Originally Posted by CaliGirl
BB is not aggressive, he is very mellow, easy-going kitten overall. That is why we were shocked at that. His Pokey, to say it nicely, was out and all. I just thought that males usely don't start that behavior till they are around six months. Thank you all for the wonderful advice, any other advice would be greatly appreciated. Jenny
If BB (cute name by the way!) is mounting a female with his "pokey" (LOL) out at the age of 3 and a half months, then I can see where you might be pursuaded to think the behavior was indeed sexual in nature. However, that now being said, unless his testicles are fully descended (at 3.5 months they normally aren't) this behavior is dominance. Males at BB's age do not have testosterone yet and they won't until the testicles are fully and completely formed and have mostly descended into the scrotum. Males usually don't begin to sexually mature until 6 or so months of age at the earliest, however I have heard of a very few cases where it began as early as 5 months. Even so, your kitten is only 14 or so weeks old (you DO know his age for a fact, right? You mentioned you also had his mother there so I presume you know the date she gave birth) and they normally just don't have the necessary equipment nor do they have the necessary hormones to exhibit sexual behavior yet at that age.
If your vet is comfortable neutering now or soon, then that may help some with BB being dominant over his mother. But even then, it may not. Cats in multiples will always establish a very firmly set hierarchy - there is always an alpha and there are always those "beneath" him or her. Unless you are dealing with sexually mature adult intact cats (that is to say, cats of an age sufficient to reach maturity but who are not sexually altered) mounting behavior is a cat's way of telling other cats that he or she (yes, even females will mount other cats) is the boss of them and that they had better do as he or she pleases or else they will get mounted (or worse!) and forced to be submissive. Little boy kittens are famous for doing this to their Moms when they get to be around your BB's age. I've seen it in my own kittens and cattery. They are like little human toddlers - "MOM! I can DO IT myself, leave me alone!!!" and they get frustrated with Mom for simply BEING Mom ... little toddlers will throw or kick or slap at their Moms but little boy kittens will try to mount Mom to force her submission.
Unless BB is actually penetrating your female, then there is really not much you can or should do to stop the behavior. Most of the time, Mom will turn around and slap the bejeeeezes out of a kitten doing this and they learn not to do it anymore unless they are willing to get beat up by Mom. Is Mom cat already spayed? If not, then get that done now and until you can, if you see BB actually "hit the mark" so to speak, separate them.
It is good that you don't observe any aggression yet. It could come to that though, just so you can be prepared to intervene if Mom cat doesn't stand up for her rights.
Hoping this helps,