The Department of Conservation is significantly increasing its pest control measures in the lower South Island because of an expected explosion in rat numbers.
The department has set aside $500,000 for the coming year to undertake rat control in Hawdon Valley, Dart Valley, Eglington Valley and the Catlins.
Recent monitoring in the Catlins showed rat activity was six times above normal levels, the department says.
Spokesperson Richard Suggate says the rat population explosion is affecting native bird species, particularly the mohua or yellowhead and orange-fronted parakeets. It is also affecting and long-tailed and short-tailed bats.
"If we don't intervene we may actually lose those populations completely from some of those valleys," he says.
The department's rat control work will start in the Dart Valley later this month.