The best overview on gay animals is from the NY Times Magazine, Can Animals Be Gay?, but the definitive work is Bruce Bagemihl’s Biological Exuberance: Animal Homosexuality and Natural Diversity. With over 700 pages of detailed information, including sketches and photographs, he provides tons of detailed information. It is hard to express what a comprehensive and entertaining work this is, while staying scientifically rigorous. Plus the portrait on the cover is amazing.

Just for fun, here is the brilliant Ricky Gervais mocking Biological Exuberance. Funny stuff, but his comment at the end about the book’s sketches is unfair, as there are plenty of photos too.