Jay is grazed by a bat one summer evening and thus inspired to investigations which reveal that bats sleep in the daytime (and upside-down), are mammals (and what this means), use echoes to find their way (with a sketch of bouncing signals), are quick at catching insects, and ""come in many different kinds."" It's all clearly explained and attractively designed (though the pictures are mostly just decoration) for children too young to read Patricia Lauber's more substantial Bats, Wings in the Night (1968).