This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While aerial 1080 drops sharply reduce numbers of rats and stoats, the predators—especially ship rats—can rebound to higher numbers within a few years. Studying 24 years of small-mammal tracking records across New Zealand's public conservation land, researchers found that the timing of these rebounds varies between regions.
For predator control to be effective, they say, repeat 1080 drops should be timed according to the local context and based on the animals being protected. In a second paper using the same data, they report that, because of large variations in rat numbers from year to year, it is not yet possible to tell whether rats have expanded their range because of climate change. This study, published in New Zealand Journal of Ecology, describes the effects of aerial 1080 predator-control operations on the abundance of ship rats, mice and mustelids across New Zealand forests, using more than 591,000 tracking-tunnel records collected from 1998 to 2022 across 13 conservation regions.
The data show that 1080 is highly effective at reducing numbers of ship rats and stoats in the 1–2 years following its use, consistent with studies showing improvements in nest, chick and overall survival of vulnerable species such as whio/blue duck, pīwakawaka/fantail, kiwi and kākā. Mouse tracking rates recovered early (within 6–12 months) but then decreased again as ship rat populations rebounded to higher levels than in unmanaged areas over the subsequent 2–3 years. The size of rat rebounds varied greatly by region, with much larger rebounds in warmer zones and northern regions with more diverse low-elevation forests than in cooler southern and eastern South Island regions.
The size of rat rebounds probably reflects the food surplus available to individuals that survive control operations. Stoat activity recovered more slowly than rodent tracking rates, with the longest durations of control in cooler and drier South Island regions. Unless predators can be locally eliminated, the work shows that indigenous species populations are likely to be protected by 1080 only if operations are repeated regularly at frequencies appropriate to protect the target species from its key predators in a particular geographic region.
For example, the findings of this study concur with other research showing that kākā populations in South Westland would grow if 1080 operations were undertaken every two or three years to prevent stoat recoveries. This study, published in New Zealand Journal of Ecology, models long-term patterns in ship rat, mouse and mustelid activity using more than two decades of tracking-tunnel data from conservation land across New Zealand. The authors investigated how rodent populations have increased or declined over time, how tracking rates vary among different locations, including warmer and cooler environments, and whether there is evidence that climate change is influencing long-term trends.
The study also explores differences between rat- and mouse-dominated pest outbreaks and how mustelid populations respond to changes in rodent abundance. There has been concern that ship rats are expanding into cooler, higher-elevation forests where low temperatures previously limited their presence, posing a risk to important refuges for threatened native bird and bat species. However, this study found no overall trend from 2006 to 2022, despite high-elevation rat population outbreaks in response to large mast seedfall events such as the 2019 "mega-mast." Because of the large interannual fluctuations, longer time series will be needed to detect any emerging trends.
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