Hihi’s last stand on Hauturu saved them from extinction, but could they soon be returned here? 

KATE WATERHOUSE 

Hihi translates as ray of sunlight, reflecting the distinctive yellow bands on the wings of male birds like the one shown here. It was photographed on Hauturu Little Barrier Island, the last refuge for this once widespread forest bird(1). Called stitchbird by early Europeans, named for its tzit tzit call, it is another of the lost species of Aotea. 

It is said that Hihi refused to fetch water for Maui after he had tamed the sun, so Maui threw Hihi aside and he landed in the fire, burning his feathers. The black and yellow is a permanent reminder of the lesson learned. Today Hihi still carries the sunlight through the forest(1). 

Early in the settlement of Tāmaki Makaurau, hihi could be found in Grafton Gully. In the 1860s, the ornithologist Sir Walter Buller noted that: 

A sudden disappearance from mainland forests 

When Buller returned six years later in 1874, he was astounded at how rapidly hihi had disappeared from the mainland. The last confirmed sighting was in the Tararua Ranges in 1883. It is miraculous that hihi are not extinct, as the huia was by the early part of the twentieth century. A combination of forest clearance and the introduction of mammalian predators was probably responsible for this catastrophic decline. By the late 1800s only one population remained, on the sanctuary island of Hauturu-o-Toi, Little Barrier. Just as tīeke survived on just one island, Taranga/the Hen, so hihi made their last stand on Hauturu(2). 

Hihi persisted there thanks to the diversity and quality of the island’s mature forest. But remember that hihi lived there in the presence of kiore and feral cats, strongly implicating the arboreal ship rat as the destroyer of all other hihi populations(2). One reason they were so vulnerable to predators on Aotea and the mainland is because they are cavity nesters – and they’re said to stay on the nest no matter what comes at them. Another reasons is that they are “mature forest specialists” – that is, they need a diversity of forest to thrive; and forest burning and clearance by European settlers destroyed most of their habitat. 

An important indicator species for restoration 

On Hauturu, hihi are a constant presence in the lower canopy, feeding on small flowering trees and nesting in cavities of old trees which may no longer be present in browsed, logged or burnt forests. This is the only hihi population that is natural and self-sustaining, so Te Hauturu-o-Toi provides a window into what hihi might have been like long ago. 

Hihi diets comprise a mix of fruit, nectar and insects/invertebrates—the proportions vary with availability and time of year. Their main food is nectar, but their diet spans more than twenty species of native flowers, thirty species of fruit and many species of introduced plants. Important nectar sources are haekaro, matata, pūriri, rata and toropapa, and they find these in abundance in the mid-canopy on Hauturu(3). This is also why translocated birds need to be fed – most forests don’t have what hihi need to survive the winter, and many have lost the old trees with cavities good for nesting. 

Hihi are important indicators of the health of New Zealand’s northern forests and are regarded as a benchmark for restoration site ecology due to their sensitivity to habitat quality. They thrive in complex habitats with high diversity of invertebrates, nectar producing plants and fruits – and there is very little of this type of forest left in New Zealand today. 

Aotea’s forests are infested with ship rats, but Rakitū is not. Thanks to the successful eradication project in 2019, the island is recovering. And the exciting thing for hihi lovers is that the original forest of Rakitū (the parts that cattle could never reach) is reported to be remarkably similar to Hauturu’s forests, which is after all only 20 km away. About a third of Rakitū’s 329-hectare area is still cloaked in such forest, an area larger than the whole of Tiritiri-Mātangi, and so are all but one of the other sites to which hihi have so far been translocated. It means it’s likely that Rakitū could once more sustain a population of hihi, without nest boxes and supplementary feeding. It is also likely that the remnant forested parts of Aotea could do the same, once feral cats and rodents are removed. 

Why is the return of hihi so significant? 

Most critically, hihi are no longer as genetically diverse as they were, and having all their eggs in the Hauturu basket puts them at risk of extinction should that population ever succumb to disease. Without hihi pollination some native plants have already been reduced to lower densities, it is uncertain what other roles hihi play in forest ecosystems(4). In 2022 research over 4 sites with translocated hihi showed plants produced similar quantities of fruit with or without hihi present(5). However, plants where hihi were present produced significantly higher quality seeds, suggesting hihi bring a unique pollination benefit. 

Managing translocated hihi populations is tricky and expensive, so the Hihi Conservation Charitable Trust works with the Hihi Recovery Group and DOC to monitor and manage them(6). As well as ensuring birds on Hauturu are protected, DOC’s Hihi Recovery Plan has a long-term goal of increasing the number of self-sustaining populations of hihi. The first birds were translocated to Karori Wildlife Sanctuary (now Zealandia) in the late 1980s, but hihi translocations to a number of island and mainland sites (see map) have not resulted in self-sustaining populations(4). Tragically the most recent one to Shakespear Regional Park failed in November 2021 after 17 months, following a stoat incursion(7). 

