The uncle of an American graduate student mauled by chimpanzees at a South African sanctuary says the man's parents are flying from the U.S. to visit their critically injured son.

Carl Oberle of suburban St. Louis said his 26-year-old nephew, Andrew F. Oberle, remained hospitalized Saturday.

Officials say the University of Texas at San Antonio anthropology graduate student was badly injured Thursday when two chimpanzees pulled him under a fence while he was giving a lecture at the Jane Goodall Institute Chimpanzee Eden.

Carl Oberle described chimps as his nephew's "passion" and says he knew each animal by its "name and face."

A conservationist who runs the sanctuary says investigators will have to wait until Oberle is well enough to provide details to try to determine what prompted the attack.