I own a few zebra finchs and one of them has hurt his leg or something. I took picture if anyone know what to do with that. It seems pretty bad but I didn't notice anything before yesterday, he seemed really healty and was very active before that and today he can't even stand on the bad leg and he's not quite active

My parents don't want me to go see a avian vet for such a tiny bird so I would appreciate if anyone could give me some tips that I could try at home.