After earning his D.V.M. from Tufts University, Mark stayed on as a resident in zoo and wildlife medicine. Then, in 1988, he became a faculty member at Tufts, where he later served as Director of the Wildlife Clinic and was one of the founders of Tufts Center for Conservation Medicine.

Mark's professional interests include medicine and surgery in wildlife, aquatic birds, environmental health, and conservation biology. He has been researching mortality in loons since 1987 and is well-known for his work on lead poisoning in wildlife and public health.

Mark joined BRI in 2015 as senior consulting veterinarian.