Tīeke/Saddleback Conservation - A Short History

TIM LOVEGROVE (Auckland Council)

The tīeke or saddleback (Philesturnus rufusater) is one of New Zealand’s ancient endemic species, which evolved in a land free of predatory mammals. The species has a fascinating conservation history as it was with the tīeke that the former Wildlife Service successfully pioneered island translocations to save threatened birds.

Tīeke used to be common on Aotea Great Barrier, and could one day be reintroduced - feral cats and ship rats would need to be removed or reduced to very low numbers to allow them to survive.

Disappearing bird species

In 1868, Captain Frederick Hutton visited Aotea and described the birds. Hutton visited at a time before the full impact of European colonisation. He listed many species now extinct on the island, including shore plover/ tuturuatu, falcon/kārearea, rifleman/ titipounamu, whitehead/pōpokatea, robin/ toutouwai, stitchbird/hihi, kōkako and tīeke.

Some of these species, including hihi and tīeke, disappeared soon after Hutton’s visit, and like the mainland, both were probably extinct on Aotea by 1900. Although tīeke were widespread on the mainland in the midnineteenth century, they were very rare by 1880. In the North Island, they had disappeared from many places even before stoats, ferrets and weasels were introduced in the 1880s.

Three important predatory mammals, cats, Norway rats and ship rats were already widespread. Cats and Norway rats established quite early in New Zealand, probably around the time of Cook’s voyages and the sealing and whaling days of the late 1700s to early 1800s. Norway rats were aboard Cook’s ships during his three voyages between 1769 and 1777.

Ship rats - Arboreal killers

The ship rat did not arrive until much later, reaching New Zealand in the 1850s to 60s. This was around the time that the ship rat replaced the Norway rat as the common shipboard rat. It has been suggested that steamships with their warmer engine rooms suited ship rats better. And once established in New Zealand, they spread quickly. The spread of ship rats coincided with the catastrophic declines of some of our most vulnerable birds such as bush wren, hihi, tīeke, huia and piopio.

Compared with the more terrestrial Norway rat, the ship rat is highly arboreal and almost all nests of forest birds are accessible to them. While Norway rats and feral cats would have made significant inroads into populations of some of these vulnerable birds before ship rats reached our shores, it was the ship rat that finished many of them off, aided later by mustelids, especially stoats.

First successful tīeke translocation

Taranga/Hen Island was the last place where North Island tīeke had survived after they became extinct on the mainland. Unsuccessful attempts had been made to establish populations on Kapiti and Hauturu in 1925 and Motumuka/Lady Alice Island in 1950. In January 1964, a party led by Don Merton successfully transferred 23 North Island tīeke from Taranga to nearby Whatupuke/Middle Chicken Island.

The Whatupuke transfer in 1964 was a milestone for inter-island translocations of threatened birds - this was the first time that synthetic mist nets and portable tape recorders were used. Johnny Kendrick, a Wildlife Service colleague in Don Merton’s party, made tape recordings of tīeke calls and rigged up a switch and speaker system to play sound from each side of the net, allowing the birds to be lured back and forth until they were caught.

These new tools streamlined the capture process, making it much easier to catch larger numbers of birds quickly. Earlier attempts had suffered because too few birds were caught and released.

In terms of species loss, the rat invasion of the Big South Cape Islands (see box above) was New Zealand’s most costly ecological disaster of the twentieth century. It was a microcosm of what probably happened on the mainland in the nineteenth century and alerted everyone to the danger invasive rats posed to vulnerable island ecosystems. From the mid-1960s, an active programme was undertaken to spread tīeke around as many suitable islands as possible, as an insurance against further rat invasions.

Taukihepa/Big south Cape Island - Ship Rat Invasion

An example of how ship rats can quickly devastate vulnerable island faunas happened in the mid -1960s when they reached the hitherto rat-free Big South Cape Islands off Stewart Island. Herbert Guthrie-Smith had described the abundant birdlife on a visit in the early years of the 20th century and his classic of New Zealand natural history Birdlife on Island and Shore published in 1925, contains the exquisite first-ever photographs of the South Island tiēke and the now-extinct Stead’s bush wren. Guthrie-Smith knew how vulnerable these precious island relics of pre-human New Zealand were to invasive rats, and at the time of his visit this was the last place where Stewart Island snipe and South Island tīeke survived. This Garden of Eden was plundered when stowaway ship rats invaded and swept across the islands in 1964-65.

Rescue Attempt

Word reached the Wildlife Service in autumn 1964 that rats had invaded the Big South Cape Islands. Knowing the damage that rats could wreak on fragile birdlife, a party led by Brian Bell was sent to investigate. Rats were already in plague numbers at the northern end of 900 ha Taukihepa/Big South Cape Island, but the southern end was less affected. When the catching party returned in August, the rats had reached the southern end. While half of the party checked nearby rat free islands for suitable release sites, the others built a rat-proof aviary and began catching as many tīeke, wrens and snipe as they could. It was late winter, days were short and cold and the weather in these southern latitudes stormy and very challenging, especially for making landings on exposed, rocky islands.

