Only found in the southern half of New Zealand, the mōhua nests in tree holes, making it highly vulnerable to predators like possums, stoats and rats.
A beautiful splash of bright yellow covers its head and breast while the rest of the body is brown with varying tinges of yellow and olive. The female is slightly less brightly coloured than the male. The mōhua is the bird featured on our $100 note.
They prefer to feed high in the trees although they will feed on the ground.
While the female is in sole charge of the lengthy process of incubation, after the chicks hatch both parents spend a comparatively long period of time caring for the chicks.
Yellowhead/mōhua calls vary around the South Island because yellowhead have strong dialects. Overall they are always distinctly "yellowhead" though.
Today, there are about 30 existing populations. They are divided into three groups – those east of the main divide, small scattered Fiordland populations, and Southland/Otago hill-country populations.
Mōhua have also been transferred to several offshore islands – Chetwode Islands in the Marlborough Sounds; Breaksea, Chalky and Anchor Islands in Fiordland; and Ulva Island in Paterson Inlet, Stewart Island.
The populations east of the main divide seem to have suffered the greatest declines. The previously strong population in the Eglinton Valley (in Fiordland) suffered a major collapse in 1999-2001, nearly to the point of local extinction.
This was mostly due to unusually high numbers of ship rats, which predated on adults and chicks. Ship rats are excellent climbers, taking not just chicks and eggs but also incubating females that are sitting in nest holes, high in trees with no escape route.
The decline of mōhua
As with virtually all of New Zealand's threatened birds, habitat destruction has been a major cause of decline and many of our forests are still threatened with either clear felling or modification by selective logging.
In the 1800s, the mōhua was one of the most abundant and conspicuous of our forest birds, now it is the most threatened of its genus, Mohoua, which also includes the whitehead and the brown creeper. Unlike the other two members of its genus, the mōhua has disappeared from large, relatively unchanged forests and is continuing to decline.
Once mōhua inhabited podocarp-hardwood forests (such as rimu, totara and miro). Now they are found only in beech forests with fertile soils where they can find plenty of food. When Europeans first arrived in New Zealand the species was still plentiful, but forest clearances and the introduction of new predators such as rats, stoats and possums all had a devastating effect on mōhua survival. By 1900, the bird was disappearing from many of its traditional areas.
Although the majority of forests where the mōhua live are protected, even within these areas populations are still declining due to predation, forest browsing by possums and deer, and competition with introduced birds. The introduced vespulid wasp also competes with mōhua for insects and honeydew and the wasp may have contributed to the bird's disappearance from beech honeydew forests in the northern South Island.
A predator plague in 2000 drove the last mōhua out of the Marlborough Sounds and caused population crashes in Canterbury, Otago, Southland and Fiordland.
Another predator plague caused by high levels of seed production ('beech mast') in 2014, put mōhua at risk again.
Battle for our Birds protects mōhua and other native species from predators
The ship rat population explosion was likely to have been caused by the occurrence of two beech masting seasons in a row, along with mild winter temperatures in between. This meant the rats had an abundant food supply, with no cold winter to bring numbers down before another bumper breeding season. Stoat control in the valley may also have reduced predation on the increasing rat population.
This double beech mast phenomenon also occurred in other eastern mōhua-populated valleys, causing the extinction of the Mount Stokes population, and major declines in the Hawdon, Hurunui and Dart populations.
Those populations in the Southland hill-country seem to be the most stable. These include the Blue Mountains, the Catlins forest and Rowallan/Longwoods forest (near Tuatapere). These forests did not experience the same heavy beech seeding, and so remain under less predation pressure from rats or stoats.
DOC has established a Yellowhead/mōhua Recovery Plan 2002-2012 (PDF, 427K).
Its goal is to maintain and enhance mōhua populations throughout their present range and beyond, by halting and reversing the degradation of the forest ecosystem.
The mōhua is still accessible to the public in South Island mainland forests and therefore, priority is being given to managing the birds within these forests, mainly through predator control. Such management will also assist other forest birds.
Checking a mōhua nest in the Catlins
The fortunes of a mōhua population in the Eglinton Valley, Southland have been closely followed for the past 10 years by departmental scientists to monitor whether stoat control efforts have benefited the birds. Related research is also going on in the Dart Valley, Otago.
Early results have proved that intensive trapping of predators does help the mōhua. This entails laying traps every 100 metres in a grid layout covering half-a-square kilometre. A new bait method being trialled is to use hen eggs laced with different poisons and laid in tunnels. The entrance is too small to allow the stoat to do anything but eat the egg inside the tunnel preventing poison being spread into the forest.
Additional stoat control work using traditional trapping methods is also carried out over the mōhua breeding season on the Milford Track, the Blue Mountains (near Tapanui), Rowallan Forest (Tuatapere), Mt Stokes, the Landsborough and Hurunui Valleys and the Catlins.
Monitoring shows that continuous stoat trapping and occasional use of biodegradable 1080 poison has boosted the population of endangered mōhua in the Landsborough Valley in South Westland. Elsewhere this unique little bird is completely defenceless against rats and stoats.
For a threatened species, mōhua have a relatively high reproductive rate. Each year they can lay up to four eggs and once these have hatched and fledged the pair can raise another brood. Therefore, if the factors that have caused its decline can be eliminated or reduced significantly, the mōhua has a good potential for recovery. mōhua have also bred in captivity at Orana Park in Christchurch.