Kiwis Saving Kiwis
by Tim Stoddard
Stumbling through a dense, moonlit forest, a man blows three shrill notes on a plastic sheep-dog whistle and pauses to catch his breath. Out of the inky silence, footfalls accompanied by loud sniffling noises encircle him.
The man crouches, his heart rate skyrocketing, and gives one last blow on the whistle. Infuriated by the noise, the unseen creature charges toward him, crashing through the underbrush like a raging bull elephant. Sound like the script of a low-budget horror movie? Wait. In the next scene, a foot-tall brown bird explodes through the bushes and skids to a halt next to the man, ready to rip open his unprotected shins with razor sharp claws. But the conservation officer expertly throws a handnet over the bird and scoops up Boris, a brown kiwi acting typically territorial in his home on New Zealands South Island. Its time for Boris annual radio transmitter change and a quick physical examination.
Named for the sound of their raucous calls, which the sheep-dog whistle so rudely imitates, kiwis are the beloved icons and national emblem of New Zealand. These quirky birds have long graced New Zealand currency and stamps, currently appearing, for instance, on the gold $1 coin. New Zealanders even call themselves Kiwis, a name that originated in the nations regimental badges and then became synonymous with New Zealand soldiers fighting abroad during the First World War. This recognition was further promoted by the logo of Kiwi Shoe Polish, which, following its creation in Australia in 1906 (by a man with a wife native to New Zealand), was marketed around the world.
Ironically, as kiwi-adoration has grown, the population sizes of New Zealands four kiwi species have been declining at an alarming rate, due to habitat destruction and the introduction of predatory mammals.Conservationists struggling to save these bizarre birds wonder whether future generations of "Kiwis" will know their namesakes only as images on currency and shoe-polish tins.
There are four recognized species of kiwis, with six subspecies distributed across the North and South Islands: the brown kiwi (Apteryx mantelli), divided into the North Island and Okarito subspecies; the great spotted kiwi (A. haastii); the little spotted kiwi (A. owenii); and the tokoeka (A. australis), divided into the Haast and southern subspecies. (Some scientists suspect that the subspecies merit status as separate species; DNA analyses now underway should clarify this.) [Editor's note: As of 2006, there are now considered to be five kiwi species: the great spotted, little spottled, North Island brown kiwi, rowi (formerly the Okarito brown kiwi subspecies), and tokoeka, which has two to four subspecies.]
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"Meet-A-Kiwi" Demonstration at the National
Zoo's Bird House |
All of the kiwis are pear-shaped, flightless, mostly nocturnal birds, but each species is a variation on the theme. For example, they vary in size from three to nine pounds and in height from 18 to 36 inches. Their plumage ranges from a uniform brown or gray in the brown kiwis to a spotted or barred appearance in other species. While kiwis are notorious for their bold, aggressive behavior toward anything or anyone who invades their territory, little spotted kiwis, the smallest and most endangered of the kiwi family, have a fairly mellow nature.
Kiwis possess some of the most bizarre, un-birdlike adaptations within the class Aves. Kiwis have traded keen eyesightthey are unable to see more than six feet in the darkfor acute aural and olfactory perception. Unlike those of any other bird, the kiwis nostrils are located at the tip of their seven-inch-long flexible bills, which they use to probe through leaf litter and soil as they sniff for earthworms, grubs, and other invertebrates that make up most of their diet. In proportion to the size of their brains, the kiwis olfactory bulbsthe cerebral regions that coordinate the sense of smellare the second largest recorded among birds, after petrels. In addition to these bloodhound noses, kiwis ears are well developed. Cocking their heads toward the ground, kiwis can locate the whispering sounds of tiny arthropods deep in the humus.
Kiwi feathers lack the interlocking structures that "zip" feather barbules together in most birds, so their plumage has a spiky, fur-like appearance. (Chinese gooseberries are also called kiwi fruits for the furry texture of their skin.) At the base of their bill, long, modified feathers called rictal bristles protrude like whiskers, giving the birds a well-developed sense of touch that helps them navigate around obstacles on moonless nights. Completely tailless, with tiny stubs of vestigial wings hidden beneath their plumage (kiwis belong, appropriately, to the family Apterygidae, which literally means "wingless"), kiwis run through the forest on muscular legs that account for over a third of their body weight. With a nocturnal lifestyle and burrowing habits to boot, some scientists jokingly refer to kiwis as honorary mammals.
