One of the last remaining northern white rhinoceros was found dead late last week, according to a statement from the conservancy that held him.

Staffers from Kenya’s Ol Pejeta Conservancy found the rhino — one of only two breeding males and one of four residing at the conservancy — dead of unknown causes at the age of 34. The rhino, named Suni, died in his “boma,” or enclosure, and was not a victim of poaching.

The conservancy noted that the Kenya Wildlife Service would conduct a post mortem as soon as possible to determine the cause of death. The statement noted that his father died just eight years before in the Dvůr Králové Zoo, which is located in the Czech Republic.

With Suni’s death, there are just six northern white rhinos left in the world, and Suni was one of only two breeding males. Northern white rhinos have not been able to survive in the wild and thus all remaining known animals are in enclosures like the conservancy.

The conservancy pledged to “do what we can” to keep the three remaining animals healthy in hopes of successfully birthing a northern white rhino calf.

There are only three other northern white rhinos in the world outside of the conservancy.

The northern white rhino — also referred to as the northern square-lipped rhinoceros — is one of two subspecies of the white rhinoceros. Its cousin, the southern white rhinoceros, is much more plentiful in numbers and is found in the wild in southern Africa.