Carter added that wildlife experts say culling a herd is an acceptable habitat management practice.
"In most cases, this animal is detrimental," Carter said. "He's past his prime."
But critics have questioned that logic. Officials from the Humane Society and the International Fund for Animal Welfare have said that while culling can be appropriate in abundant animal populations, all black rhinos should be protected, given their endangered status.
An estimated 4,000 black rhinos remain in the wild, down from 70,000 in the 1960s. Nearly 1,800 are in Namibia, according to the safari club.
Critics have also said any hunting of a rhino sends a bad message to the public.
"This auction is telling the world that an American will pay anything to kill their species," Jeffrey Flocken, North American regional director of the Massachusetts-based IFAW, said earlier this week. "This is, in fact, making a spectacle of killing an endangered species."
The auction was to take place Saturday night in downtown Dallas under tight security and behind closed doors. Organizers hoped to at least break the previous high bid for one of the permits in Namibia, which is $223,000, and had said the amount could be as high as $1 million. The winning bidder could come from anywhere in the world, and at least some bidders are expected to enter by phone.
Protesters were expected to rally against the auction Saturday.
Carter said he and Safari Club members were deluged in the days before the auction by angry messages, including the death threats.
"It appears to be an orchestrated series from people who are strongly anti-hunting," Carter said.
Poachers long have targeted all species of rhino, primarily for its horn, which is valuable on the international black market. Made of the protein keratin, the chief component in fingernails and hooves, the horn has been used in carvings and for medicinal purposes, mostly in Asia. The near-extinction of the species also has been attributed to habitat loss.
Graczyk reported from Houston.
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