Multiple gunshots startled volunteers at Orokonui Ecosanctuary in Otago late on Monday, prompting a warning from police over the use of firearms.
Eleven volunteers were listening for kiwi and morepork at the sanctuary when they saw a spotlight, then heard gunshots about 10pm.
Ecosanctuary general manager Chris Baillie said the latest incident was not a "one-off" with spent cartridges found and gunshots heard around the area over the last month.
Volunteers were left a "little nervous" from the incident.
They did not feel they would be intentionally shot. Rather, they were fearful of an accident like, for example, when people thought they had a deer and it was actually someone's head torch or reflective tape.