For 25 years a small team of bird experts have flown into the Landsborough valley in South Westland most summers to count birds. It’s one of the Department of Conservation’s longest running monitoring projects.
DOC Principal Scientist Colin O’Donnell has been involved in this work from day one, joined by the same few counters who return each year. Together they have counted over 100,000 individual birds.
Some things haven’t changed over that time. They still fly in by helicopter and camp in small tents in the beech forest with a view of the Dechen Glacier. In the evening they sit on their folding chairs and cook on small camping stoves under a fly for shelter.
“If we’d known we’d be doing this for 25 years we might have set up a more permanent camp,” laughs Colin.
During the day, they do five-minute bird counts at 174 stations along lines through the forest. Each observer listens to and records all individual birds calling around them over five minutes. It requires top notch bird call identification skills (for more on this see: Bird counting in the Landsborough valley).
In 1998, when the monitoring began, its purpose was to measure how bird populations fared as DOC began managing introduced predators – first possums, then later rats and stoats.
Today this is still the aim – but much has been learnt over the past quarter of a century.
Fresh from university, Colin first surveyed mohua (or yellowhead) in South Westland in the mid-1980s, for the former Wildlife Service. He found very few birds – the first warnings that this species wasn’t doing well.
Later, studies confirmed stoats were preying on mohua and trapping made a difference. Further research using cameras on nests revealed rats were also a problem.
Mohua had hung on in the Landsborough, along with a good range of other native forest birds. It was a priority to try to protect them.
Colin says they first set out to measure the benefits of trapping over just 50 ha of forest.
“It’s something I’m most proud of – it was a proof of concept that worked – showing that we could increase breeding success of birds like mohua and save the breeding females from predation.”
“At first, we naively thought that trapping alone over the 50 km-long Landsborough valley would be enough to recover the birds. The first 1080 operation was to control possums, and we later learnt how effective this would be at controlling rats and stoats as well.
“We designed the bird monitoring to be repeatable and practical for such a large valley. The 174 monitoring points give us enough data to be able to detect change in bird populations.”
That first year just 14 mohua were heard; last November the number was 485.
Mohua is now the most common bird, as it once would have been throughout South Island forests before introduced predators invaded.
Over this time, seven other native bird species have also steadily increased in number – tūī, bellbird/korimako, brown creeper/pīpipi, rifleman/tītitipounamu, grey warbler/riroriro, fantail/pīwakawaka and yellow-crowned parakeet/kākāriki kōwhai.
Six other native species have stayed stable or only very slowly increased – kākā, kea, tomtit/ngirungiru, wood pigeon/kererū, New Zealand falcon/kārearea and shining cuckoo/pīpīwharauroa.
Just two native birds have declined – silvereye/tautou and long-tailed cuckoo/koekoeā, which migrates to the Pacific Islands each winter.
Silvereye may be being outcompeted by the larger and more aggressive honeyeaters, tūī and bellbird, which have dramatically increased. Long-tailed cuckoo rely on mohua and brown creeper to raise their young, so may have been affected by earlier declines in these species. They could also be impacted by conditions during their Pacific over-wintering. We don’t know for sure.
In total, native birdlife has more than doubled.
In contrast, introduced birds such as hedge sparrow, chaffinch, thrush and blackbird have declined, their fortunes reversed as competition for food and space has grown.
Overall, the results have been phenomenal, Colin says.
“It’s beyond what I imagined but not beyond what I hoped.
“When mohua became the most common bird in 2019, I thought, yes, we’ve done it!”
Over time, the counting has got more difficult with more birds and a chorus of overlapping calls.
The results of monitoring and knowledge gained have been used to adapt the predator control programme over the years. Now extensive trap lines snake for 56 km either side of the river, and aerial 1080 operations are carefully timed with the cyclic beech forest seeding or masts, which cause rat numbers to spike.
However, things are always changing in nature, especially with climate change and warmer temperatures favouring rats by allowing them to better survive over the winter months.
Ongoing monitoring is important, to detect future changes in birdlife and check predator control remains effective.
“In 2010, there was a year where we missed controlling rats after a beech mast, and we noticed a drop in mohua numbers. It took six years before they recovered to their former levels,” says Colin.
“If we detect a decline in some birds this could be the first early warning. If it was the start of a trend or pattern, we’d need to look at adapting our management.”
Over the years new bird counters have been trained but the original team is still going.
Colin says these days his knees get sore, but he still enjoys his annual trip into the valley.
“My dream day is just going off to have time by myself to count birds.”
Have a watch of the below video to see Colin and the bird count team in action and learn more about the Landsborough valley.