Good as gold
Operation Nest Egg, launched almost 10 years ago to try to boost the dwindling numbers of kiwi on the mainland, has proved to be a profitable investment in the future of our national bird.
From its drab exterior, the Native Fauna Centre at Auckland Zoo could easily be mistaken for one of the maintenance buildings alongside it. Inaccessible to the public—a strenuously steep hill sees to that the centre does not advertise the role it plays in ensuring the future of some of New Zealand’s most endangered species. I had come here to take a behind-the-scenes look at one particular initiative: Operation Nest Egg, part of Bank of New Zealand Kiwi Recovery.
Operation Nest Egg (ONE) began in 1994 in response to evidence that only five per cent of wild kiwi chicks survive the first six months of their lives. Research indicated that this mortality was due, in the main, to stoat predation. But it was found that while stoats have no trouble killing a chick, they are unable to pick off older, heavier birds. When they reach a kilogram in weight, kiwi are able to defend themselves against stoats. ONE was devised to enable them to reach this “safe weight.”
Department of Conservation kiwi researchers Rogan Colbourne and Hugh Robertson devised the strategy of taking kiwi eggs from the wild, incubating them until they hatched and then keeping the chicks in a predator-free “crèche”—typically an offshore island—until they reached the safe weight. (In all but one kiwi species, chicks fend for themselves from the moment they hatch.) They could then be relocated to the area they came from.
One was conceived with the Okarito brown kiwi in mind, but because its population was so low—estimated to be around 150 in the early 1990s—it was decided to trial ONE on the more common North Island brown.
To learn the details of kiwi egg incubation, Colbourne built an electronic egg containing temperature and motion sensors. Trials using this dummy egg in wild nests confirmed that kiwi, like most other birds, turn their eggs regularly. This piece of information alone resulted in improved hatch rates.
In another trial, to check that artificially incubated chicks could forage successfully, 10 kiwi chicks were released onto predator-free Motukawanui Island, in the Cavalli group. The chicks thrived, reaching the safe weight in around three months. A further trial, involving relocation of the juveniles from the crèche to their original collection area, was also successful.
All the indications were that ONE could help ailing kiwi populations, so four institutions Auckland Zoo, Rotorua’s Rainbow Springs, the Whangarei Bird Rescue Centre and Napier’s Westshore Nocturnal House were given the go-ahead to set up breeding units.
Todd Jenkinson, a member of Auckland Zoo’s Native Fauna Team, leads me into the centre’s incubation room. On the walls are charts and diagrams detailing kiwi gestation. A large poster shows all the developmental stages, from early embryo to hatchling.
On a bench are four large incubators, each containing a kiwi egg. The incubators are kept at a temperature of 35º C and a relative humidity of 55 per cent. The eggs are turned four times a day and removed from the incubators for an hour a day to cool down. These actions mimic natural rhythms in a wild kiwi burrow, such as the brooding adult going off to feed.
Eggs take between 75 and 80 days to hatch, and can arrive at the zoo at any time during that period. To assess an egg’s age, staff candle it—a simple process involving holding it to a strong light, thus silhouetting the embryo. Candling also reveals the size of the air sac, which increases as the growing embryo consumes the yolk, and is another useful indicator of the stage of egg development.
The hatching process begins with the egg jiggling around as the chick starts to move, following which the chick makes a tiny hole in the air sac with the tip of its bill, allowing it to breath air for the first time through the nostrils on either side. After this burst of activity, known as internal pipping, the chick rests for 12 to 48 hours.
The chick then pokes its bill through the shell before taking another rest. This is known as external pipping. Finally, pushing its large feet against the wall of the egg, the chick breaks away chunks of shell and muscles its way out.
Watching a kiwi hatch is an amazing experience. The chick makes squeaking noises as though pleading for help, but as tempting as it is to give assistance by picking away bits of shell, doing that could have disastrous results, says Jenkinson. Just inside the egg is a membrane containing blood vessels, and although this dries up as the chick hatches, the blood vessels could easily be ripped if forceps were used to assist in the “delivery.”
When the chick has fully hatched—a process that can take up to five days but is usually complete in three—it is weighed and placed in a brooder, again at a temperature of 35º C. Over the following two days the temperature is lowered to 20º C. By this time the chick has recovered its strength and started to explore its surroundings.
It is then put into a larger brooder, which has two compartments. One of these contains a layer of leaves and twigs for the chick to probe with its bill—a feeding action that comes naturally. The other, smaller compartment holds soft bedding material and is where the chick rests.
Zoo-hatched chicks are not fed for the first 10 days of their lives. Like chicks in the wild, they are sustained by their yolk. If fed, a chick might not absorb all of the yolk sac, which could then become infected and cause the chick to die from blood poisoning.
Every morning the chicks are weighed—the only contact staff have with them. Staff adhere to a strict “hands off” policy to ensure the chicks remain as wild as possible. Chicks lose about 25 per cent of their hatching weight during the 10-day fast, but quickly put on weight when they begin to be fed. If a chick loses 30 per cent, the team intervenes and starts feeding it. If 35 per cent is lost, a vet is brought in to ascertain the problem.
