Four male Hamadryas baboons have been euthanised at Wellington Zoo, after their hierarchy broke down and they began fighting.
The animals were put down this morning, after efforts to rehome them weren't successful.
Since their hierarchy had broken down the baboons had been constantly fighting and injuring each other. Two had died in the past two weeks, the zoo's chief executive Karen Fifield said.
"What we had to decide was do we allow these animals to go to their death in a very violent way, because we know this would continue to happen, or do we decide that a very humane euthanasia in a peaceful and calm manner, is the best option for them."
The zoo had been through an extensive process of looking for other options for the males - including looking across the Australasian breeding programme to find a home, but there was nowhere for them to go.
The animals could not live on their own, as that would be equally distressing for the social animals.
Removing a baboon would not have helped either, as without the hierarchy, they would have kept fighting and eventually killed each other.
Euthanising the remaining four baboons meant the zoo did not have any left, which was extremely sad.
"They are pretty amazing animals... they are very engaging and they would engage with our visitors, and the keepers obviously think the world of them."
It hard been hard for the keepers to put the animal's welfare at the heart of the decision to put them down.
The zoo would not get more baboons, as it was reviewing its species plan for the next 20-30 years, and considering what animals met the criteria around conservation and advocacy.