An Australian Zoo has dropped an ad campaign offering free visits to all "rangas" to highlight the plight of orangutans after sensitive redheads complained.

Last week, advertisements ran offering "free Zoo entry for all rangas" during the school holidays. "Ranga" — an abbreviation of orangutan — is a common nickname for redheads.

"We seem to be getting quite a bit of a negative reaction to that request," said Zoos SA's director of conservation programs Kevin Evans, The Adelaide Advertiser reported.

"People are possibly more sensitive about it than we thought," he said. "We have a campaign over the school holidays because of orangutans being an endangered species – and so are human redheads," Evans said. Less than 2 percent of humans have red hair.

"Because of the way people move around these days, the genes that carry redheads are breeding out to brunettes and blondes," Evans said. "Eventually it looks like they are going to be extinct as well."

The Adelaide zoo will continue to offer free entry to people with red hair for the next two weeks to raise awareness about orangutans being endangered in the wild.

The campaign is timed to coincide with the birthday of the Zoo's male orangutan, Pusung, and will include daily talks about the species. Dyed red hair will qualify for free entry and zoo staff will not seek proof that patrons are natural redheads.

"We're not actually checking tops and tails, or anything like that," Evans said.

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