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.
Mohua 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, chicks, and eggs.
Did you know?
The mohua is the bird featured on our $100 note.
The decline of mohua
Habitat destruction has been a major cause of decline.
In the 1800s, the mohua 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 mohua has disappeared from large, relatively unchanged forests and is continuing to decline.
With the arrival of Europeans came forest clearances and the introduction of new predators such as rats, stoats and possums. These all had a devastating effect on mohua survival. By 1900, the bird was disappearing from many of its traditional areas. Once mohua 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.
Although the majority of forests where the mohua 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 mohua for insects and honeydew and the wasp may have contributed to the bird's disappearance from beech honeydew forests in the northern South Island.
Predator plague and beech masting
The mohua nests in tree holes, making it highly vulnerable to predators like possums, stoats and rats.
A predator plague in 2000 drove the last mohua out of the Marlborough Sounds and caused population crashes in Canterbury, Otago, Southland and Fiordland. Predator plagues caused by high levels of seed production ('beech mast') put mohua at risk again in 2014 as well as 2016.
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 mohua-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/mohua Recovery Plan 2002-2012 (PDF, 427K).
Its goal is to maintain and enhance mohua populations throughout their present range and beyond, by halting and reversing the degradation of the forest ecosystem.
The mohua 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 mohua nest in the Catlins
The fortunes of a mohua 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 mohua. This involves laying traps every 100 m 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 mohua 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 mohua in the Landsborough Valley in South Westland. Elsewhere this unique little bird is completely defenceless against rats and stoats.
Mohua are being protected as part of our Battle for our Birds pest control programme.
For a threatened species, mohua 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 mohua has a good potential for recovery. mohua have also bred in captivity at Orana Park in Christchurch.
You can help
Help protect New Zealand's native birds
- Volunteer with DOC or other groups to control predators and restore bird habitats.
- Don’t throw rubbish into water ways or storm drains.
- Set traps for stoats or rats on your property. Get more information from your local DOC office.
- Put a bell on your cat's collar, feed it well, and keep it indoors at night.
- Plant a range of native plants that provide food year-round to encourage birds into your garden.
When visiting parks, beaches, rivers, and lakes
- Only take dogs to areas that allow them, and keep your dog under control.
- Prevent the spread of pests. Check your gear for mice and rats when visiting pest-free islands.
- Use available access ways to get to the beach. Stay out of fenced-off areas. Leave nesting birds alone.
- Get your dog trained in avian awareness, and help save forest birds like kiwi and weka.
- Follow the water care code. Keep water craft speed to 5 knots within 200 metres of the shore.