The zoo says Gertrude suffered from chronic kidney failure caused by old age. She was 46.
Gertrude came to the San Antonio Zoo in 1970. The zoo says she was one of the 11 oldest white rhinos in any zoo in the world.
Zoo director Steve McCusker tells WOAI-TV (http://bit.ly/10mEGqd ) that he remembers Gertrude having an easy disposition. McCusker says she was "one of the real pets of the institution."