Fresh and most likable nature essays, first seen in The New Yorker in different versions. Ackerman (A Natural History of the Senses, 1990, etc.) sits at dusk in Mexico at the mouth of a cave. In a moment, 20 million bats will rise and fly to their night's feeding. At her side is Merlin Turtle, founder of Bat Conservation International (""I could probably raise ten times as much money if I promised people I'd get rid of all the bats in their area...""). Ackerman jeeps across Texas's Big Bend with him as he photographs bats and speaks of such species as the tube-nosed fruit bat, whose elongated nostrils look like party favors. He explains how bats are essential in the life-histories of avocados, bananas, dates, figs, peaches, and tequila. Nevertheless, they are systematically exterminated; Australia's government, for example, has managed to kill 99% of their flying foxes (a large bat with a foxlike face). Ackerman next visits a gator farm in St. Augustine, where she helps determine the reptiles' sex by putting her finger in their cloaca--a cavity in which the sex organs lie. Discovering that females have a clitoris, she asks, ""Does this mean that they can have an orgasm?"" But nobody knows--she's reached the limits of science. Flying to Maul, she is the guest of Roger Payne, the world's most faithful recorder of humpback whale songs. From him she learns that there are 35 known singers, and that the music is quite complex at first listen, but becomes monotonous over a season: all whales sing the same song, which evolves slowly year to year. Ackerman's evocation of a whale song shows her agile descriptive power: ""Then a trumpeting sound...surged into a two-stage grunt...followed by a stuttering lawn mower that changed from a finger being drawn across a taut balloon, then a suite of basso groans and a badly oiled garden gate creaking open."" A choice treat for both nature lovers and general readers.