Kerry is working on projects aimed at conserving alpine biodiversity. This involves developing monitoring methods for species in the alpine zone – both the species at risk and the introduced predators that threaten their existence.
Rock wren are highly sensitive to predation during nesting because they often build their nests on the ground amongst rock piles and vegetation. At sites where there is no predator control, only 20 – 30% of rock wren nesting attempts are successful.
Kerry Weston holding rock wren
How to catch rock wren
Between October and May when research is possible above the tree line, locating and capturing rock wren is difficult and requires a bit of guile and cunning.
An audio recording of rock wren is played to attract the birds – it prompts them to investigate what stranger might have invaded their territory. The birds are then herded like sheep towards a mist net set up within their territory.
Rock wren are an indicator species
Weighing a rock wren after capture in a mist net
The condition of rock wren populations can tell us a lot about the health of their alpine environment. Rock wren are a nationally endangered species, only occurring in mountainous areas of the South Island.
We don't know what rock wren do during the winter when snow covers their entire landscape, but suspect that they may become sedentary beneath the snow or even go into torpor.
This makes them highly vulnerable to predators in their environment, such as mustelids which are very well adapted to alpine conditions.
Weta Deinacrida elegans
Kerry explains, “Given that rock wren are significantly impacted by predators, we can use them as an indicator of general ecosystem health above the tree line.
"For example, if rock wren are doing well, then we can infer that other species that are also highly sensitive to predation are also doing okay. Invertebrates like weta, alpine grasshoppers and beetles need protection and of course, alpine skinks and geckos would be easy prey for stoats.”
Managing predator numbers
Prolific seeding of native snow tussocks above the tree line may provide abundant food for mice, which in turn supports high numbers of stoats during heavy seed years.
Working out what drives predator numbers above the tree line seasonally, annually and geographically helps Kerry to develop best practice management tools to reverse declines in alpine biodiversity.
Above the bush line, where predators are controlled, rock wren are doing OK. It’s a case of working out the best ways to do that.