My research focuses on the history of ideas about animals. I am the author of Savages and Beasts: The Birth of the Modern Zoo (Johns Hopkins University Press, 2002), a study of the origins of naturalistic displays in zoological gardens, and the editor of the collection Representing Animals (Indiana University Press, 2002). I am the General Editor of the book series Animalibus: Of Animals and Cultures for Penn State University Press. Twenty-two volumes have appeared in the series since 2012. In 2015, Elephant House, a collaboration with the photographer Dick Blau, appeared in the Animalibus series.
In November, 2021, Johns Hopkins published my new book, Elephant Trails: A History of Animals and Cultures. The book traces a history of elephant-human interaction and argues that since prehistoric times, elephants have been part of how we make sense of our world and our lives. In March, 2025, Johns Hopkins released a new, revised edition of Savages and Beasts: The Birth of the Modern Zoo. After more than 20 years, my ideas about zoos, Hagenbeck, and much else have changed and I enjoyed this opportunity to return to work I did at the beginning of my career.