Officials at the Detroit Zoo said they euthanized a 27-year-old female polar bear because she had terminal cancer. The bear, Barle, had extensive tumors in her abdomen, the Detroit Free Press reported Thursday. \"Since her rescue a decade ago, Barle has been a favorite of our staff and visitors,\" said Scott Carter, the zoo\'s chief life sciences officer. Barle had been rescued from a circus in Puerto Rico in 2002 and was brought to the Detroit Zoo where in 2004 she gave birth to her only offspring, Talini. The average life span of polar bears is 15 to 18 years in the wild and 25 to 35 years in zoos, the Detroit Zoo said in a release.