Rat plague strikes blow against kōkako eggs and chicks
Kōkako nests have been hard hit by rats at Forest & Bird’s Ark in the Park in the Waitakere Ranges.
Predators have destroyed all the chicks and eggs from three kōkako nests under volunteer surveillance in the reserve over the past two weeks, says Waitakere Forest & Bird branch chairperson Annalily van den Broeke.
“It’s a tragic start to the breeding season for the kōkako. There are only about 60 kōkako in the Ark and 3600 left in New Zealand, so every loss is worrying,” she says.
Two kōkako chicks and five eggs have been eaten, raising concerns for other chicks hatching and for adult birds, which are vulnerable when sitting on nests.
One nest had broken egg shells and rat droppings in it. Rat catches have suddenly increased over the past couple of weeks and some trapped rats have been eaten, possibly by other rats and mice.
Rats doubled in number in the Ark between February and August, partly because of the megamast – or heavy fruiting of native trees. Numbers of stoats, weasels and possums are also believed to be higher.
All three trees with kōkako nests were surrounded by a “ring of steel”, consisting of traps every five metres.
“But somehow rats slipped through.
“We feel the heavy weight of responsibility as guardians of these kōkako, so to have them predated is an emotional blow.
“Kōkako became extinct from the Waitakere Ranges about 50 years ago. We reintroduced them in 2009, but they’re just hanging on and we wouldn’t want to lose them a second time,” says Mrs van den Broeke.
Rats, stoats and possums may have taken a toll on the nests of many other native birds in the Ark, including threatened toutouwai/ North Island robins.
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 last year were also ravaged by predators. Only four kōkako chicks fledged in the Ark and its buffer zone last summer.
Hope remains that kōkako could have a second go at nesting this summer.
One pair - the best producing father in the Ark, Maurice, and his unbanded mate - are industriously building their second nest.
“We would love it if everyone who lives in the Waitakere Ranges put traps or bat stations on their properties.
“Lots of neighbours already do their bit, but if everyone did predator control it would make a big difference,” says Mrs van den Broeke.
The council and Forest & Bird are working together to maximise the effectiveness of pest control, says council biosecurity manager Phil Brown.