This Gambian epauleted fruit bat is typical of the exhibits in "Masters of the Night: The True Story of Bats," which just opened at the Field Museum in Chicago. The exhibition is to emphasize the positive roles bats play _ for instance, this flying fox will drop undigested seeds, helping to reforest parts of Africa. Among the displays: a colony of the little critters and an interactive "bat cave" that lets visitors use a joystick to maneuver a bat model using sonar to find food. The exhibition runs through Labor Day. For information, phone (312) 922-9410; the TDD number is (312) 9299.