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Kōwhai Bush trapping protects rare birds

In Kōwhai Bush behind Kaikōura, predator trapping may rescue the largest population of native robins and riflemen in lowland Canterbury from localised extinction.

Environment Canterbury contributed $49,120 towards the first year of predator trapping and set-up costs. Support is likely to continue for another four years, including monitoring to assess how well bird numbers have responded to predator control.

University of Canterbury Professor Jim Briskie said numbers of South Island robins-toutouwai and riflemen-tītipounamu had fallen steadily since students first started monitoring nests in the reserve, 20 years ago. He is confident that 12 months of trapping will improve nesting success.

Excell Biosecurity Kaikōura workers have laid out 264 instant-kill traps, checked every second week. By the end of October, 175 bird-predators had been caught including 54 rats, 12 wild cats, 4 ferrets, 4 stoats, 3 possums and many hedgehogs.

Kaikōura mayor Winston Gray said he backed predator trapping in Kōwhai Bush, one of the last remaining lowland habitats for robins and riflemen. He hoped the community would find a way to continue this work for the birds’ long-term protection.

“It should be a normal thing to see New Zealand native birds, not a special occasion,” Professor Briskie said. “It would be a shame if the only place these birds survive is protected on islands where people can’t see them.”

Kōwhai Bush is a rare and precious remnant of native lowland bush which once covered most of Canterbury. As well as protecting Kaikōura from flooding, this 420-hectare River Protection Reserve, including 240 hectares in bush, is a refuge for native species that are increasingly rare in lowland Canterbury.

However, predation by stoats, ferrets, rats and feral cats caused robin numbers to drop from 80 pairs in the 1970s to about a dozen pairs today, 10% of their density on predator-free Motuara and Allports islands in the Marlborough Sounds. Riflemen were down to about 10 surviving pairs.

“It’d be easy for one cat to wipe them out in one hit,” said Professor Briskie. “Localised extinction is a worry.”

Building nesting boxes out of reach of rats and mice had improved rifleman survival. Eighty per cent of chicks raised in the boxes fledged compared with 25% in natural nests, but many were eaten by stoats, ferrets and feral cats after leaving the nest.

Robins and riflemen are vulnerable to predators because they instinctively freeze when threatened. The strategy worked well for native birds of prey such as falcons, but made them easy pickings for ground-based introduced stoats, ferrets, rats, cats and possums.

Doing better at Kōwhai Bush are one of the largest bellbird-korimako populations in Canterbury, brown creepers-pīpipi which are endemic to the South Island, grey warblers-kōriroriro and silvereyes-pihipihi. The forest is also home to tūī, kererū (New Zealand pigeons), a few pairs of kingfishers-kōtare and Australasian harriers-kāhu.

Other birds including blackbirds, chaffinch and song thrush are also thriving, at about 10 times the density in Kōwhai Bush as in their native Europe. They had adapted to introduced mammalian predators, abandoning their nests when threatened and often breeding again.

Kōwhai Bush robins are starting to adapt, becoming shyer than robins on protected islands and making alarm calls on seeing ground-based predators. However, their populations continue to decline.

Kaikōura Forest & Bird secretary Barry Dunnett said the trapping programme has its full support. A similar but smaller project he is involved with in the Waimangarara River Reserve, running off Mt Fyffe, brought the robin population from one pair to several pairs in 12 years.

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