Kiwi reproduction is stranger still. A female little spotted kiwi is burdened by an egg that is by far the largest relative to body size among birds, growing to 26 percent of her body weight, while the eggs of other kiwis average 15 to 20 percent of a females weight. According to standard ratios of body mass to egg weight, kiwis, being about chicken-sized, should lay chicken-sized eggs. Instead, the bird generates a super-egg six times larger than expected, equal in size to the eggs laid by their giant relatives, the moas. Colossal, up-to-500-pound, flightless birds, moas were hunted out of existence by the Maori, the early Polynesian settlers of New Zealand.
Female kiwis lay one, two, or rarely three of these gargantuan eggs in a breeding season, spacing them about 33 days apart. After each egg is laid in the underground burrow or under the protective cover of a log, male kiwis have the only slightly less onerous task of incubating the egg for 70 to 85 days, nearly twice the duration of most bird species. If a subsequent egg is laid, the male incubates even longer. Along with the wandering albatross, the brown kiwi holds the record for the longest incubation period among birds.Although it was once believed that the marathon incubation was necessary because the kiwis eggs were too large for the birds to heat adequately, it now seems more likely that the kiwis unusually low body temperatures of 98.6 to 101.5 Fcloser to those of mammals than to the typical bird temperatures of 100.4 to 110.8 Fare responsible for the slow development.
In addition to their remarkable size, kiwi eggs have the distinction of being the most nutritious among bird ova. Whereas most precocial bird speciesthose in which chicks hatch downy, active, and wide-eyedlay eggs containing 35 percent yolk, kiwis manufacture energy-rich eggs containing 61 percent yolk. The proportion of yolk to the total mass of the egg is directly related to the degree of development that occurs before hatching. The payoff for all of this yolk investment is a fully feathered, mobile hatchling that requires virtually no maintenance for the first 72 to 84 hours alfresco. The baby lives off of a belly full of yolk it consumed before hatching and prepares for its first father-chaperoned foraging expedition outside of the burrow.
The obvious question, of course, is how did such a little bird evolve such an enormous egg? The traditional (and perhaps incorrect) answer is that large egg size is an advantage because well-developed chicks can fend for themselves with minimal parental care. However, it appears that the kiwis egg did not balloon over time, but rather that the kiwis ancestors were much larger birds, similar in size to the 500-pound moas. As the proto-kiwis evolved to their present size, their eggs did not follow suit and became increasingly disproportionate.
Among the ratitesthe group of flightless ground birds that also includes African ostriches, South American rheas, and Australian/New Guinean emus and cassowarieskiwis are the evolutionary mavericks. The common ancestor of ratites lost the ability to fly about 80 million years ago. As these land birds developed massive leg muscles, they dispersed throughout Gondwanaland, the supercontinent that broke up into the southern continents of today. The ratites gradually lost the cartilaginous keel that is prominent along the breast bones of flying birds, a feature that normally provides an anchor for one end of the powerful flight muscles.
Hatching a Plan
New Zealands indigenous Maori revered the kiwi as the eldest child of Tane Mahuta, the god of the forest. Kiwi feathers were woven into ceremonial cloaks called kahukiwi that were draped over the shoulders to signify royalty. Maori feather hunters undoubtedly made a dent in the 12 million kiwis that inhabited New Zealands North and South Islands. But the kiwis real problems didnt begin in earnest until the early 19th century, when Europeans began clearing massive tracts of forest and introducing, intentionally and accidentally, 22 species of predatory mammals where once there were none.
Adult kiwis are feisty enough to hold off most predators, but when an incubating father leaves its nest unattended to forage, domestic ferrets (Mustela putorois furo) and the now ubiquitous stoats (M. erminea)also known as European common weasels or erminesnatch up 50 percent of the eggs laid each year and 95 percent of the chicks that hatch. These ferocious mustelids were introduced to New Zealand in a misguided attempt to control an exploding population of European rabbits, which were themselves introduced from exotic populations living in Australias New South Wales in 1838.
Seemingly well-behaved domestic pets are just as dangerous to kiwis. Researchers were horrified to discover that a single dog that was somehow introduced to the Waitangi Forest killed more than 500 adult kiwi within a six-week period. The North Island common or brown kiwi is now declining at an average rate of 5.8 percent each year, which translates into a population thats halving in size every decade.
In response to these sobering statistics, the Department of Conservation (DoC), the Bank of New Zealand, and the Royal Forest and Bird Protection Society launched the Kiwi Recovery Programme (KRP) in 1991. The preliminary steps of KRP involved answering fundamental questions about the distribution of kiwi species, their genetic variation, and the predatory behavior of stoats and other introduced mammals. The program got immediate results. During the first five years of research and management, DoC biologists were surprised to discover that two populations of birds previously described as brown kiwis (A. mantelli) are in fact a distinct species. These birds have been named tokoeka (A. australis), a Ngai Tahu word that means "weka with a walking stick." The weka is another bird endemic to New Zealand, and the walking stick probably refers to a kiwis habit of methodically bobbing its beak along the ground.
