RUMFORD – A 4-inch-long brown bat found hibernating in a western Maine cave turns out to be 30 years old, and that’s an old-timer if you’re talking bat years.

Thirty years for a bat is the equivalent of 100 human years, according to Bat Conservation International of Austin, Texas. The oldest known bat caught in the wild was 34 years old at the time of recapture.

Two state wildlife biologists discovered the old bat hanging around with about 400 other hibernating bats last month in two abandoned mines in northern Oxford County.

Biologist Karen Morris consulted national experts who keep records on bat bandings and was told the Maine mammal was 30 years old.

“The bat was less than a year old when it was banded in August of 1971,” said Morris, who conducted her mine search with Heather Givens, another biologist with the state Department of Inland Fisheries and Wildlife.

Then Morris got a second surprise. It turned out her discovery was a bat from Maryland, not Farmington, where she suspected the band had been attached.

That presented something of a mystery because the banded bat is not among the species found in Maine that migrate south. Little brown bats usually don’t go more than a few hundred miles to hibernate.

Maine’s two most common bats are brown myotis and northern long-eared myotis, which have a wingspan of about 4 inches.

During their recent cave search, the biologists did not find examples of Maine’s biggest bat, the 5-inch hoary bat, which has a wingspan of 12 to 14 inches and can fit through a quarter-inch crack, according to Morris.

Big brown bats may find suitable conditions for hibernation in some buildings, but myotis rely on caves or old mines or stone structures, which provide more constant temperatures.

Bats spend the winter in a state of torpor which allows them to conserve energy which is stored as fat.

Morris said biologists still have a lot to learn about bats.

“It’s amazing how little we know about bats,” Morris said.