No Longer Lost Forever – The Mohua
Reintroduced over the past 14 years through a series of translocations, Canterbury’s inland valleys are again home to small populations of mohua (yellowhead), the sparrow-sized songsters with bright yellow heads and breasts that grace the $100 banknote, after fears they had been lost forever.
Once the most abundant and conspicuous bush bird of the South Island beech forests, cherished for their magnificent throaty trill, today, mohua are estimated to number less than 5,000 in isolated populations, occupying less than 25 per cent of their former haunts.
A taonga species for Ngāi Tahu, mohua (Mohua ochrocephala) belongs to the endemic family of New Zealand creepers, which also includes the brown creeper (M. novaezelandiae), and closely related whitehead (M. albicilla) found in the North Island. It only ever existed in the South Island and Stewart Island.
Arthur’s Pass and surrounding areas had previously been home to large numbers of mohua, but by the 1980s, they had mostly disappeared due to habitat loss and predation. Following a double beech mast (seeding) in 1999 and 2000, a predator plague all but wiped out any birds hanging on in Canterbury’s inland valleys. It also pushed the last mohua out of the Marlborough Sounds and caused population crashes in Otago, Southland and Fiordland.
The Department of Conservation (DOC) launched its Mohua Recovery Plan in 2002 with the aim of maintaining and enhancing mohua populations through their present range and beyond, by halting and reversing the degradation of the forest ecosystem.
By 2007, there were only a handful of mohua in Canterbury. Marion Rhodes, DOC Biodiversity Threats Advisor, who has been involved with studying and monitoring mohua for over a decade, says it became obvious that without help, localised extinction in Canterbury was inevitable.
Since the early 1990s, DOC had been establishing mohua populations on pest-free off-shore islands using translocations with success as an insurance policy just in case they were lost on the mainland. With fears the Canterbury population was on the verge of extinction, in 2008, it embarked on its first of many translocations back to the mainland. ‘The goal was to return mohua to the Canterbury valleys where it once thrived,’ says Marion.
The first translocation involved flying 20 birds from Breaksea Island to Hurunui River South Branch in the Lake Sumner Forest Park, followed by 21 birds from The Catlins the following year. Five years later, DOC returned 58 endangered mohua to the Hawdon Valley from Chalky Island in Fiordland, with a second release of 20 birds from the Landsborough Valley in 2017.
While the Hurunui River South Branch population took time to establish, it has now grown to more than 100 birds. ‘I love going into the South Branch and seeing flocks of them. It’s massively rewarding,’ says Marion. ‘It was really precarious for a number of years. It took a while for us to say yes, it had been successful. For the past two years, numbers have been pretty stable, but we hope this population will increase further.’
The Hawdon Valley is showing promise but it’s been slow to take off. Of the original 58 birds that were released, Marion and her monitoring team only found 24 a month later, and that had dropped to 16 after the winter. Of the 20 from the Landsborough, only four stuck around. ‘It’s had to build slowly from there. It’s still at pretty low numbers, hovering in the low forties, but we are ever hopeful,’ she says.
This March, DOC, with the support of the Mohua Charitable Trust and Rātā Foundation, released a further 41 mohua from pest-free Chalky Island in Fiordland in the Poulter Valley, which lies between the South Branch of Hurunui and the Hawdon Valley. It is the first time mohua have been heard in the Poulter Valley for more than 20 years.
‘We’re hoping that the new arrivals will settle in the Poulter and that any that disperse will join the established birds in the other valleys,’ says Marion. ‘Intensive predator control to protect the critically endangered kākāriki karaka (orange-fronted parakeet) that live in these valleys has also created favourable conditions for mohua. It’s really exciting. I am looking forward to next spring to see how they’ve got on.’
From detailed monitoring and research of key populations carried out around the South Island, it’s become increasingly clear that predation (from rats, stoats and possums) remains the greatest threat to mohua populations, she says.
‘In the Dart River valley more than 75 per cent were lost in a single season due to rats. The previous season I was surrounded by mohua. The next season I was struggling to find any. That was a big eye-opener for me. When there are more of them, they do better. With lower numbers, survival just gets harder.’
Mohua are insectivores (hunt insects), feeding predominantly in the upper understory and canopy of tall forests. They are about the same size as a sparrow, weighing between 25 and 32 grams. They forage in pairs, family groups or flocks, depending on the time of year. They nest and roost in holes in trees, sadly making them easy prey for predators. ‘Though the holes seem like good hiding places, the female can’t get away if a predator comes into the hole. You not only lose the eggs or chicks but the female bird also.’
Mohua also have long incubation and nestling periods (20 and 22 days) and nest later than other introduced passerines which also makes them more vulnerable to predation. The introduced vespulid wasp also competes with mohua for insects and honeydew, and it too may have contributed to the birds’ disappearance from beech honeydew forests in the northern South Island.
Given the right conditions though, with the factors that have caused its decline either eliminated or significantly reduced, mohua have the potential to thrive. For a threatened species, it has a relatively high reproduction rate, laying up to four eggs. Depending on the food availability, they can lay a second clutch once the first brood have successfully hatched and fledged, producing up to four or five offspring in a single season, explains Marion.
Aside from being one of the more beautifully coloured New Zealand native birds with a lovely song (they were known as bush canaries by the early settlers), mohua can also be quite long-lived. Marion recalled a bird that had been banded 14 years previously as an adult. ‘It’s not unheard of for them to live to more than 10 years of age.’
But like so many of our native species under threat, you can’t just leave them to it, she says. ‘Saving them from extinction is an ongoing project. Translocations are not a quick fix.’ While poisoning and trapping works – twice as many mohua survive in treated areas – eventually another mast year occurs, predators return and the costly cycle starts again.
Mohua are protected as part of DOC’s Tiakina Ngā Manu predator control programme.
