GRAND RAPIDS, Mich. (Michigan News Source) – The USDA is releasing its report about an incident at John Ball Zoo when a hippo attacked and killed an antelope.

The incident happened in May when the zoo was introducing Jahari, an adult male pygmy hippo, to Chopper, who was an adult antelope in a new multi-species habitat. Jahari charged at and killed Chopper due to what the USDA says was territorial aggression that was exhibited before the attack and a lack of individuals on site that had direct knowledge and experience of introducing pygmy hippos with other species.

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In addition, the hippo had “never been housed with any other species,” the report detailed.

The zoo says it has since updated its protocols and procedures for introducing animals and says they believe the incident was due to individual animal behavior.