Both the remarkable comeback of Jacobs' subject and her well-pared reporting bring more than usual interest to this story of the cahow, ""a petrel that nests nowhere else on earth but Bermuda."" No one has ever seen cahows at sea, Jacobs tells us, but they are thought to gather and feed far out to the Northwest, returning to the islands in autumn to breed. A single chick is hatched in late winter and goes off to sea in late spring--but first, ""Every night for a week it Comes out and folds and unfolds its wings over and over again. It exercises them vigorously in some safe, sheltered area, like an aircraft warming up and testing all its controls before taking off."" When Columbus sailed from Spain, we learn, there were probably more than a million cahows on the islands, where they had flourished for haft a million years. Then so many were killed by hungry Spanish sailors, the sailors' hogs, and rats from English ships that not a cahow was seen after 1620. . . until 1906, when one specimen was found. Another turned up in 1935, still another in 1945, and soon after that a twelve-year-old Bermudian worked with American Museum scientists to find their breeding grounds on Bermuda's rocky eastern islets and protect them from further threats. The boy is now Bermuda's chief conservation officer and oversees about 100 Bermuda petrels on the protected islets. Their story makes for a readable and upbeat chapter in species conservation, with some dramatic passages and evocative pictures.