Male kitten displaying sexuality

Question
I adopted two kittens from my local ASPCA - one male and one female.  They recently visited our Vet last week (2/1) and are scheduled for spaying / neutering on 4/15 (today is 2/8).  (These siblings are about 16 weeks old.)
The male kitten is mounting and humping the female.  I don't want any more kittens!  Is this possible?  What should I do to?

Answer
Hi Mark.  Some males mature very young.  While it's most common to see a male mature around the age of 6 or 7 months, there are those who reach sexual maturity at 4 or 5 months.  Females tend to reach sexual maturity later, averaging around 9 months.  However, it isn't uncommon for a female to mature around 6 months old.  There are those who mature even younger.  Some cats as young as 5 months old have become pregnant, although this is very rare.  I think you are safe for at least another month, but you may want to see about moving the appointment to have them neutered up about a month, at least for the male.  The operation for males is very quick and simple, and all my males are neutered by 4 months of age.  The surgery for females is much more involved, and although many of my females are spayed by the age of 4 months, I like to wait until 5-6 months when the situation permits it.

There is a possibility that this behavior isn't sexually related at all, but that the male is trying to assert dominance over the female.  We often see males mounting both males and females, and occasionally females mounting other cats, when the cats are trying to determine who will be dominant in the household.  In a new environment, the rules as to who had been boss previously no longer apply, and it could be that the male is actively making a play for this position.

Nevertheless, always better safe than sorry, so I would try to get at least the male in for a neuter by the time the kittens reach 5 months.

Congratulations, and good luck!

Jessica