(Courtesy of Reid Park Zoo)

Dresena came to the Reid Park Zoo in Tucson in 2001. She was 34 when she died.

(Courtesy of Reid Park Zoo)

Scientists fear that Malayan sun bears are endangered.

A rare, elderly bear has been euthanized at a Tucson Zoo. She was the oldest known Malayan sun bear in captivity.

Her name was Dresena and, at 34, she had long-since surpassed the median life expectancy for a female sun bear in captivity, which is 23. Specialists at the Reid Park Zoo chose to euthanize her after test results confirmed abnormalities in her brain.

Dresena came to Tucson in 2001. Due to declining eyesight, she spent much of her time off exhibit in recent years. But Zoo officials say her den remained a favorite of behind-the-scenes tours.

Sun bears are native to Southeast Asia and they’re the smallest members of the bear family. Scientists fear they’re endangered, but their remote habitat and shy personalities make it hard to collect much data.