In 2021, seven reintroduced populations (including Shakespear) existed, totalling 600-800 birds, compared with ~ 2,000 birds on Hauturu. It is hard to say how many hihi are on Hauturu. A study of densities spanning 2005 to 20138 showed big variations over time, fluctuating between 4 per hectare and 0.8 per hectare. It is difficult to know whether these measure the true hihi population size or reflect other patterns of change we don’t yet understand. 

All of them have to be actively managed—with supplementary feeding and provision of nest boxes because of the lack of quality mature forest to support winter feeding and cavity nesting; as well as predator control, management of parasites, and population monitoring to avoid inbreeding and loss of genetic diversity. Aspergillus fumigatus, a fungus that grows in disturbed habitats such as those in regenerating bush is also believed to be a problem(2). This is why the possibility of an unmanaged population being safely established on Rakitū (and one day on Aotea) is so exciting. But consider also the significance of the return of hihi, a bird which was lost to the Aotea group around 150 years ago, to tangata whenua, and to the whole community of Aotea. 

A bird with character & its own species classification 

The male hihi is distinct with a flash of yellow shoulders and white crests on the side of his head which flick up and down when he’s excited, which he often is(9). The bright yellow male plumage is thought to come from carotenoids – pigments from native fruits which hihi eat, and which also contribute to egg yolks and overall health. Females are a less conspicuous brown colour but also with bold white wing bars. There is a distinctive shape to the tail when a hihi perches, although they are almost never still. Their distinct zip or “stitch” like call and high-pitched chatter are unlike any other bird. 

Hihi are one of Aotearoa’s “deep endemics” – birds that are only found here. They were at first classified as honeyeaters, along with tūī and bellbirds(3)(9). Their closest relatives were thought to be the Callaeidae, the family of perching passerines that include the now extinct huia, tīeke/saddleback and kōkako – which they don’t really resemble at all. But unlike them, hihi almost never come to the ground. Because of this and their other unique traits, they were recognised in 2007 as Notiomystis cincta, a new passerine family which contains only hihi(3)(9). 

Tower nesting and other hihi habits 

Hihi are unusual in their nesting habits, along with their social lives. On Hauturu nests have been observed between 2m and 40m off the ground, in natural holes in the trunks of trees such as pūriri, pukatea and taraire(3). Only one other honeyeater species in the world does this. Some researchers think that their cat-like whiskers may help them navigate the entrances. But here’s another surprise – hihi build a tower inside the cavity – between 20 and 40 cm above the height of the entrance. Up there is a deep woven cup lined with tree fern scales, moss, lichen, spider webs and feathers, on top of a stick base of 50 to 200 twigs. This is all built by the female and can take her up to 10 days – and she may try out several cavities before completing her nest. 

The male is in charge of finding potential sites, convincing the female that it’s a keeper by leading her to the entrances and dancing about, going in and out, sometimes even offering her nest building materials. Up to four clutches of 1-5 tiny white eggs (3 on average) can be laid in spring and summer. The female is really doing all the work at this point and may not start incubating the eggs until the clutch is nearly complete and the final egg is laid. She’ll spend about two weeks sitting on the eggs, which is a long time – about 2.5 times longer than other NZ bird species of the same size which makes her very vulnerable to predation. At birth, chicks weigh just 1 to 2 grams, and the female begins a feeding routine, rushing to and from the nest to keep them fed and growing, with only occasional help from the male. All this can be too much for her, and she may die or abandon the nest. Males have reportedly taken over the care of clutches when this happens, but the chicks likely perish. 

Sexually unique and socially gregarious hihi 

As well as being colourful, curious and charismatic, hihi have unusual social and sex lives, which is amongst the many reasons they’ve become a model species in conservation biology worldwide. 

Hihi enjoy a close social environment and overlap home ranges with their neighbours. A major benefit of this set up is that individuals learn by observing others – crucial for young learning to forage and develop survival skills from adults other than their parents10. DOC report that chicks from different nests get together after fledging and perform behaviours that could be interpreted as play; and adult males form groups with juveniles during the winter where hierarchies may be formed. 

Within this complex social structure is also a “variable” mating system, which involves multiple interactions between neighbouring males and females. Variable mating systems are unusual in any bird species, with only six other passerines worldwide thought to be polygynandrous (i.e. multiple male partners and multiple female partners). Researcher Isabel Castro’s work on hihi mating revealed a reproductive flexibility which means they can adjust the way they behave depending on the ratio of males to females, the availability of nesting and food resources and even the timing of breeding(2). 

A breeding group may consist of a pair, or one male tending to several females in his territory, or one female may have several males in attendance. Analysis of the genetic makeup of some clutches has shown that the male defending the nest may not necessarily be the father of all in that nest. One nest was found to have five eggs from four separate fathers, in a year where there was a near two-to-one ratio of males to females, so competition was very high. Females searching for food may also be aggressive to each other and when the population sex ratio is close to 50:50, a female may assist a male with territory defence. But once a female is nesting, the male may establish a second female in another nest in his territory later in the season. To cope with all this, male hihi testes produce a large amount of sperm and swell during breeding season to four times larger than expected by body size and to about 4% of their body mass, and bigger than the male’s brain. 