Tools from North Island tīeke translocations

New-found tools (see main article) used for translocations of North Island tīeke earlier that same year were quickly put to good use to rescue the Big South Cape tīeke, and 36 were captured with 21 and 15 respectively released on nearby Big Stage and Kaimohu Islands. This eleventh hour transfer averted almost certain extinction of the South Island tīeke. Sadly, due to difficulties of catching and captive feeding, along with weather delays, the transfer of wrens and snipe was much less successful. Just six wrens were caught and transferred to Kaimohu Island but attempts to transfer snipe failed. A few wrens survived on Kaimohu until 1972, but none was seen thereafter. Stead’s bush wren and Stewart Island snipe are now extinct.

Coexisting with kiore

From the mid-1960s onwards, tīeke were released on a number of northern islands. A series of experimental transfers to Kapiti Island also occurred between 1981 and 1983. Apart from Kapiti, which also had Norway rats and possums, when choosing suitable release islands, the main criteria were sufficient areas (usually over 80 ha) of coastal forest and no predatory mammals, apart from Polynesian rats or kiore.

The relict tīeke population on Taranga had apparently coexisted with kiore for centuries, and at the time, apart from Kapiti, all of the recipient islands for tīeke releases had populations of kiore.

Tīeke translocations pick up pace

The early transfers included 29 birds from Taranga to Red Mercury/Whakau (1966), 29 and 25 respectively to Cuvier/Repanga and Fanal/Motukino (1968). The releases on Red Mercury and Cuvier were spectacularly successful but the release on Fanal in the Mokohinau Group failed for unknown reasons.

By 1971 there were enough birds on Whatupuke for a transfer of 21 to neighbouring Motumuka/Lady Alice Island and in 1972, 24 birds were transferred from the flourishing population on Cuvier to Stanley/Kawhitihu in the Mercury group.

Then, over a three-year period from 1981-83, in the largest translocation attempted to date and using four source islands, Cuvier, Taranga and Motumuka and Whatupuke in the Chicken Group, 244 birds were transferred to Kapiti. This was followed by transfers of 16 and 12 birds from Taranga to Motukawanui Island in the Cavalli Group in 1983 and 1984, and then 50 birds to Hauturu and 24 to Tiritiri Matangi in 1984 along with another transfer to Fanal of 29 birds in 1985.

Three more transfers of 138 birds sourced from Cuvier and the Chickens followed in 1986, 1987 and 1988 to Hauturu, along with three more experimental transfers of 122 birds from Stanley to Kapiti in 1986, 1987 and 1988. More recent transfers have included Mokoia, Motuhora, Rangitoto/Motutapu, Motuihe and Rotoroa islands, and to several predator-fenced mainland sanctuaries, including Tāwharanui and Shakepear regional parks.

South Island tīeke transfers

During the same period, parallel transfers were undertaken of South Island tīeke from the productive populations on Big South and Kaimohu to nine islands, including seven Stewart Island outliers and two islands in the Marlborough Sounds.

The choice of release islands was more limited for the southern tīeke, as the population on Big South Cape had existed on islands free of all rats. The release on Inner Chetwode, where kiore occurred, failed, suggesting that Big South Cape tīeke could not coexist with this rat species. More recent transfers have been to several Fiordland and southern lake islands and Orokonui, a fenced mainland sanctuary.

Kapiti Island releases

In the experimental series of releases on Kapiti, the aim was to test whether tīeke could coexist with Norway rats as well as kiore. During the early to mid-ninetenth century observers at the time described tīeke as widespread, despite an assumed overlap with Norway rats, possibly since the arrival of Cook.

Kapiti at the time represented something of a biological relic of the early nineteenth century as it lacked ship rats. Although possums were present, mice, mustelids and feral cats were also absent.

An important point about Norway rats is that they are mainly terrestrial, unlike the highly arboreal ship rat. In the experimental releases to Kapiti it was thought that if plenty of tīeke were introduced, there might be selection for birds that habitually nested and roosted high, thus avoiding predation by Norway rats.

In 1981, shortly after the first release, I began a study of tīeke on Kapiti jointly funded by the Wildlife Service, and the Department of Lands and Survey, which administered the Kapiti Island Nature Reserve. My study proved to be especially instructive about the survival of tīeke in the presence of Norway rats. During the first 1981-82 summer, I found 24 survivors from the first release of 100 birds, and although one female was killed at a nest by a rat, that summer 22 young fledged. This gave strong grounds for optimism that tīeke might survive on Kapiti. However, despite the population being boosted by further releases of 94 birds in 1982 and 50 more in 1983, by November 1983 I found only 19 tīeke on Kapiti comprising 16 survivors from the 122 that were released and just 3 locally bred birds.

Rat predation on roosting birds

Even by the end of the first summer’s field work in 1981-82 it was clear that mortality on Kapiti was much higher than the northern islands where kiore was the only rat. In April 1983, I found the first evidence of rat predation upon roosting birds. Although we knew that females would be vulnerable to rat predation at nest holes, until then we had no evidence that roosting birds would also be particularly vulnerable.

