The facts of the missing rock wren

Rock wren are small, reclusive birds found in small pockets of the South Island's high country. Their limited flying ability and nesting on the ground makes them easy targets for predators such as rats and stoats.

Population: unknown

Classification: nationally endangered
Rock wren
New Zealand alpine rock wren
The facts of the missing rock wren: 
  • Following a 1080 operation in the Kahurangi National Park in November 2014, 30 of the 39 monitored rock wren in the Grange Range were sighted.
  • Several weeks later, following heavy snow fall, 14 rock wren were sighted
  • 25 rock wren are unaccounted for.
  • No rock wren have been found dead
  • There are still rock wren on Grange Ridge and 5 nests are being monitored by a conservation group.
  • The missing rock wren could be attributed to many potential scenarios.
  • In two other areas where rock wren are monitored, following heavy snow fall, some of the rock wren have died, these areas have not been treated with 1080 poison.
  • Rock wren eat insects, so it is unlikely they would be interested in 1080 bait as a food source.
  • With no clear picture to why the rock wren are missing, DOC has excluded alpine zones with rock wren populations from future 1080 drops until they know more. They will continue to assess the situation. 
  • Trapping stoats is not practical over large areas of difficult alpine terrain where rock wren live.

Update

  • In the Grange Range and Lake Aorere areas of Kahurangi National Park 85% of rock wren nests were successful compared to 30% in nearby areas that didn't have pest control. 
  • In these non-treated areas up to one third of adult females also went missing – probably preyed on by stoats. 
  • Results from other comparison sites without pest control in South Westland (Haast Range) and Fiordland (Lake Roe) were also poor with nesting success 17% and 20%, respectively.

What about the rock wren that went missing last spring?
There is still no clear evidence as to why rock wren being monitored in Kahurangi National Park went missing after unseasonable weather and snow and the pest control operation last spring. While some birds were probably lost to 1080, early counts indicate the high nesting success due to stoat control has already balanced this out with 61 birds estimated in the area after the operation was carried out compared with 49 birds before hand. The full effects of aerial 1080 pest control on rock wren won’t be known until the end of next summer when the birds have another chance of breeding with reduced stoat numbers. 


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