GRAND RAPIDS, Mich. (WOOD) — A pygmy hippo attacked and killed a sitatunga, a medium-sized antelope, at John Ball Zoo.

In a release sent out Tuesday evening, the zoo said the attack happened during a controlled introduction between the hippo and a male sitatunga named Chopper. The two had visually been introduced throughout the last month in preparation for them to be in a new multi-species habitat together. Those meetings went well, the zoo said.

Trained animal staff brought Chopper in the hippo habitat for a controlled introduction when the pygmy hippo “suddenly attacked” the sitatunga, JBZ said. Zoo staff immediately separated the animals and the animal care team tried to resuscitate Chopper according to JBZ. They were unsuccessful.

“The Zoo has successfully introduced species many times, and our staff was thoroughly prepared for this introduction,” said zoo CEO Peter D’Arienzo. “This sad incident reminds us that despite enormous cautionary measures taken by Zoo staff over the last several weeks, the behavior of wild animals can be unpredictable.”

JBZ said Chopper was loved by all the staff who cared for him.

Pygmy hippos are new to the zoo this year.