Finally, hihi are the only bird known to copulate face to face3. But not usually—most copulate with the male on the female’s back, and males compete with each other to do so. But sometimes, a typically unpaired male will harass and then force the female onto her back on the ground to copulate. On Tiritiri Mātangi, 34 (32%) of observed copulations were face-to-face, with only five being with the male partner of the female. While forced copulation is not unique to hihi, they are the only known bird species in the world where face-to-face mating occurs. 

What does the future hold for hihi? 

On Hauturu hihi still thrive unmolested by predators and in a forest which is still in balance. They occupy a niche that has all but disappeared from other forests. On Tiritiri-Matangi, hihi will not come down to a feeding station until the raucous tūī and bellbirds have had enough, and their breeding and food sources are closely managed by staff. Under intensive management like this hihi have been increasing in numbers at new sites, but they are still at risk of extinction. Introduced predators, disease, low genetic diversity and environmental disturbances like Cyclone Gabrielle continue to pose a risk to their stronghold. 

Ever present is the risk of a genetic bottleneck unless hihi populations increase. All hihi are descended from the group of birds that escaped extinction on Hauturu, which creates genetic risk, weakening hihi resistance to disease and other threats. Work by researchers at the University of Auckland showed that the risk of a bottleneck is real. They found three signs of low adaptive potential: a lack of diversity at the genomic level, low heritability in a range of adaptive traits, and lack of genetic variance in relative fitness(11)(12). This is the first time such extensive analysis has been done on a threatened species. 

They concluded that the only way for hihi to regain adaptive potential was for them to be supported to grow large populations which will then allow this process to occur naturally(13). Re-establishing a self-sustaining population of hihi on Rakitū will be an important step on that long journey. 

Kate Waterhouse is Chair of AGBET, member of Tū Mai Taonga Steering Committee & Deputy Chair of the Auckland Conservation Board. 

References:

1. Newsletter of the Hauturu Supporters Trust: https://www.hauturusupporters.org.nz/hihi-ray-of-light/ 

2. Taylor S (2001). A stich in time. NZ Geographic and the research of Isabel Castro: https://www.nzgeo.com/stories/a-stitch-in-time/ 

3. Wikipedia contributors, “Stitchbird” Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/wiki/Stitchbird 

4. Andrews CE, Anderson SH, van der Walt K, Thorogood R & Ewen JG (2022). Evaluating the success of functional restoration after reintroduction of a lost avian pollinator. Conservation Biology e13892. 

5. Hihi Conservation Trust 2021 and 2022 annual reports: https://www.hihiconservation.com/ 

6. Department of Conservation: https://www.doc.govt.nz/nature/native-animals/birds/birds-a-z/stitchbird/ 

7. Veale A (2022). Recent stoat incursions in the Hauraki Gulf. Environmental News, Issue 45, Summer 2022. https://www. gbiet.org/environmental-news/2022/2/25/environmental-news-issue-45-summer-2022 

8. Toy R, Greene TC, Greene BS, Warren A, Griffiths R (2018). Changes in density of hihi (Notiomystis cincta), tieke (Philesturnus rufusater) and tui (Prosthemadera novaeseelandiae) on Little Barrier Island (Te Hauturu-o-Toi), Hauraki Gulf, Auckland, 2005-2013. New Zealand Journal of Ecology 42. 

9. NZ Birds Online: https://nzbirdsonline.org.nz/species/stitchbird 

10. Franks VR, Ewen JG, McCready M & Thorogood R (2022). Foraging behaviour alters with social environment in a juvenile songbird. Proceedings of the Royal Society B: Biological Sciences. Tiritiri-Mātangi research: https://www.hihiconservation. com/research-publications/foraging-behaviour-alters-with-social-environment-in-a-juvenile-songbird/ 

11. De Villemereuil P, Rutschmann A, Lee KD, Ewen JG, Brekke P & Santure AW (2019) Little adaptive potential in a threatened passerine bird. Current Biology 25: 889-894. 

12. Bonnet et al. (2022). Genetic variance in fitness indicates rapid contemporary adaptive evolution in wild animals. Science 376: 1012-1016. 

13. Duntsch L, Tomotani BM, de Villemereuil P, Brekke P, Lee KD, Ewen JG & Santure AW. (2020). Polygenic basis for adaptive morphological variation in a threatened Aotearoa/New Zealand bird, the hihi (Notiomystis cincta). Proceedings of the Royal Society B: Biological Sciences. https://www.hihiconservation.com/research-publications/polygenic-basis-for-adaptive-morphological-variation-in-a-threatened-aotearoa-new-zealand-bird-the-hihi-notiomystis-cincta/