Rat Island

by William Stolzenburg

  Williams began by calling to the stand the botanist and foot soldier Ian Atkinson, who in his surveys of offshore islands had found all three of New Zealand’s invading rats repeatedly implicated in serious depredations. The first item in Atkinson’s deposition was the brown rat, largest of the three and weighing up to a pound. Legendary sewer rat of the cities, the brown rat was primarily a burrowing ground-dweller, invader of New Zealand’s streamside forests and—most ominously for those natives clinging to New Zealand’s near-shore archipelago—a willing and accomplished swimmer.

  Next up was the ship rat, more an agile climbing rodent, sometimes called the roof rat, sometimes found in walls and attics, but at home as well in the wild forest canopy—and especially lethal to tree-dwelling birds.

  Smallest of the three was the kiore, or Pacific rat, the globe-trotting guest and stowaway of the Polynesian voyagers. Not so eager a swimmer as the brown rat, not so capable a climber as the ship rat, and ultimately a loser in competition with the other two, the kiore had been all but eliminated from the mainland of New Zealand, relegated to several dozen outlying islands.

  Atkinson argued that all three acted directly as predators of New Zealand’s native animals, most conspicuously of its birds. He had gathered a list of formal reports and observations of the carnage. The list ran long and wide. The brown rat was implicated in the eating of penguin eggs on the subantarctic island of Campbell, mallard eggs in New Zealand, puffin eggs in Britain, rail eggs in California, and tern eggs in Cape Cod. The big rat’s diet also included petrel chicks in Marlborough Sounds, shearwater chicks and parents in British Columbia, and petrels of all ages in the Hauraki Gulf.

  The ship rat was known for, or highly suspected of, taking tern eggs on the remote Pacific island of Palmyra, tropic bird eggs on Bermuda, and petrel chicks from Hawaii to the Galápagos. It had eaten the thrushes, warblers, white-eyes, fantails, and starlings unique to Lord Howe Island, in the Tasman Sea, birds that were never seen again.

  Even the supposedly benign little Pacific rat, the Māori’s revered kiore, under closer scrutiny grew to a giant-killer. It ate the eggs of New Zealand’s robins and tuis; it ate the chicks of its petrels and terns. And the most astounding demonstration of the kiore’s predatory powers would scarcely have been believed had it not been witnessed.

  In the mid-1960s, while studying Laysan albatross on Hawaii’s Kure Atoll, an American ornithologist named Cam Kepler had come upon incubating birds dead and dying on the nest. Over two seasons Kepler and crew found fifty such birds. The albatross—five-pound giants with seven-foot wingspans—had suffered gaping wounds on their backs. The sores spread up to seven inches across, holes deep enough for Kepler to peer inside to the birds’ ribs and lungs. It wasn’t until he visited the colony at night that the cause of the mysterious mutilations came to light. Kepler walked up on a wounded albatross sitting in the open. “I shut out my light and sat down to watch, waiting a few moments before shining the headlight again on the albatross,” he wrote in a note to the journal Auk. “When I did so, many rats scampered off his back where they had been feeding.”

  The rats were eating and killing albatross, in that order. Kepler watched the rats—more than twenty of them—swarming upon the bird and feeding from the expanding wound. The besieged bird would turn and toss rats with its bill; others would scramble to take their place. By the next morning, the rats were cleaning the bones of a dead albatross.

  So much for the harmless kiore. That all three rats of New Zealand were both capable of and practiced at killing birds small and large, Atkinson’s review would seem to have left little doubt. He concluded with a fatalistic caution, warning of the inextinguishable threat and irreversible changes to the native fauna, once rats established their beachhead.

  From the audience a hand went up. It belonged to Kazimierz Wodzicki, an esteemed professor from the University of Wellington. Wodzicki had some twenty-five years earlier written the book on New Zealand’s invasion by mammals, on their decimation of crops and forests and fisheries. But Wodzicki was now oddly assuming the skeptic’s role. From Atkinson’s global list of rat carnage—a list that would run four pages long—Wodzicki singled out one case that seemed to exonerate the rat as independent agent of destruction. He pointed to Atkinson’s example of Kure Atoll’s’s colony of tropic birds, an elegant, long-tailed seabird whose numbers had apparently waxed and waned more with the weather than with the rats.

