A section of the Brook Waimarama Sanctuary fence that was cut out over the weekend ahead of a poison drop.

Holes cut in a Nelson bird sanctuary fence were among "acts of sabotage" ahead of a controversial poison drop, the sanctuary says.

A two-metre by one-metre section of the Brook Waimarama Sanctuary fence was cut out at the weekend and two sets of footprints were visible entering the enclosure, sanctuary general manager Hudson Dodd said.

He said the section was replaced and several smaller holes in the fence nearby were repaired on Sunday. But when workers turned up on Monday morning ahead of the planned start of the brodifacoum-laced bait drop they found "more sabotage".

MARION VAN DIJK A drop of brodifacoum-laced poison bait in the Brook Waimarama Sanctuary is designed to wipe out predators before native birds are reintroduced.

That included a security fence around the helicopter loading site being dismantled and thrown into bush, locks being added to sanctuary access gates, existing locks being glued and two pine trees being felled across an access track.

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Chainsaws were needed to cut up the trees for removal, and contractors and workers replaced the locks and re-erected the fence by 9am.

However, a logistical problem with the helicopter meant the drop eventually had to be postponed, Dodd said.

He said the sanctuary was "dismayed and shocked at the level of wilful damage and sabotage".

Police had been called when the holes in the fence were discovered, and were continuing to investigate. Officers had also spoken to a group of people who had parked cars across an access road on Monday morning before the drop was postponed, Dodd said.

The prospect of one or more people remaining in the sanctuary was concerning, he said.

Dodd said he understood the opposition to the use of brodifacoum, designed to wipe out predators in the 791-hectare sanctuary before native birds are reintroduced.

But he said the drop had been subject to rigorous consent and legal processes, including a "comprehensive" High Court judgement this month that rejected a bid by the Brook Valley Community Group to stop it.

"We believe we are doing it for the great benefit of the community and there is a huge amount of support for this project, so to have people take the law into their own hands is disappointing."

Dodd said the drop would proceed in the next suitable weather window after the sanctuary had given the required 48-hour notice to adjoining landowners.

Brook Valley Community Group chair Christopher St Johanser said he had repeatedly stressed publicly and privately that the group did not support or condone any illegal activity by "any person, at anytime, anywhere".

However, he believed it was understandable that people "may feel aggrieved at the position of the trust has taken and the manner in which the decision making about this drop has been managed".

St Johanser said allegations of sabotage were extremely serious, and had an "emotional loading" that was not supported by the facts.

He said the group was continuing to pursue its legal case and was hopeful it would get an urgent Court of Appeal hearing.