Tīeke are unusual because they not only nest in cavities, but they also seek sheltered nighttime roosting places in tree holes, under epiphytes growing on rocky bluffs and under overhanging stream banks. On Kapiti, many of these roosts were on or near the ground. Thereafter, I tried to locate and monitor as many roosts as possible. I soon began to gather increasing evidence of rat kills at roosts, including sign that Norway rats were responsible. Roost predation explained the very high mortality on Kapiti - all birds were vulnerable every night of the year – it wasn’t just a case of females being vulnerable at nest holes during the breeding season. By 1986, just four tīeke remained on Kapiti. It was no surprise that these four survivors all roosted high in tall trees where they were out of reach of Norway rats. During the previous year I attempted rat control over about 40 ha on Kapiti using poison baits, but the concept of removing rats completely from this rugged 2,000 ha island was just a pipe dream. At the time rats, had only been successfully removed from a few very small islands.

If we couldn’t remove the rats, the observation of some birds roosting high got me thinking about how I could manipulate roosting behaviour by providing safe artificial roost sites. I had observed tīeke roosting and nesting inside the walls of the derelict WWII radar station buildings on Cuvier, so it seemed a roost box with features of these man-made roosts, which had a bottom entrance with a dark perch above, might be worth a try. In July 1984, with the help of volunteers, 100 roost boxes were erected on Tiritriri Matangi and Stanley Island - placed at about chest height on trees in secluded spots with some surrounding understorey.

The roost boxes were an immediate success and enabled a series of experimental releases on Kapiti from 1986-88 into habitat with hundreds of boxes. In these releases, three batches of 40 birds each were transferred to Kapiti annually, with each batch comprising 20 known roost-box users and 20 natural roost users. Following release, most of the habitual roost-box users continued to use boxes and their survival was significantly higher than the natural-roost users.

Tīeke roosting behaviour

An important aspect of tīeke roosting behaviour, which enhanced the value of the roost box project, is that adults show their newly fledged young where to roost, and thus many box users trained their young how to roost in roost boxes. It was clear that this learned roosting behaviour had the potential to spread through the population. Rat predation at natural roosts would create strong selection in favour of birds roosting in boxes out of reach of Norway rats.

I also provided nest boxes, which helped to reduce female losses at nests, although some continued to use vulnerable natural sites, where there were further losses to rats. I also found that the roost-learning process for young birds took time, and many young were preyed on at ground roosts before they had learned to use a roost box. Although the roost and nest box experiment greatly enhanced tīeke survival on Kapiti, modelling showed that there would still be a decline, but much more gradual than before, with the population eventually dying out after 50-75 years.

Removing rats from offshore islands

At about the same time as I was experimenting with the roost boxes on Kapiti, steady advances were being made in removing rats from larger islands. In 1986, the successful eradication of Norway rats from both Motuhora in the Bay of Plenty and Breaksea Island in Fiordland, both around 150 ha, was a breakthrough.

Just 10 years later in September 1996, an aerial drop of anticoagulant poison baits successfully eradicated all rats from Kapiti, and during the 1996-97 summer, ten surviving pairs of tīeke bred in rat -free habitat for the first time. These birds formed the nucleus of the thriving tiēke population on Kapiti today.

Cats and stoats also threaten tīeke

Historically, rats haven’t been the only threat for tīeke on islands. Cats exterminated tīeke on both Stephens and Cuvier after lighthouses were established in the late nineteenth century, and cats were almost certainly responsible for wiping out tīeke on Hauturu. Tīeke were abundant when Hutton visited Hauturu in the late 1860s but very rare at the time of Reischek’s visits in the 1880s.

Tīeke are also extremely vulnerable to stoats and translocations to Maud, Motukawanui and Moturoa Islands all failed after stoats invaded by swimming from the nearby mainland.

I recall Brian Bell telling me that when they were surveying Maud Island using tape recorded calls to find tīeke, a stoat appeared in response to the calls, alerting the team for the first time that stoats had reached Maud Island. Perhaps this stoat had learned to tune into tīeke calls to find an easy meal.

Recently, the tīeke population at predator-fenced Orokonui Sanctuary was wiped out by stoats that had gained access over the predator fence, and the population at Tāwharanui was reduced by over 60% after stoats invaded the fenced peninsula. The Tāwharanui population was possibly spared because mice and rabbits provided a source of alternative prey for the stoats. Tīeke spend a lot of time feeding on the ground, so they are especially vulnerable to stoats and cats.

Pest-free islands and sanctuaries

These examples highlight the extreme vulnerability of tīeke to introduced predatory mammals, the importance of pest-free islands and sanctuaries to their survival and more recently, the role of brave and innovative conservation management to expand their range and greatly increase their numbers.

Both species of tīeke are now secure, and flourishing populations on several islands are big enough to withstand regular harvesting to provide birds for further translocations.

Predator Free 2050

The country has set itself an aspirational goal in Predator Free 2050. With present techniques, and to prove that this is achievable, we will probably have to undertake this as a series of incremental steps. An obvious early step is removing predatory mammals from 28,000 ha on Aotea, a goal that can be achieved with current methods. Just imagine Aotea with tīeke, hihi, kokako, bellbird and other now-absent species joining kākā and tūī in the dawn chorus!