In one of DOC’s longest studies, native birds were found to have more than doubled in number after more than over 20 years of sustained predator control in the Landsborough valley in South Westland.
Predator control began in the Landsborough valley in 1994 after the impact of predators on birdlife was observed. Since then DOC has done valley-wide trapping and seven aerial-1080 operations timed with increasing rodent levels.
The most recent three 1080 operations covering the entire valley were in:
- 2016, and
Watch our video to discover how we monitored these native birds
To measure the effects of pest control DOC scientists have tracked the birdlife in the valley since 1998. This research involves a team of bird call experts doing approximately 175 ‘five-minute bird counts’. Each spring at fixed points in the valley, the team complete and record their counts which provide an index of relative bird numbers.
The results show that native bird numbers have more than doubled since pest control began. Most of the 13 different native bird species monitored increased but some remained stable or decreased as outlined below.
Mohua up from 14 to 485 birds
One of the most threatened birds in the monitoring area, mohua (yellowhead) numbers have increased more than 35-fold since predator control began.
Total native bird numbers doubled over the more than 20-year study.
These species showed a steady increase:
- Brown creeper/pīpipi
- Grey warbler/riroriro
- Yellow-crowned parakeet/kākāriki
These were stable when they would have otherwise declined:
- Wood pigeon/kererū
These species are competing with species that are now recovering.
These species declined:
- Long-tailed cuckoo/koekoeā
Silvereye are being outcompeted for food by more aggressive nectar-eaters such as tuī. Long-tailed cuckoo migrate to the Pacific islands each winter and may be affected by conditions there. They also rely on mohua and brown creeper to raise their chicks.
Numbers of introduced birds have also decreased. This is probably due to greater competition from more native birds.