Future of tiny wren rests on rat control
A new South Island-wide survey has shown the future of a tiny, endangered mountain bird hinges on effective predator control.
The Department of Conservation (DOC) has released the latest findings from its rock wren monitoring programme, in which field researchers set out from Fiordland and work their way north to Nelson. They then walk or fly into 22 mountain sites and camp in alpine basins to survey rock wren, or tuke, populations over a few days.
There are two distinct populations of the birds, in the northern and southern parts of the South Island. The southern rock wren is considered endangered, while the northern rock wren is critically endangered.
Along with the rifleman, or titipounamu, rock wrens are the only New Zealand wrens left. Five other species are now extinct.
DOC research lead Tristan Rawlence said the results showed that tuke numbers were increasing at the 12 sites where predators were regularly controlled.
‘‘We’re seeing good numbers of rock wrens in areas where we’re keeping predators down using 1080 and traps, and they are trending upwards. In contrast, at the 10 sites where there is no predator control, numbers are low, and populations are continuing to decline or have locally disappeared.’’
Overall, Rawlence said, there were three times as many rock wrens in predator controlled areas versus unmanaged sites.
Rock wrens, which are found only in the South Island, were generally doing better in southern areas and west of the main divide, where there was less pressure from predators. In Westland, where podocarp and hardwood forests had fewer predators than beech forest, the birds had held out at unmanaged sites – but numbers were trending downwards.
Populations in Kahurangi National Park affected by the 2019 mega beech mast and resulting stoat plague have rebounded.
Rawlence said long-term monitoring was important to see how rock wren populations were responding to different predator control techniques, as well as the effects of climate change and other environmental factors.
As the climate warmed, predators such as rats would be better able to survive in once frigid alpine environments.
Tuke live year-round in the harsh alpine environment and are thought to hibernate for periods in winter. The birds are no bigger than a silvereye and nest on the ground – making them easy prey for rats and stoats.
The rock wren monitoring programme is part of DOC’s national predator control programme, which protects wildlife and forests across public conservation land.