Researchers have debunked a common claim that 1080 poison drops silence birdsong in New Zealand's pest-plagued forests.
Aerial drops of the contentious poison remain one of the Department of Conservation's most effective tools at beating back pest numbers in our wilderness, where an estimated 26 million native birds are killed each year.
Opponents of 1080 claim it kills the very bird species it was meant to protect, and while some birds like kea, robins and tomtits may sometimes be susceptible, the poison is far less toxic to birds than mammals.
Now, a just-published study has quashed the notion that large drops lead to mass bird die-offs.
Victoria University researchers Associate Professor Stephen Hartley, Roald Bomans and Asher Cook turned to bio-acoustic monitoring technology to investigate whether there was any difference in birdsong after operations.
After comparing recordings taken over weeks before and after drops in the Aorangi and Southern Remutaka Ranges with those captured in untreated sites nearby, they found little evidence of short-term effects on local native bird communities.
After the Aorangi operation, in 2014, the mean prevalence of birdsong increased slightly in treatment sites - while it remained at near-identical levels in non-treatment sites during the same period.
During another drop at Aorangi three years later, birdsong decreased in both treatment and non-treatment sites - but there was no evidence this was linked to 1080.
Meanwhile, following a Southern Remutaka operation, also in 2017, birdsong actually increased in treatment sites two to six weeks after 1080 was dropped - and decreased at the untreated sites.
In all cases, the researchers found, both increases and decreases were minor.
Of nine native bird species studied for specific impact, five showed no impact, three showed increases in birdsong after at least one operation.
However, they heard fewer calls from the chaffinch and tomtit, which they say could be due to random chance, or could mean the birds are eating 1080 pellets.
The researchers recommended more precautionary research into the effect of 1080 drops on tomtits.
The new study follows earlier insights shared by Bomans, who specially developed an algorithm to isolate particular bird calls - particularly moreporks - at the study sites, to find an overall positive effect.
"We know from previous work that most native New Zealand forest birds benefit in the years immediately following effective mammal control," Hartley said.
"This study confirmed that modern 1080 operations do not cause forests to go silent, and that few, if any, native birds are suffering short-term adverse effects.
"Regrettably, without appropriate control of introduced mammals, population declines and extinctions of Aotearoa's native and unique biodiversity will continue."
One University of Auckland study, published last week, suggested that achieving New Zealand's goal of wiping out possums, stoats and rats by 2050 wouldn't be possible without similarly controversial tools, such as genetic controls.
Almost 4000 of our known native species – among them kiwi, kākāpō and kōkako - are now threatened with extinction.
Statistics show the extinction risk has worsened for 86 species in the past 15 years - compared with the conservation status of just 26 species improving in the past 10 years.