This latest addition to an always-intriguing series describes the work of Fernando Rosas, John Reynolds and Lucy Keith studying manatees in different parts of the world. Gentle, slow-moving vegetarians, these curious aquatic mammals are distant relatives of elephants and live in the Amazon, in Florida and nearby ocean waters and in West African rivers. The three different but similar species are all listed by the International Union for Conservation of Nature as extremely vulnerable to extinction. Florida’s protected manatees are a tourist attraction, easy to see in the clear waters of the Crystal River and in discharge zones of power plants, where they congregate for warmth in cold spells. The more mysterious manatees of Brazil and West Africa lurk in murky rivers and are sometimes killed and eaten. These three researchers track the animals in different ways, use biological techniques to learn more about their lives, work with people of the area toward protection and even, in Brazil, experiment with returning some to the wild from captivity. Like other books in this series, this is distinguished by clear, realistic explanations of scientific fieldwork and well-reproduced photographs, many taken by the author. The text, on the advanced side for the intended audience, is broken up by captioned photos, some mounted as snapshots. Overall, it lives up to the standards set by others in this stellar series. (maps, resources, glossary, author’s note, index) (Nonfiction. 10-14)