  “The essential point is that the population did not really diminish,” said Wodzicki. “There were years when the population went down but with favourable weather conditions subsequently the tropic birds were not molested. Generally, over a period of 10 years, the kiore had an impact just like that of wolves and hares in Europe.”

  With his wolves and hares, Wodzicki had invoked a textbook case of the nascent field of ecology, of predator and prey populations oscillating gracefully through cycles of feast and famine, the two undulating in choreographed counterbalance to neither’s ultimate harm. According to Wodzicki’s continental analogy, the rat-borne fears were overblown.

  But there was something disturbingly askew in the professor’s logic. These were not wolves and hares, perfecting their dance of death over the eons, but rats and birds thrown together as strangers in a last-minute hiccup of history. These were contests being waged not in the sweeping geographies of the continents but in the confined arenas of little islands. Wodzicki’s theoretical swipe at the worriers had revealed a fundamental divide of ecological worldviews, dividing those who saw such invasions as a scientific curiosity deserving further study from those who saw them as a wildfire to be fought for dear life.

  That little divide would rapidly widen. Next up was Brian Bell, there to retell the story of Big South Cape. If Atkinson had left any doubts about the end point of rats loosed upon islands of innocent birds, Bell was determined to let the evidence of Big South Cape forever vanquish them.

  Bell briefly reviewed the pre-rat history of the Big South Cape tragedy, describing the seasonal tradition of the muttonbirders and their innocuous little settlement of cabins, the relative lack of human inroads by means of fire and clearing—in essence, the enduring balance of relative purity of an island standing whole amid a contrasting century of mainland New Zealand’s biotic impoverishment.

  “It was the birdlife,” Bell said, “its variety and abundance, which first took the visitor’s attention.” When he and Don Merton had first stepped ashore, the forest of Big South Cape had clamored so conspicuously with the song of New Zealand’s emblematic natives—its parakeets, bellbirds, fernbirds, and robins. Here also one could still find the rarest of the remainders, the South Island saddleback, the Stead’s bush wren, the Stewart Island snipe, and the greater short-tailed bat, the last survivors from the bygone era of New Zealand’s innocence.

  Then came the crash of 1964—the reports from the muttonbirders, arriving to find their camps ransacked by rats; Bell and Merton’s belated reconnaissance to find the forests in tatters and the birds obliterated; and the tragically delayed rescue, wherein Bell and Merton watched as two species of bird and the incredible crawling bat were lost forever.

  Muttonbirders and bird-watchers would eventually come together, with poison to knock the rats back. But by then the damage had been done. Said Bell, “Since the irruption has passed and the rat population has reached a more stable level, bird populations have settled to a level one would expect in mainland situations where rats have been present for a long time.” Big South Cape was no longer a wild relict of primeval New Zealand, but a mere miniature of the eviscerated mainland.

  In closing, Bell could not resist a parting shot at those who had fiddled while Big South Cape had burned. He had not forgotten those five agonizing months that he and Merton had been kept waiting for permission to mount a rescue. “The Big South Cape irruption is now history, but what has been learnt from it?” he asked. “Unfortunately less than one would like because, despite the request made by the Wildlife Se
rvice, no research worker could be found at the time to study the rat irruption and its effects.” And little was being done to prevent the repeating of that history. Fishing boats were still anchoring close to rare sanctuaries; rats were still jumping ships and crawling down anchor chains. There were more Big South Capes waiting to happen.

  And for some, that was apparently OK. In the Q&A that followed the day’s briefings, Bell’s rendering of the Big South Cape tragedy came under fire. “In my view there were actually two forces acting from the beginning,” said Wodzicki, taking the first jab. “The habitat of all these islands had been seriously deteriorating through both fires and the construction of buildings and tracks. My impression is that the birds were previously in an endangered state in which only one more stress was sufficient to tip the scales.”

