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.