A flock of kea spotted by DOC ranger Ian Cox in the Kahurangi National Park.

Ian Cox had stopped for lunch near Mt Owen in the Kahurangi National Park when he was surprised by a flock of 20 young kea.

He noticed three of the inquisitive birds at first, then more and more of them appeared, squawking, jumping around and doing backflips.

"They were whizzing around in the sky that quickly, wheeling around, that I couldn't actually get a good count on them.

Ian Cox Some of the large flock of kea Department of Conservation Motueka ranger Ian Cox encountered in the Kahurangi National Park.

"It's quite comical, they are quite clumsy when they do backflips."

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While flocking was a natural behaviour for kea, sightings of them had become less common.

ALDEN WILLIAMS/FAIRFAX NZ Kea on Avalanche Peak, Arthurs Pass. (file photo)

The Department of Conservation Motueka ranger was dropped off in the park by a helicopter, north of Mt Owen, to do animal control last week.

Cox said when he stopped to have lunch, several kea appeared. He then spotted a few more, and so it went on. Before long, there were at least 20 juvenile kea hanging around him.

"About three of them seemed to check me out first, they seemed to be the ringleaders as such, then the rest were back at a distance."

ALDEN WILLIAMS/FAIRFAX NZ A sign warns people not to feed kea.

He knew the birds were juveniles as they had yellow marking on their faces.

"Their behaviour sort of gave it away.

"They are little rascals when they are that age."

Cox said the birds followed him while he walked for several kilometres.

He had worked for DOC for 28 years and spent most of that time "out in the hills" but had only seen that many kea together once before.

"It's really uplifting to experience something like that.

"All the integrated pest control we do is making a bit of a difference."

Kea Conservation Trust chair Tamsin Orr-Walker said the sighting was very exciting, and while it was not often seen, flocking was something young kea did after they left the nest.

"The fledgings leave at around six months of age and they flock together until they form breeding pairs, that can be at about three or four years of age."

She said there had been a lot of predator control in the national park which had a positive effect on nesting success the following breeding season.

"Hopefully that is an indication of lower pest numbers in that last season around that area which would be fantastic."

In the past, there had been reports of flocks of up to 50 birds but Orr-Walker said it was less common to hear of flocks of that size.

"It is fantastic to hear that is still happening."

DOC scientist Josh Kemp has been involved in research monitoring kea nesting success in the Kahurangi National Park since 2009.

He said the kea were between one and four years old and would have fledged since aerial 1080 operations in the area in 2011, 2014 and 2016.

Research showed in the 2015 and 2016 breeding seasons, after aerial 1080 operations, on average 50 per cent of monitored nests produced young kea.

Between 2009 and 2014, only 2 per cent of kea nests successfully produced young in areas in the park without predator control.

It was important to keep kea safe by not feeding them or encouraging interaction with people and property.

Studies had shown kea that were fed regularly were more prone to interacting with pest control devices (including traps and poison baits) and had accidents with man-made objects like cars because they had become used to investigating novel objects.