SAN FRANCISCO (CBS/AP) — San Francisco Zoo veterinarians euthanized the 30-year-old female bison Friday.

The expected lifespan of bison is 25 years. Given her age, the zoo’s animal care staff had been closely monitoring the bison and saw that her mobility had rapidly declined and she could not lift herself.

Eight bison remain in the bison meadow on the western end of the park. They are descendants of a 1984 birthday present to former Mayor Dianne Feinstein from her husband, Richard Blum.

The city Recreation and Parks Department said small herds of bison have made the park their home since the 1890s.

(Copyright 2013 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)