The chicks take three to four weeks to regain their hatching weight, and it is at this point that the zoo’s work is done. DOC staff take over, releasing the chicks onto their crèche islands.
A Kiwi called Horo is ready for his Big OE. I pick him up in his Auckland Zoo travel box and drive him to the DOC office in Warkworth. From there we take a boat to Motuora Island, in the Hauraki Gulf, with the island’s ranger, Adrian Dubbelman. He tells me a little about the island and why it has become a kiwi crèche.
“It’s close to the mainland, so it’s easily accessible, but too far for stoats or rats to swim to,” he says. Considering the island was farmed for over 150 years, “the fact it has remained predator-free is amazing,” he adds. There are still 50 cattle on the island but they are only there “to cut the grass.”
The island is in the process of being replanted in native forest. On our way up to the release site we pass through a nursery containing some 25,000 young trees and shrubs—the work of the Motuora Island Restoration Society.
As we deposit Horo in a burrow, Dubbelman says, “That’s 41 kiwi we now have on the island.” Since the time of my visit, though, the number has grown to nearly 70. The birds do extremely well on Motuora. Food is plentiful and there is no competition from rodents. Some birds have even started breeding, and, in the 2002/2003 breeding season, a third-generation ONE egg was laid—the grandfather was an ONE chick hatched in Auckland Zoo.
“The father was just under two years old and the mother was just under three, which is a lot younger [for breeding birds] than in the wild,” says Rogan Colbourne.
At the Bream Head kiwi crèche, near Whangarei, a male was found with a chick a week before his second birthday—the youngest kiwi known to have successfully hatched an egg. (In the North Island brown kiwi and little spotted kiwi only the males incubates the eggs.)
Clearly, ONE is working. Since the scheme began, some 300 chicks have been hatched, of which 230 have been released into the wild.
A One-raised chick has a 65 per cent chance of reaching maturity, compared with a 5 per cent chance for a chick hatched in the wild. ONE birds released back into the wild are breeding, and in sanctuaries where there is predator control kiwi populations are steady or increasing. In fact, kiwi are doing so well in Northland and Tongariro that the programme may be phased out in these areas. Meanwhile, the precarious population of Okarito brown kiwi has been boosted to some 200 birds.
Successful as it has been in improving chick survival, ONE by itself cannot save the kiwi on mainland New Zealand. Along with predator-control programmes, it buys time for kiwi while the longer-term task of habitat restoration proceeds, explains Kieron Goodwin, executive director of the Bank of New Zealand Kiwi Recovery Trust. A vital element in the re-establishment of kiwi in the wild is public awareness of the problems facing kiwi, says Goodwin, and to this end the trust supports a vigorous education programme.
Auckland Zoo, along with the three other ONE institutions, plays a role in promoting kiwi awareness. In the Kiwi House visitors can view kiwi as they would be seen in the wild, and the zoo offers a daily “nature encounter” talk, during which visitors are shown a tame ONE bird named Curly.
Curly is so named because both his feet were curled up when he hatched, physiotherapy and manipulation being needed several times a day to straighten them. One of Curly’s siblings had the same problem—implying that it was an inherited condition—but died. A decision was made not to release Curly into the wild and risk spreading the genetic deficiency.
This decision reflects the thinking by kiwi researchers about the bigger picture of kiwi recovery. It costs around $2000 to rear a kiwi from the time the egg is collected to the time the bird is returned to the wild. Such an investment would be pointless if equal emphasis were not being placed on securing safe kiwi habitats long-term.
But restoring habitats is complex. Hugh Robertson is currently researching what effect removing stoats has on an ecosystem. It is not a straightforward equation of “remove the predator and kiwi will thrive.” Says Robertson: “If you remove stoats it could allow rats to flourish, which are their main food. This in turn could have harmful effects, but could also benefit native species hounded by stoats.”
The whole purpose of Operation Nest Egg, says Rogan Colbourne, is to boost a threatened population quickly by putting a lot of young birds back into it, or starting a new population elsewhere.
Colbourne is hoping to start an ONE programme for the rare Haast tokoeka kiwi in the 2003/2004 breeding season. Mating occurs in June/July, with the first eggs appearing in August/September.
“All that is needed is for one, or ideally two, years’ worth of eggs to survive, and immediately the population will be stabilised,” he says.
In the breeding season just past only two Haast tokoeka chicks survived, the majority of the others being killed by stoats.
In Okarito, only two chicks survived in the 2002/2003 season, and only then thanks to a last-ditch rescue effort that saw them taken from the wild and released onto a crèche island in the Marlborough Sounds.
Stoats killed 13 of 14 monitored Okarito chicks, and the 14th one drowned. This demoralising result was despite DoC mounting one of the largest stoat-control operations ever attempted.
By no means is kiwi recovery a fait accompli. While the search continues for a silver bullet to deal with the predator problem, programmes such as ONE, raising one chick at a time, are helping keep the national bird alive and kicking on the mainland.