If this mouse is male, why hasnt he mated?

Question

Male Mouse1  

Male Mouse2   Hello,
We periodically catch mice in the house; usually keep them for a month or so and release in wild after. We caught a number of mice this fall and decided to keep them until the spring. All caught mice appeared to be females. There way be a mix of house/field mice and deer mice. When I was cleaning the cage today, I noticed that the genitals of one mouse look different than the others. Picture is attached. Is he a male? If so, how could he live in the same cage for the past 3-4 months with 2 females and not get someone pregnant?

Answer
Dear Anthony,

You have a little boy (at first I was trying to figure out what difference you were seeing between these two mice : )  before figuring out it was one)

Assuming he is with does of his species, he may be a little clumsy, or he may not have virile "swimmers" :)

Still, it is a risk. I do suggest he be taken out. He might figure it out, or grow into his virility.

On the other hand, if all the girls are house mice, that is the answer. House mice do not mate with field mice.

squeaks n giggles,

Natasha