ST. LOUIS - Songbirds may be the Sinatras of the animal world, but male mice can carry a tune too, say Washington University researchers who were surprised by what they heard.

Scientists have known for decades that male lab mice produce high-frequency sounds — undetectable by human ears — when they pick up the scent of a female mouse. This high-pitched babble is presumably for courtship, although scientists are not certain.

"It soon became ... apparent that these vocalizations were not random twitterings but songs," said researcher Timothy Holy. "There was a pattern to them. They sounded a lot like bird songs."

If the analysis by the researchers is confirmed, mice can be added to the short list of creatures that sing in the presence of the opposite sex, including songbirds, humpback whales, porpoises, insects and, possibly, bats.