Waikato Wetland re-introduces rats

A Waikato wetland sanctuary is reintroducing rats to drive out birds fouling a prized lake. The move is a last resort to try to scare off half a million sparrows and starlings which roost around pest-free Lake Rotopiko.

National Wetland Trust executive officer Karen Denyer says the non-native birds poo so much they are changing the ecosystem and endangering the water quality.

The sanctuary is using bio control by introducing around 30 wild rats, known as shipwrecks, as a research trial. The goal is not to have the rats prey on the birds, but to disrupt the birds' habitat and discourage them from roosting there.

The Rotopiko Rat Trial is a managed trial which will closely monitor , with a known amount of rats being introduced and their movements and responses to the birds being closely monitored. Denyer assures that if the trial is successful, they will be able to easily remove the rats again, as they have done before.

Lake Rotopiko in Waikato. Image credit National Wetland Trust.

The ultimate goal of the trial is to protect the water quality of the nationally significant peat lake, which supports a healthy and diverse population of aquatic plants. Most other peat lakes in the Waikato region have lost their underwater plants due to declining water quality.

"It's a bit of an unusual approach, but it's definitely worth a shot," said Denyer. "We've tried everything else, and the bird population has just continued to grow and wreak havoc on the ecosystem and water quality. We hope that by reintroducing rats, we can disrupt the birds' habitat and discourage them from roosting there."

The sanctuary has implemented a trapping regime outside the fence to prevent the rats from escaping and causing problems in the surrounding areas. Denyer points out that these nearby areas already have rats.

Denyer stresses that this is a research trial and all precautions are being taken to ensure the safety of the surrounding areas and the success of the trial. "We're not just blindly releasing rats and hoping for the best," she said. "We're working with a scientist who has recently released a paper on the methods we're using and we're closely monitoring the rats' movements and responses to the birds."

The Trust believes the potential benefits outweigh the potential risks and if successful, the trial could provide a new and effective solution for managing bird populations and protecting the ecosystem and water quality of peat lakes.