Your article "McCain: T.R. or W?" contains this statement: "The San Pedro hosts the second-most biologically diverse array of mammals in the world, second only to the Costa Rican cloud forests" (HCN, 9/1/08). As far as I know, no scientists have ever claimed that the San Pedro River had biodiversity second only to Costa Rica. Apparently what happened is that someone read an approximately 40-year-old scientific paper and completely misunderstood it. People liked to think there was incredible biodiversity along the San Pedro and in time the misconception probably became more and more incorrect.
Unfortunately, the incorrect statement about biodiversity has become widely believed and even crops up on government Web pages that provide general information about the San Pedro River. The consensus of scientists working on biodiversity has for about two centuries been that the greatest mammal biodiversity is in the tropics. EPA graphics showing the number of mammal species per water district suggest that the San Pedro River area has the same mammal biodiversity as found throughout much of Arizona and New Mexico.
Dr. Gary Noonan
Sierra Vista, Arizona