This time, though, the attack was at his own Jane Goodall Institute Chimpanzee Eden in South Africa. And Cussons, host of the Animal Planet show "Escape to Chimp Eden," is without an explanation.
Cussons said Saturday he would have to wait until the severely injured victim, a University of Texas at San Antonio graduate student inspired by famed primatologist Jane Goodall to study chimps, was well enough to provide details about Thursday's attack.
It was the first such attack since Cussons, working with Goodall's renowned international institute, converted part of his family's game farm into the sanctuary in 2006.
"You can train for it, you can do your best to prepare," Cussons said. "But when it actually happens, it's shocking and traumatic for everyone."
Cussons, who was himself attacked by a chimp as he tried to pull it off Oberle, took the extreme step of firing into the air, scaring the animals away.
Oberle was bitten repeatedly and dragged for nearly a half mile. Cussons said one of the chimps was injured in the scuffle. No one else was hurt.
Male chimps can stand more than 5 feet tall and weigh about 154 pounds, according to the Jane Goodall institute. The two chimps that attacked Oberle were male.
As a researcher, Cussons said Oberle had been trained to ensure he understood how the animals might behave and knew to keep a safe distance. He said Oberle was given additional training before addressing the tour group.
Cussons said Oberle broke the rules by going through the first of two fences that separate humans from the chimps. The chimps then grabbed him and pulled him under the second fence, which is electrified. Cussons said it was unclear why Oberle had moved so close.
Mediclinic Nelspruit hospital said Saturday that Oberle, 26, remained in critical condition in intensive care.
Oberle's mother, Mary Flint, said Friday that her son knew the risks of working with chimps and would not want them blamed for the attack.
"He adored them," she said. "Since he was a little boy he just loved them, and I just have faith that ... when all is said and done, he's going to go right back into it."
The sanctuary has been closed to tourists since the attack, while government and police officials investigate. The Jane Goodall Institute South Africa is conducting its own investigation.
"Everyone at Chimp Eden is hurting," Cussons said, saying the thoughts of staff members were with Oberle and his family.
Cussons said the two chimps that attacked Oberle, Amadeus and Nikki, have been isolated since the attack. He said they were calm and exhibiting remorse, which he said chimps show by behaving submissively.
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