  “I think you may have misunderstood me,” the junior Bell jabbed back. “I was trying to emphasize that there had not been very much modification. The birding on South Cape is very limited in area and the modification caused by the erection of homes is very minor.”

  Wodzicki: “My point is that, although the rats were a very important new factor in the Cape, in a healthy population at least some of the other species would become adjusted to them.”

  “Some of the species obviously did,” answered Bell. “But unfortunately some did not.”

  Unfazed by the gravity of Bell’s counter, Sir Robert Falla, considered perhaps New Zealand’s senior ornithological authority, joined the attack. Falla had not been consulted before the Big South Cape rescue parties had finally gone in. He had objected to the use of poison afterward. Insiders knew Falla as no fan of the Wildlife Service, for which Bell now worked.

  “The hypothesis I am putting forward is that this could have been a classic irruption of a population already present for a long period but at a low level on at least one of the South Cape Islands,” said Falla. “There is a difference between this theory and the theory of a fresh invasion of healthy rats running ashore along the mooring ropes of muttonbirders’ boats. On the acceptance of that second theory of the rat situation the management reaction is to say, ‘My God, we have got to do something’. If you accept the former hypothesis you are justified in saying we do not need to do anything.”

  Bell could only shake his head at the lunacy of the logic. He and Merton had already seen firsthand what the “we do not need to do anything” hypothesis had done for rescuing Big South Cape, and it could be summed up by three irreplaceable living species eternally rendered to museum cabinets.

  The conference reports to follow offered little in support of a truce with the rat. More details mounted on the woefully inadequate defenses of seabirds in a new world of rats, of mass killings and lifeless bodies with craniums excavated, of entire colonies cleaned to the very last chick. There followed news on the disappearance of New Zealand’s giant weta—an insect larger than a sparrow—which had been swept wholesale from northern forests in the wake of the brown rat. Another New Zealand specialty, the reptilian oddity known as the tuatara, reported the herpetologist Tony Whitaker, had been all but wiped from the mainland and chased by the kiore to the country’s last uninvaded islands.

  “One thing that disturbs me,” interjected Wodzicki, searching again for other culprits, “… why did [the rats] wait until our time to attack the tuataras …? If kiore were present since the [Europeans] arrived, how could the tuataras have survived?”

  Whitaker’s retort painted a frightening scenario. “The tuatara is a very long-lived animal,” he said. “Estimates of its life-span range up to two hundred years. I do not think you could suggest that the introduction of rats would stop breeding of tuatara overnight.” Whitaker was implying that the last of the world’s tuatara amounted to ancient, aging relicts, individually immune to attack owing to their overwhelming size, yet collectively doomed to extinction by rats that were devouring every last one of their young. Said Whitaker, “The fact that we are finding no animals less than two hundred millimeters in length could well explain this.”

  The second day of the conference moved to the question of what, if anything, could be done about the rats. Hopes were scarce. There was talk of spreading chemicals that would render the rats sterile—an approach entailing months of vigilance and tiny odds of success. There was a proposal to fight the island rats with stoats—those same little foreign weasels that had helped drive New Zealand’s native avifauna to the islands in the first place.

  The war on rats offered at best an eternal struggle, at worst a lost cause. In his closing of the conference, chairman John Yaldwyn summed up the general mood with what would become an infamous statement of surrender. “Nothing that has been said this afternoon, even the use of stoats for control, would make me think differently,” he said. “We have control methods, and methods for reducing populations, but complete extermination on islands is remote or at least a very very difficult thing indeed.”

  RAT FIGHT

  For most in the audience Yaldwyn’s waving of the white flag seemed a sensible concession. But for at least one, it bordered on insult. The junior wildlife technician Bruce Thomas had sat through the meetings as more of a wide-eyed spectator, listening as the big guns boomed. But now, to hear it all end with this pessimistic talk of remote possibilities struck an indignant nerve. Hadn’t they all just heard, as he had, about Maria Island?

