Tui are tucking into the tasty nectar of the pretty-in-pink Taiwan cherry tree across Northland.

But as attractive as they look, the trees pose an invasive risk to native bush and birds are partly responsible for their spread.

Taiwan cherry trees are in full bloom and tui are flocking to them to slurp the tasty nectar. The birds also help to spread the seeds into native bush and the resulting trees then outgrow the natives and take over.

A tree pictured in Mains Ave this week had 15 tui making a song and dance about the irresistible flowers but Don McKenzie, the Northland Regional Council's biosecurity senior programme manager, said they were a pest and Northlanders with Taiwan cherry should get rid of them to protect native bush.

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The variety was imported from east Asia in the 1960s as an ornamental species to brighten gardens in late winter, but it has become invasive and is visible - particularly at this time of year - in Northland, especially in and close to built-up areas.

Although it was illegal for people to sell, propagate or distribute Taiwan cherry in Northland, its seeds were still being widely spread by birds, he said.

Taiwan cherry seeds can be carried for many kilometres by birds and evidence of that can be seen in places such as Whangarei's Western Hills, especially as they start to flower.

Mr McKenzie said the tree only provided nectar for tui for two to three weeks of the year when flowering and was a successful invader producing thousands of seeds attractive to birds. "The species can dominate road margins and bush edges as well as occupying canopy gaps in mature forest.

"Taiwan cherry may be colourful but it's really displacing the tui's natural nectar and fruit producing natives - flax, mahoe, kowhai, puriri, kowhai, and pohutukawa.

"The continual spread of these trees will actually harm the tui population as they lose more of their original habitat. In order to attract birds ... plant pohutukawa, flax, kowhai and ngaio."