ATLANTA -- A giraffe at Zoo Atlanta died Thursday night from unknown causes, zoo officials said.

Zoo Atlanta officials said Betunia, a 23-year-old female giraffe, had been at the zoo for more than 18 years.

While the exact cause of the animal's death is unknown, zoo veterinarians believe the death was age-related.

The life expectancy for a giraffe in captivity is between 25 and 28 years, officials said.

A necropsy will be performed, but the exact cause of death may not be determined.

Dr. Dwight Lawson of Zoo Atlanta said that Betunia was known for her gentle disposition and often participated in public feedings.

"Betunia was well-loved here at Zoo Atlanta for almost two decades," Lawson said. "Many Atlanta residents remember Betunia from their childhoods and will grieve along with the Zoo Atlanta staff who cared for Betunia in her old age."

Lisa Smith, curator of large mammals at Zoo Atlanta, said Betunia was a favorite around the zoo.

"She was one of Zoo Atlanta's sweetest, gentlest and most beloved animals," Smith said. "She will be sorely missed by everyone whose life she touched."

Zoo Atlanta acquired a 2-year-old male giraffe, Abu, in 2006 from the Buffalo Zoo.

Zoo officials said they are in the process of obtaining two young female giraffes as companions for Abu.