Photos: Frozen Zoo may hold hope for saving the northern white rhino

Senior Keeper Ken McCaffree tends to critically endangered Nola, a 40-year-old northern white rhino, at the San Diego Zoo Safari Park.  (Gina Ferazzi / Los Angeles Times)

A mother southern white rhino, middle, and young son follow a male up a grassy slope at the San Diego Zoo Safari Park.  (Gina Ferazzi / Los Angeles Times)

Dr. Barbara Durant, director of reproductive physiology, uses tweezers to grab a test tube filled with eggs taken from a monkey at the Frozen Zoo at the San Diego Zoo Conservation Research Institute.  (Gina Ferazzi / Los Angeles Times)

Female southern white rhinos rest under a shade tree at the San Diego Zoo Safari Park. No one is sure why southern white rhinos breed well in captivity but northern white rhinos do not.  (Gina Ferazzi / Los Angeles Times)

A southern white rhino grazes next to a dirt road giving visitors a close-up view at the San Diego Zoo Safari Park. The southern white rhino population is listed as threatened due to an increase in poaching.  (Gina Ferazzi / Los Angeles Times)

Thick eyelashes protect the eye of critically endangered Nola, a 40-year-old northern white rhino, at the San Diego Zoo Safari Park. She is one of only 5 northern white rhinos left in the world.   (Gina Ferazzi / Los Angeles Times)

Animal keeper Jennifer Minichino feeds 6-week old Chutti, a greater one-horned rhino, in the nursery area at the San Diego Zoo Safari Park. Chutti was taken from his mother after two weeks because he wasn’t gaining enough weight. The species is listed as endangered.  (Gina Ferazzi / Los Angeles Times)

Senior Keeper Ken McCaffree checks the toenails on critically endangered Nola, a 40-year-old northern white rhino, at the San Diego Zoo Safari Park.   (Gina Ferazzi / Los Angeles Times)