Female rabbits can also exhibit 'male' sexual behaviours eg. humping, mounting etc.
My female dog Pippa will actually mount our male dogs when our other female Lucy goes into heat, and will 'hump' them.
Humping is also a sign of dominance (this act of often not sexual in nature at all), and, as you mentioned in another thread, it is possible that you have quite a dominant bunny on your hands. Neutering/spaying can lesson or completely stop any of this kind of behaviour, alongside aggression, territorial issues, spraying, and improving litterbox habits.
kmtangelkrystal Are you talking about nipples? I think male rabbits also have nipples- why wouldn't they? Our male dogs have nipples, male cats have nipples, men have nipples!! They just aren't nearly as noticeable or prominant in males as they are in females- nipples are especially prominent in females that are pregnant, and those that have given birth (they often seem to "go down" fully after an animal has had pups/kits etc. )
How old are your kits? Is it possible to determine their sex yet? If so, then I would recommend that as the most reliable way to work out if they are male or female- it's still not great, but it's the best you have until bunny balls start to appear
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Jen