An endangered gazelle at the Topeka Zoo is dead after beating its head against a gate until it broke its neck.

The Topeka Capital-Journal reports a zoo visitor saw the 5-year-old Addra gazelle running from corner to corner before charging the gate three times.

Zoo staff members ran to the scene but the gazelle, Raul, was already dead.

Zoo staffers described the animal’s behavior as puzzling. The city says in a news release the zoo will run a necropsy and pathology evaluation to learn what might have caused the incident.

The Addra gazelle is a critically endangered species, with only 500 left in the wild.

It’s the second rare gazelle to die at the zoo, where a 3-year-old Addra died of a sudden illness in December 2012.