India, Oct. 17 -- An 11-year-old female hyena died at the Delhi Zoo on Thursday under "mysterious" circumstances, zoo officials said, stating a post-mortem examination will be conducted to ascertain the actual cause of death. The zoo is now left with only two hyenas, a male and a female.

The hyena was found lying in its den -- within the enclosure. The body was retrieved and sent to the zoo hospital, where it was discovered that she had already died. Typically, hyenas stay inside dens created in the enclosure area, but they feed on the backside of the enclosure -- where zoo staff serves food to them.

Delhi zoo director Sanjeet Kumar said the cause of death is still unknown. "The hyena, which was 11 years old, was found dead on Wednesday...