Research from a predator control operation on Rakiura/Stewart Island to protect pukunui/southern New Zealand dotterel from extinction has provided valuable insights into the impact of 1080 bait on the island's non-target white tailed deer.
The study found Rakiura white-tailed deer are more susceptible to eating a lethal dose of 1080 bait pellets than other deer populations in New Zealand, and the use of deer repellent slightly reduced the impact.
The study was done by the Bioeconomy Science Institute (formerly Manaaki Whenua – Landcare Research) during an aerial predator control operation in August last year to protect pukunui/Southern New Zealand dotterel from extinction.
The operation successfully reduced feral cats, rats and possums to very low levels across approximately 40,000 hectares of Rakiura National Park. The operational area included 4 of the 35 bookable hunting blocks on Rakiura.
The study was commissioned by Predator Free Rakiura in consultation with stakeholders, including experienced local hunters and national hunting groups to help inform future operations targeting feral cats, rats and possums on the island. White-tailed deer are not a target species for the project, and, prior to this study, there was limited research on the Rakiura herd.
Bait pellets containing deer repellent were used in the hunting blocks, while standard 1080 bait pellets were used elsewhere in the operational area. A network of 242 movement-activated trail cameras monitored deer before, during and after the predator control operation.
The report found there was on average a 75 per cent reduction in deer detections by cameras in the deer repellent area in contrast with a 97 per cent reduction in the wider operational area where standard 1080 bait pellets were used.
These reductions in deer activity are higher than have been observed in some deer monitoring studies elsewhere in the country. The report outlines some likely causes, including low natural food availability, meaning the deer were hungry and more likely to eat the bait pellets, and the small size of white-tailed deer making them more susceptible to eating a lethal dose of 1080.
Another probable factor is a lack of herd exposure to 1080 bait pellets previously, meaning the Rakiura white-tailed deer were less cautious of the baits than in areas where there have been multiple 1080 predator control operations.
Department of Conservation Director Biodiversity National Programmes Ben Reddiex says this is valuable research that is being discussed with the Rakiura community and national stakeholders.
"It was expected that there would be some by-kill of white-tailed deer as they are known to sometimes eat 1080 bait pellets, but it was unclear what the extent would be.
"The impact was higher than anticipated, however the large majority of the Rakiura white-tailed deer population was unaffected, and deer will gradually re-enter and repopulate the operational area.
"There has been robust engagement with hunters, hunting groups and other stakeholders, and this will continue as we work towards implementing Predator Free Rakiura."
The president of the Rakiura Whitetail Trust, Adam Fairmaid, says this research shows a big challenge for Predator Free Rakiura going forward.
"Unfortunately, the operation resulted in a high mortality rate of white-tailed deer in the study area. Our bottom line is that we need a viable whitetail population on Rakiura. The Department of Conservation has assured us that they will work with us to find a solution."
It is estimated that white-tailed deer will be widespread throughout the operational area in low numbers within one year, and back to pre-operational levels in three-four years. This is based on other studies of population recovery for white-tailed deer and red deer.
Ben Reddiex says Rakiura still has a widely distributed population of white-tailed deer.
"This is shown by the consistent deer detections in the adjacent monitoring area where 1080 wasn't used, and the deer detected by cameras at the edge of the operational boundary."
DOC will monitor white-tailed deer as they move back into the operational area, using an existing network of trail cameras that is also monitoring feral cats.
Meanwhile, with feral cats, rats and possums reduced to very low levels in the operational area, pukunui have been able to have a successful breeding season on the Rakiura mountain tops.
"We've counted 37 chicks and 80 eggs across 36 nests which is a huge result as the population was down to 105 birds last year, largely due to predation by feral cats.
"We won't know the total pukunui population change until April when the team does the annual flock count, but all signs are pointing to a vital population boost for a species on the brink of extinction."
There are no aerial 1080 predator control operations planned on Rakiura in 2026 following the successful predator control operation, and while Predator Free Rakiura considers the next steps for the project following a predator eradication trial last year.
