SEND IN THE RATS!
Ship rats are being sent in beyond the wire of a predator-proof fence to try to save a nationally important peat lake network at Ō haupō from the effects of up to half a million pooping birds.
The Department of Conservation acknowledges the move will seem ‘‘counterintuitive’’ to some, given the rats could threaten native copper skinks and spotless crake birds (pū weto) inside the 12 hectare fenced area.
But, after a ‘‘very challenging conversation’’ amongst agencies, DOC sees the introduction of up to 50 rats over three months during a trial as the best option for now to try to scare off the birds.
The trial’s main goal is to protect water quality and plants in the three interconnected Rotopiko lakes from the effects of bird poo.
‘‘It may seem counterintuitive but focusing on lake protection is the key at this point,’’ DOC’s Waikato operations manager, Tinaka Mearns, said in an interview yesterday.
The National Wetland Trust has been trying for years to find a way to drive off the massive flocks of roosting starlings, sparrows and pigeons which have found a haven in the rat-free area at Rotopiko since the fence was installed in 2013 around the site’s east lake. The problem is compounded by the fact that birds feed in local farming areas then come to the comparatively small fenced-off area, creating a very concentrated amount of droppings that run off into the lake.
Now the trust has got so
desperate it will do a controlled temporary reintroduction of ‘‘locally captured wild ship rats’’ at the site 20 minutes south of Hamilton. The trial starts this week.
It admits it is ‘‘an experimental method which will be closely managed and monitored’’.
The trust’s executive officer, Karen Denyer, said one of the key goals of sending in the rats was for them to climb the trees at night and scare the birds away.
‘‘We want them disturbed at nighttime when the rats are active.’’
Denyer said it had not been possible to guesstimate the actual effects on native wildlife of introducing rats but it was hoped the impact on the spotless crakes would be minimised by the fact that they like being in or near water and the ship rats don’t.
‘‘My sense is the crakes are fairly safe,’’ said Denyer.
Expert advice suggested the pest birds would not simply move en masse from the area to another location after rats are brought in.
‘‘We believe [the birds] will disperse
A tunnel that will be used to monitor the presence of rats in the area once they are introduced.
across the district to different sites, presumably back to where they roosted prior to the eradication of rats from within the reserve,’’ the trust said.
Asked what gave the trust confidence in the rats method, Denyer said ‘‘a lot of talking to experts’’, including bird behaviour scientists. She was not aware of this method being trialled anywhere else in the world.
Mearns said the agency supported the trial, as it viewed the health of the lakes as being of paramount importance. She also noted there were solid populations of skink and crake elsewhere.
Denyer said the pest birds were creating an unwanted nutrient loading in the lake estimated to be six times what could be expected normally. Monitoring will be undertaken by the trust and Wintec to see if the rats experiment is working and dispersing the birds.
At the end of the experiment, the rats are due to be removed by trapping.
‘‘However, if the operation is successful, rats may need to be periodically introduced as an ongoing pest bird management tool,’’ the trust said. ‘‘The stakeholders will continue to explore other methods if the rat operation does not successfully disperse the pest birds.’’
The trust said the lakes within the Rotopiko network were nationally important because they supported healthy and diverse populations of aquatic plants. Most other peat lakes in Waikato have lost their underwater plants due to declining water quality.