
Some of the first animals documented engaging in same-sex behavior were beetles (cockchafer beetles, funnily enough!) This was during the 1800s. And it caused quite a moral panic in the scientific community. Because if it was natural in animals, it could theoretically be natural in humans.
To add on, another really famous one was the lesbian sea gulls of Santa Barbra island. 1977 study that found that about 10% of the birds there lived in lesbian pairs and raised twice the number of eggs as the straight couples, also mated cloaca to cloaca like males do. Was very controversial and rejected by lots of people at first; ruffled some feathers 😅