Genuine long-term studies in New Zealand are uncommon and when they are based on consistent, standardised work they are highly valuable additions to our knowledge. They also provide the fuel for informed debate and subsequent decision-making.
Recently we have seen the results of 20 years of intensive professional monitoring in one of the jewels of the conservation estate — the Landsborough Valley which runs for 50km in South Westland temperate rainforest.
The data has the oddities that you expect from real monitoring; a strong trend but a couple of species going against the flow.
The good news is the overwhelming trend is a doubling of total native bird numbers. They have reversed predator-driven declines that by the early 90s saw the rare and beautiful yellowhead or mohua close to a local extinction.
The recovery coincides with two decades of consistent aerial 1080 applications. Mohua have bounced back from 14 birds to 338; great news for this diminutive bird which is celebrated on the current $100 note.
Happily, more common birds like the tuī, bellbird, brown creeper, rifleman, grey warbler and kākāriki also clocked up significant upward boosts.
As you'd expect with real data, other birds like kākā, fantail, tomtit and kereru haven't shown statistically significant improvement yet, and two native species, the silvereye and the migratory long-tailed cuckoo, have declined.
Silvereyes are common nationally and may have declined locally as longer-term natives have regained their former share of the forest resources. The cuckoos are migratory so there may have been problems in their winter homes or in the stormy weather they sometimes encounter on their migration.
The mention of 1080 and its association with another overall good news story will no doubt ruffle feathers among those who describe the helicopter applications as terrorism and threaten vandalism and harm to DOC employees.
Once again the scientific data is contradicting the virally spread anecdotes of people who repeat the myth of silent forests caused by 1080. For the time being, 1080 is the most cost-effective way to undo the damage humans have caused by introducing rats, stoats and possums.
The chemical in 1080 occurs naturally in some plants, including the tea we drink; it is organic and breaks down to a harmless salt and the same acetic acid that makes vinegar sour. The harmful dose for humans is quite high because as omnivores we have some tolerance to it. It is tragic if dogs scavenge poisoned possums but the operations are well-advertised.
The clear notification of pest control operations gives the anti-brigade a fresh opportunity to conduct their sometimes nasty campaigns of dire warnings but the birds are singing a different story.