Knut, the Berlin Zoo's world-famous polar bear whose fragile psyche became an international obsession, died after several hundred visitors witnessed him falling in his enclosure.
The four-year-old was raised by zookeepers after being rejected by his mother. The cause of death has not yet been determined.
"It's terrible," Berlin Mayor Klaus Wowereit told a local paper, according to the Associated Press. "He had a special place in all of our hearts. He was the star of Berlin Zoo."
As a cub, Knut was known as "Knut the Cute." But later he became known as "Knut the Nut" -- a bear with serious psychological problems. His strange antics became a rallying cry for activists who believe it's cruel to confine a polar bear in a zoo.
A study by the German arm of People for the Ethical Treatment of Animals found that most polar bears in German zoos are insane -- and Knut was the worst of the lot.
The zoo said claims about Knut were overblown; in June, a spokesman called the statements "ridiculous" and maintained that "Knut is fine," according to AFP.
Knut, the four-year-old polar bear at the Berlin Zoo, has died. Once photographed with Leo DiCaprio for the cover of "Vanity Fair," Knut became world famous, though as he grew older, many said he showed signs of mental deterioration.
PETA said polar bears in zoos have one millionth the amount of space of those allowed to roam free and it's taking its toll.
"Some species fare worse in captivity than others and polar bears are certainly at the top of that list," Lisa Wathne, PETA's captive exotic animal specialist, told AOL News last year. "These animals are so severely restricted, it's literally driving them insane."
She pointed to a 2003 study in Nature magazine that found that animals with the ability to roam vast distances in the wild -- like polar bears -- do especially poorly in captivity.
Wathne, who was not involved in the Knut study, said bears in captivity also show bizarre behavior, such as incessant pacing and awkward twisting of the head and neck.
PETA scientist Frank Albrecht told AFP that Knut suffered from panic attacks, swayed in an abnormal manner and mimicked picture-taking tourists by pretending to snap photos with his paws. ...
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