Halo project sees 25 fold increase in tūī numbers

Friday, 9 August 2019

Tūī are taking over Hamilton with a 25-fold increase in counts of the native bird since 2004.

The lift is largely due to the Waikato Regional Council's Hamilton Halo project which was based around controlling rat and possum numbers in forestry remnants within a 20 kilometre radius of the city boundary within the known dispersal range of tui.

Waikato Regional Council biodiversity officer Andrew Thomas said tūī are now the third most common native bird in Hamilton City green areas (parkland and vegetated gullies) behind fan tail and the grey warbler and are now commonly seen by Hamiltonians.

'They are now breeding within the City boundary, with the numbers present in winter being only a little greater than in early summer. Population numbers seem to have recently levelled off or even dropped somewhat.

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'We don't know why this is the case, although it may be because the Hamilton tūī are becoming more of a resident population and predator control within the city is not as comprehensive during breeding seasons as it is out in the Halo bush blocks. It is too early to tell if this is a trend or merely a 'blip'.'

Council staff monitor 100 sites in Hamilton, which are checked every two years for the bird's presence. If staff hear tūī at the site, it is marked accordingly. 

In 2004, tūī were heard at three sites, peaking in 2016 with 75 and falling in 2018 with 45 tui heard.

Over the past two years, the council has also recorded sightings of bellbirds (korimako) and kererū (New Zealand pigeons) in biennial bird surveys undertaken by Maanaki Whenua Landcare Research. 

'We are hoping that this means their numbers are rising enough for them to show up in the sampling, but again it is too early to tell if this is a trend or a 'blip'.'

 Bellbirds and kererū had not responded as dramatically to the pest control programme as tūī. Thomas said they were unsure why this was the case.

'This could be as a result of their populations being very low to begin with and taking longer to recover or it is possible that the pest control regime used for Hamilton Halo is not as effective for bellbirds and kererū as it is for tūī. It is possible that there is a gender imbalance in the bellbird population.

Adult bellbirds are small enough to be taken by rats, but females might be being killed by predators more often than males. This is because it is only females that sit on the nest, incubating eggs and they are vulnerable to predators raiding the nest.

Recent sightings of the New Zealand falcon (kārearea) and kaka (forest parrot) by members of the public suggest these two native birds may also becoming more regular visitors to the city in the near future, Thomas said.

It was also important to improve the urban habitat for native birds. Tree fuchsia, puriri, kohekohe, hinau and fivefinger have been identified as key native food plants for tūī, bellbird and kererū, he said.

'Further planting of these trees in Hamilton gullies and backyards will provide a reliable food supply for these birds throughout the year.'

The Council also reviewed the project as it was 10 years old and sought advice from Maanaki Whenua Landcare Research about future objectives. From that review, the Council decided to concentrate on consolidating the gains made with tui and attempting to improve the situation for bellbird and kereru.

Reports of birds within Hamilton had decreased as people became more accustomed to seeing tūī.

'We still get reports of more unusual species. A bellbird has been recorded breeding in Tamahere in 2017 and sightings in the city have included a female seen in Hillcrest in the same year.'