The life of a scientist in the Department of Conservation is worlds apart from the traditional stereotype of a lab-coat wearing academic hidden inside and away from the ‘real world’. DOC’s Threatened Species Ambassador Nicola Toki talks to alpine ecologist, Dr Kerry Weston. Kerry’s work takes her to the top of New Zealand’s peaks to try to unravel the mystery of the world’s most ancient species of wren, a vital indicator for the health of our high rise ecosystems.
Kerry has been leading research as part of our Alpine Biodiversity team to determine the impact of introduced predators on rock wren/tuke populations and to assess benefits of predator control.
After five years of high-altitude research by the hardy rock wren field teams, the results are in and predation by introduced mammals has been found to impact significantly on rock wren breeding success in three alpine sites in the South Island. Almost half of all failed nests (48%) were due to invasive mammals, primarily stoats but also house mice. There were also incidents of predation from a rat and a possum. No stoat predation occurred when predator control was established.
The importance of predation in alpine environments is not widely understood but is a key science challenge for the alpine research team. “While we have a good understanding of the threat that introduced mammals pose in environments such as offshore islands and forests, the importance of introduced predators in an alpine environment is not as well understood,” Kerry said.
“Climate change may create additional conservation challenges if invasive mammals move to higher altitudes as temperatures increase in the alpine environment over time.”
Rock wrens are the Sir Edmund Hillary of the New Zealand’s bird world, and are our only true alpine bird. They are closely related to riflemen and are members of an endemic group that once comprised at least seven species of largely ground-dwelling wrens. New Zealand wrens are thought to be the most ancient form of passerine birds in the world.
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.
The rock wren team monitored 140 nests between 2012 and 2017 in three different sites (in the Haast Range in Mt Aspiring National Park; the Homer Gertrude Cirque* in Fiordland National Park, and Lake Roe, Fiordland National Park). Two of the sites had predator control (DOC 150 and 200 predator traps), and the Lake Roe site had none.
Although rock wren appeared well-adapted to breeding in the extreme alpine conditions, the primary cause of nest failures was predation by invasive mammals. Breeding success of alpine rock wrens was improved substantially by predator trapping at both sites where it was implemented. Stoats were found in all three study sites. They are difficult to detect, particularly in alpine sites, though we know from camera footage that rock wren nests are frequently attacked by them. For more information, Kerry has co-authored a paper on the methods of detecting stoats at high altitudes.
Overall, rock wren nest survival ranged from 2-28% at sites without predator control and 47-67% at sites where predator control was in place.
Kerry explains, “Given that rock wren productivity can be increased with predator control, it is likely that other native alpine taxa vulnerable to the same threats would receive similar benefits. Future research involves testing this hypothesis across a range of taxonomic groups (e.g. alpine geckos, weta).”
“In this study, predator control involved only ground-based trapping, targeting mustelids and rats. However, the logistics of trapping at landscape-scale across alpine habitats are really challenging. Novel predator control techniques that can safely be applied at scale above the treeline are urgently required.”
For a closer look at the work of the rock wren team, check out Biodiversity Technical Advisor Jamie McAulay’s video of the monitoring team at Lake Roe – and what it’s like for the field staff to collect data on rock wren survival in a non-treatment site.
*The trapping at the Homer Gertrude site is part of the ‘Southland Section of the NZ Alpine Club Conservation Initiative’. The Southland Tramping Club, the Hokonui Tramping Club and the Fiordland Tramping and Outdoor Recreation club assist the SSNZAC project.