Jack W. Bradbury is a Robert G. Engel Professor of Ornithology, Emeritus at Cornell University. He undertook his undergraduate work at Reed College and received his Ph.D. in Animal Behavior from Rockefeller University. During his career, he has served on the faculty of Rockefeller University, the University of California at San Diego (UCSD), and Cornell University, as Associate Dean of Natural Sciences at UCSD, and, most recently, as Director of the Macaulay Library at the Cornell Lab of Ornithology. His research has included studies on determinants of dispersion, mating systems, and communication in a variety of taxa ranging from opisthobranch molluscs to various birds and mammals, with most work undertaken in the new world and African tropics. He has been teaching undergraduate courses in animal communication since 1970.Sandra L. Vehrencamp is Professor Emerita from Cornell University's Lab of Ornithology and Department of Neurobiology and Behavior. She received her B.A. with Honors from the University of California, Berkeley and her Ph.D. in Animal Behavior from Cornell University. Since 1976, she has served on the faculty of the University of California at San Diego and Cornell University. Her research has included field and theoretical studies of cooperative breeding, determinants of skew in reproductive success within social groups, the role of resource dispersion in shaping social structure, the role of energetic limits on display behavior in competitive mate attraction systems, and the evolution of song structure and vocal repertoire size in various songbirds. She too has traveled widely in both the Americas and the Old World tropics in pursuit of her studies, and focal taxa have included bats, antelopes, fiddler crabs, waterbugs, cuckoos, jays, grouse, parrots, wrens, and song sparrows. She has been teaching animal communication courses since 1986.