to be common examples. I find it easy to believe that homosexual activity exists - some animals just get so horny that they will try and have sex with anything. But this is not really what we think of as homosexuality in human terms.
So, are there any documented examples or studies of exclusive homosexuality in non-human animals (preferably mammals) where
- There are clear, well defined male and female genders,
- The majority of sexual activity in the species occurs between opposite gendered individuals,
- There are examples of specific individuals that always prefer same-gendered sexual activity rather than opposite-gendered sexual activity, even when both are available.