Is chirping mouse sick?

Question
My sons mouse "Pete" is almost 2 years old and has recently started making a chirping noise.  I have read different opinions on whether this be from happiness or sickness. Her (Yes I know Pete is a strange name for a girl) fur is soft and shiny, eyes bright, and she is very active still so I don't think it is illness. She seems to chirp louder when checking out new treats or being handled. I understand that she is an older mouse, but my son would be devastated if she was ill without us realizing (her sister passed away less than a month after we got them). Is is unusual for mice to make noises when they are not ill?

Answer
Dear Carin,

Take Pete to the vet. It is almost certain that she is sick. Because mice are prey animals, they don't show signs of illness until they are really sick. So they can look great and be quite ill. A mouse can look perfectly healthy one day, and be on her deathbed the next. So get an appointment asap. You don't have to go to emergency, though; just take her tomorrow.

She chirps louder when she gets excited, because she breathes harder.

I wish her the best. Mice recover very well with the right antibiotics.

Is Pete living alone? That's no good for a female mouse. Unless you are phasing out of mice entirely, mice should at least be in pairs. Three is best so when one dies, you have time to get another; and the mouse left, though bereft at the loss of one friend, is not alone and lonely. Moreover, a lonely mouse is much more likely to get ill and to get mites; a lonely and sad mouse, even worse.

Do wait till Pete gets well before adding someone, if you choose to do so. And, since she is old, she can only be put with a baby, so aggression is not an issue.

Squeaks,

Natasha