It's actually possible for all animals to be gay, even dogs. (one of my friend's friends' parents breed dogs (professionally) and they had a problem with this one male- wouldn't breed to any females. they accidentally stuck another male in with him and... came back to see them... er... getting it on... (not just mounting, but like... ugh) so yeah, it's possible)
I've heard of gay hamsters, and... my rat Haru is gay. Kei is bi, but Haru is definately gay. You'd think it was a dominance thing, but Keiren is obviously dominant over Haru now (watch them together for about ten minutes and you'll be able to tell from the body language, especially when they're around me- Kei will rarely let Haru sit by my hand so I can pet him, Kei's gotta have all the pets) but Haru will always grab onto Kei and... ugh. Yeah.
Ahaha my dad thinks my cat Pepper is gay. He's a pedigree so my dads like 'Oh, poshboy!' and he acts all smug and camp a lot, and loves being pampered...so my dad is convinced he's gay. It's really funny.
I'm starting to thing my girl Roxie is gay. I was on the computer earlier today and she kinda raped my face with her tongue. She seems to enjoy trapping me when I'm in bed and licking me to death. Either that or she's too much of a "velcro dog".