Daniel Klem Jr. is an American ornithologist, known for his pioneering research into the mortality of birds due to glass windows. He is Sarkis Acopian Professor of Ornithology and Conservation Biology at Muhlenberg College.Klem obtained his BSc at Wilkes University and his MSc at Hofstra University. He served in the US military served during the Vietnam War, and was awarded the Bronze Star Medal. He subsequently obtained his doctorate from Southern Illinois University.In his 1990 papers "Bird injuries, cause of death, and recuperation from collisions with windows" and "Collisions between birds and windows: mortality and prevention", he calculated that between 100 million and 1 billion birds are killed, annually, in the United States alone, by flying into windows.His research has influenced the design of buildings, not least the Niagara Falls State Park Observation Tower, on which he was a design consultant. He holds several US patents relating to windows design. He has also written about the birds of Armenia. He received an honorary doctorate from Wilkes University, where he is also a trustee.