Newly-released documents show a helicopter carrying out a 1080 poison drop near Lake Manapouri spilled some bait as it left its loading site.
Documents released to RNZ under the Official Information Act reveal the helicopter contracted by the Department of Conservation (DOC) deviated from its standard operating procedures during a drop near Te Anau in September.
According to DOC's incident report, the helicopter crew were under pressure to finish the drop due to bad weather, and pre-loaded the bait buckets before starting the aircraft, which was not usual practise.
A switch had been coincidentally activated, which allowed bait to fall from the bucket as the helicopter took off.
The report said DOC staff began a clean up straight away.
Te Anau resident Perrin Brown said he found pellets on conservation land, adjacent to the loading zone on private farm land on the day of the drop in September.
He said it took DOC several days to clean up.
DOC Te Anau operations manager Greg Lind acknowledged this, but said the spilled pellets were lying in inaccessible scrub land, not in an area used by the public.
DOC made several recommendations to the helicopter company that carried out the drop, including ensuring it did not deviate from its standard operating procedures for loading bait buckets.
Mr Lind said he was confident the company had learned from the mistake.
The contracted company did not want to comment, due to safety concerns for its staff.
The drop was part of DOC's nationwide war on pests known as the Battle for our Birds, which has been met with protests in affected communities, including Te Anau.