January 1946) is an American ornithologist, specializing in the neotropics.
He is the co-author of three books on neotropical ornithology: the field guide The Birds of Panama (with John Gwynne), The Birds of Ecuador (with Paul Greenfield), and The Birds of South America (with Guy Tudor), of which two monumental volumes (out of four), covering the passerines, have appeared.
He was long affiliated with the Academy of Natural Sciences in Philadelphia, then Vice-President at the American Bird Conservancy until 2006.
In 2001 he was awarded the Linnaean Society of New York's Eisenmann Medal.
In 2006, he received the Chandler Robbins Award from the American Birding Association.
He currently serves as president of Rainforest Trust and is one of the founders of the conservation NGO Fundación de Conservación Jocotoco, which owns and manages ten nature reserves in Ecuador.