Fun fact: It’s hard to tell gender in deer mice because males testes are not visible… UNLESS he smells a female around! Then they pop out like this…. However, I’ve noticed that deer mice will rarely breed in captivity. I’ve had it happen only a handful of times in the many years I’ve been doing this, isn’t that interesting? Nearly all of the mice who gave birth in my care were already pregnant when they arrived 🐀 | MouseTales