Gender Issues

Question
QUESTION: I noticed an interesting activity between my two young (supposedly female) pet rats tonight.  One is smaller while the other is just slightly larger (both small in size).  While running around their cage and playing, I heard some noises that sounded like rough-housing.  While taking a closer look, the slightly larger one was trying to mount the smaller one from behind.  I broke the play up with a spray of water next to them, because I wasn't really sure what was going on.  This activity happened repeatedly over the next hour or two.    I looked to re-investigate, and both of them appear to have the same genitalia, no visible testicles.  Both have what look to be sets of nipples raising from their back legs to their mid-underbelly.  



I guess my question is, since they have nearly identical undersides, is it safe to assume they are both female?  And if so, have you ever seen behavior like this, and if yes, how should i interpret it?

ANSWER: Hi Marc

This is totally normal for both sexes to do this. Its is simply an issue with domination, it may be sexual in nature, but probably is safe to say its not and simply just the larger rat showing the smaller rat who the boss is.

However, how long have you had these girls?  Males have an open inguinal canal which in turn can be a perfect hiding spot for his testicles since he can draw them up inside due to the inguinal canal being open and thus can throw off the novice rat owner (and even some not so new rat owners too!!)
The fact that you see nipples in both rats is pretty much proof that you have two females, however, but males do have mammary tissue, minus the nipple.

To be super sure though, you can check out my website to compare male and female rats (young rats, that is since its totally obvious once the male is more mature that he is a male since he has a fairly decent pair of rug burners, and that is about as unprofessional as I can get about that!  LOL!


Here is the URL:

http://www.freewebs.com/crittercity/healthcare.htm


Hope this helps!

---------- FOLLOW-UP ----------

QUESTION: They've been with us for around a month now, and seemed pretty young when we got them from the pet store.

Answer
Rats are sexually mature and can reproduce as young as 5 weeks old so if you had a pair of opposite sex rats, chances are the female may be pregnant, but again, if you see nipples on both rats, they are most certainly female with the bigger one taking on the alpha female role of the cage. Its common and normal rat behavior.  Us women....we need to be in charge, even if over a member of the same sex!

LOL!!