But the June operation, carried out by the Department of Conservation, also caused the death of one of the 20 rare whio which are monitored in the national park.
Taranaki Mounga project manager Sean Zieltjes said rat numbers dropped from 93 per cent to three per cent after the operation, while possums were down from 61 per cent to 10 per cent.
Ferrets and stoats were also killed after eating rat and possum carcasses.
"The project undertook aerial 1080 predator control over 31,000ha in Egmont National Park to reduce predator numbers and give threatened species such as whio and kiwi a chance to successfully breed and raise their young," Zieltjes said.
"The operation is part of a much larger multi-tool approach to predator control, which will one day allow the return of lost birds such as kākā and kōkako to the mounga."
Rats and possums were monitored before and after the operation using tracking tunnels and wax chew cards, he said.
The result was good for the next breeding season, he said.
DOC operations director Brigitte Meier said whio were monitored through the predator control operation after birds were discovered to have eaten 1080 cereal pellets in the last operation in 2016.
"Unfortunately, one of 20 whio we were monitoring died from 1080 poisoning," she said.
A second bird died from unknown causes, and a third bird was killed by a stoat, or ferret before the operation began.
Whio now total 200 in the park as a result of previous pest control operations.
It is thought whio had eaten 1080 pellets due to a poor food supply as a result of flooding in streams.
Meier said aerial 1080 predator control strongly improved whio nesting success and survival of young ducklings through to adulthood and previous operations in Egmont National Park in 2016 saw fledgling numbers increase from 23 to 58 in 2017-2018 breeding season.
There are estimated to be 3000 whio, or blue ducks nationwide.
Meier said a final predator control operation was completed in the Kaitake Range, where there are no whio, in late October.