Kākā numbers are booming in Wellington but they do have an indiscriminate appetite for ripping off tree bark.

It's an ecological own goal – but one Wellingtonians may be happy to concede.

The growth in kākā numbers has cost the city about 20 trees, thanks to the birds' habit of stripping the bark from their trunks.

Wellington City Council is having to deal with the consequences as the native parrots have spread from the Zealandia sanctuary to the central city and Mt Victoria, the latest place where tree damage has been spotted.

ROSS GIBLIN/STUFF Oriental Bay's norfolk pines are reportedly being targeted by kākā.

But councillor Peter Gilberd, the natural environment portfolio leader, says it's a nice problem to have.

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"They do damage trees, but they bring a lot of joy and beauty to the city," he said.

ROSS GIBLIN/STUFF Some of the norfolk pines in Oriental Bay have denuded branches, possibly as a result of damage caused by kākā.

"I'm reminded the residents of early Wellington complained about the [noise of] whales in the harbour."

Kākā have ripped shreds from trees in Civic Square, and in Courtenay Place. Now there are reports of them targeting the norfolk pines along Oriental Parade.

The council's environment partnership leader, Tim Park, said about 20 trees around Wellington had been cut down due to kākā damage.

SUPPLIED Wellington city Peter Gilberd says kākā are a good problem to have.

Most of those were near Zealandia, but many other trees attacked by the birds had survived.

They had no nefarious intentions for the trees, he said. "They are a bit like bogans – they are a bit boisterous."

Kevin Squire, of Harbour City Tree Care, said there had been an increase in kākā damage to trees as the birds spread in a "halo effect" from Zealandia.

"They seem to enjoy ripping the guts out of things."

Their favourite type of bark seemed to be conifer trees, which was making the norfolk pines along Oriental Parade a prime target.

If branches were ring-barked – stripped around their circumference – it could lead to deterioration and potentially the death of a branch. Stripping bark generally was bad for any tree's health, he said.

The leader of the council's urban ecology team, Daniela Biaggio, said: "We know Wellingtonians love the rich native bird life in our city.

"Living with nature has its challenges, and we are learning how to share our beautiful city with these threatened parrots.

"It's a testament to our capital that the population of North Island kākā is recovering and they are becoming more common in Wellington."