Waitākere Ranges rat numbers double, destroying endangered kōkako chicks and eggs

Wednesday, 20 November 2019

Kōkako nests in the Waitākere Ranges in West Auckland have been hit hard by rats after rodent populations in the area nearly doubled.

All of the kōkako chicks and eggs in three nests inside Forest & Bird's Ark in the Park have been destroyed by predators.

That comes despite being under volunteer surveillance and a 'ring of steel', which consists of traps every five metres.

Waitākere Forest & Bird branch chairperson Annalily van den Broeke said it was a 'tragic' start to the endangered bird's breeding season.

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'There are only about 60 kōkako in the Ark and 3600 left in New Zealand, so every loss is worrying.

'Somehow the rats slipped through.'

Rats doubled in number in the Ark between February and August, partly because this year was a 'mega mast' year and trees were producing exceptionally high amounts of seed, which boosted rodent numbers.

Numbers of stoats, weasels and possums were also believed to be higher, van den Broeke said.

In August, the number of rats in the park soared to record winter levels.

'We feel the heavy weight of responsibility as guardians of these kōkako, so to have this happen is an emotional blow [for us].

'Kōkako became extinct from the Waitākere Ranges about 50 years ago. We reintroduced them in 2009, but they're just hanging on and we don't want to lose them a second time,' van den Broeke said.

Rats, stoats and possums may have also taken a toll on the nests of many other native birds in the Ark, including threatened toutouwai/ North Island robins, van den Broeke said.

Three Forest & Bird staff members and about 400 volunteers carry out intensive predator trapping and rat baiting across the 2270 hectare Ark, which is a joint project between Forest & Bird and Auckland Council.

Despite 570 predator traps and 4800 rat bait stations, five out of eight kōkako nests spotted in 2018 were also ravaged by predators.

Only four kōkako chicks fledged in the Ark and its buffer zone last summer.

Hope remained that kōkako could have a second go at nesting this summer, van den Broeke said.

'One pair, the best producing father in the Ark, Maurice, and his unbanded mate are industriously building their second nest.'

Those who lived in the Waitākere Ranges could help the vulnerable native birds by putting traps or bat stations on their properties, van den Broeke said.

'Lots of neighbours already do their bit, but if everyone did predator control it would make a big difference.'