In the 1960s and 1970s, some conservationists took on the heroic task of catching adult kiwis by hand and releasing them in protected forests far away from loose pets. According to Rogan Colbourne of the DoC, kiwi catching is risky business. "Kiwis are fast runners," Colbourne explains, "particularly having the advantage at night on steep terrain and in thick undergrowth. Removing them from their burrows is an adventure in itself. The trick is dodging their striking feet."
Not all kiwis are equally cantankerous. "The North Island brown kiwi arent so bad," Colbourne confesses, "but the great spotted kiwi and South Island tokoeka can deliver nasty cuts." One cranky bird in Fiordland repeatedly attacked Colbourne, clasping his clothing with its beak and raking its claws along his leg.
Is conserving this species worth all of the personal abuse? "No question about it," Colbourne says. "In their own quiet way, kiwis have a lot of individual personality. And more important, New Zealand might have its share of endemic wildlife, but kiwis are our only order of birds unique to these islands. Very few countries could claim that, including the U.S."
With the stoats destroying so many eggs and chicks, the DoC initiated Operation Nest Egg, an experiment to see if the vulnerable stages of kiwi life could be bypassed by collecting eggs from burrows, raising the chicks on predator-free islands and at the Auckland Zoo, and reintroducing them to the wild when the birds were large enough to defend themselves. To replicate the incubating conditions that male kiwis provide in the burrow, Operation Nest Egg researchers fooled some wild birds into sharing their parenting secrets.
Dummy eggs with internal temperature sensors were placed under wild incubating brown kiwis. The results show that the position of the electronic eggs was rotated about 180 degrees per day. By applying these findings to eggs in incubators, the success rate for these hatchlings has steadily improved. In the last two years, the Auckland Zoo has hatched 21 out of 24 fertile eggs from North Island brown kiwis.
Rogan Colbourne, coordinator of the Operation Nest Egg (ONE) program, reports other encouraging statistics. "Little spotted kiwis are on the increase on offshore, predator-free islands [to which they have been introduced] and the Okarito brown population has increased by about 15 percent over the last five years. On the whole, the ONE chicks have an 85 percent chance of survival, and in October 1998, a mature ONE kiwi paired up with a wild North Island brown for the first time."
Recognizing that stoats are public-enemy number one for New Zealands birdlife, this year Conservation Minister Nick Smith allocated new funds to accelerate DoCs pest-management research. Colbourne admits that even though he and his staff have witnessed positive results in some areas, theres no hope for kiwis until the stoat threat is eliminated. Researchers will be experimenting with immuno-contraception, new poison baits, and various other biological controls to determine the most cost-effective and ecologically sound alternative. While the DoC currently uses hen eggs to lure stoats into mechanical traps, a recent study suggests that stoats are more strongly attracted to the odor of freshly killed rats, and that baiting traps with a synthetic, slow-release rat-smell may provide a more long-lasting lure.
In the end, all of these strategies will fail unless New Zealands human Kiwis take further action to save their endangered birds. Along with research and management, the Kiwi Recovery Programmes third avenue of action is to educate hunters, dog owners, possum trappers, and farmers about the potential threats their activities pose to the kiwi. DoC volunteers have initiated a door-knocking program in which volunteers inform residents about the plight of kiwis, sometimes surprising home owners with the news that kiwis are living virtually in their backyards.
Tui De Roy, a wildlife photographer, nature writer, and Kiwi herself, joined DoC officer Chris Rickard on his trip to refit Boris and other kiwis with new radio transmitters. She is guardedly optimistic about the fate of the kiwis. "New Zealands DoC boasts some of the most dedicated conservationists anywhere in the world," she says. "Under public scrutiny and skeptical politicians, they work with minimum salaries in all weathers trying to deal with a ubiquitous problem (mustelid predators). Our childrens children may be lucky enough to hear kiwis calling in our future forests, but only if we give the conservationists the funding they desperately need."
De Roy learned recently that the great spotted kiwis in the mountains behind her home have gone from an estimated 15,000 to barely 11,000 individuals in the last five years. Despite her obvious fondness for kiwis, she is straightforward about the birds prognosis. Without drastic action, New Zealands honorary mammals may soon follow in the footsteps of their closest kin, the extinct moas.
A 1999 graduate of Williams College, author Tim Stoddard was an intern in the FONZ Communications Office. He is now working toward a masters degree at Boston University.
ZooGoer 28(6) 1999. Copyright 1999 Friends of the National Zoo. All rights reserved.
