According to an article in the Telegraph:
When a male mouse meets the object of his desire he sings her a love song, scientists have discovered.
It has long been known that male mice utter ultrasonic squeaks in the presence of the opposite sex, but a study using the latest computer analysis has established for the first time that these are more than mere random sounds - they are full-blooded love ballads. 
Trials with 45 different mice produced similar results, with each male singing a slightly different tune.
The team now wants to see whether the females are swayed by a good male song, which could be a measure of his fitness.