  Earlier in the meeting the noted ornithologist Sir Charles Fleming had raised the question of Maria. He had been intrigued by news of rats having somehow been extinguished from the little island years before. Said Fleming, “This is the first example I have heard of the extermination of a rat population by any control measure.”

  It was Don Merton who sixteen years earlier, after investigating the slaughter of some nine hundred petrels on Maria Island, had helped the bird-watcher Alistair McDonald spread rat poison there. Surveyors would later return to discover that the island’s rats had been more than knocked back. A handful of hardy volunteers, with a seat-of-the-pants strategy and a pauper’s budget, had wiped every last rat off Maria.

  It was only one three-acre island in an archipelago of hundreds far larger, yet the finality of the outcome had gotten the upstart Thomas thinking heretical thoughts about the otherwise invincible rat. Thomas had by then familiarized himself with the enemy more intimately than most. Raised on a dairy farm in the New Zealand countryside, he had grown up in the company of rats—rats that came scrambling for the leavings at the pigsty, rats that swarmed upon the stream banks where young Thomas wandered. Thomas was at turns fascinated by these wild invaders and keen on seeing them dead. He would sit quietly and watch the rats going to and from their holes, darting here and there to steal a mouthful. He would bait the doorways of their burrows with milk curds, shoulder his slug gun, and, with his fox terrier at his side, wait for the rats’ inevitable kamikaze dash. Sometimes the dog almost beat the bullet to the target. But invariably there was always one more rat where the last one had come from.

  After high school Thomas came under the wing of a biologist named Rowley Taylor. Taylor, as it turned out, had an unusual respect for rats too. His interests had gravitated early toward an animal that others in the profession had passed up for more charismatic subjects. Island to island, across the New Zealand archipelago, Taylor had watched and trapped, skinned and identified rats. It amazed him how few biologists could, or even bothered to, distinguish one species from another. By the time he was thirty, nobody knew New Zealand’s rats better than Rowley Taylor. He admired the rats’ talents—their toughness and intelligence, their wariness and agility and explosive fecundity, their willingness and capacity to eat anything that couldn’t eat them first. But at the time of the Wellington rat conference, knowing what he knew of those talents, Taylor could not argue against Yaldwyn’s bleak prognosis for defeating New Zealand’s most indomitable pest.

  Taylor’s protégé Thomas, on the other hand, was yet too young to be intimidated by such odds. While his elders were nodding their heads in
unison, conceding defeat, he had already begun imagining a preposterously more hopeful scenario. Thomas had ideas for ridding an island of rats that would dwarf by leaps of magnitude the serendipitous little campaign at Maria Island.

  Two years before the Wellington meeting Thomas had accompanied a biological expedition off the coast of Fiordland. Breaksea Island was 440 acres of steep and forested rock separated by more than a mile of rough water from the nearest harbor. In all its wildness and isolation the island was being considered as a potential sanctuary for the ailing kakapo, before the surveyors reported back. Thomas and his companions were to find the would-be fortress of Breaksea overrun by brown rats. The rats would summarily scuttle any plans for bringing kakapo to the island. But Thomas, watching the impertinent hordes scurrying through the scrub like rush hour pedestrians, began entertaining a more heretical idea. Why not just rid Breaksea of every last rat?

  Unknown to Thomas at the time, there was a discovery under way in an overseas lab that was about to elevate his fantasy to the realm of possibility. Agricultural chemists in the United Kingdom had come up with a new poison.

  THE SLEEP OF DEATH

  Since the 1940s there had been a global campaign against the rat as crop pest and urban scourge, and it had largely been fought with massive doses of a chemical named warfarin. Warfarin was a poison of rather benign origins. It was an anticoagulant, a thinner of blood. It had originally served as a human treatment for thrombosis, an overclotting of the blood, a precursor to stroke and heart attack. When lab workers had subjected lab rats to high doses, though, they had died. The minor and sundry repairs of little broken vessels that constituted the daily workings of healthy bloodstreams became, with an overdose of warfarin, the unstoppable leakage of lifeblood. Victims of too much warfarin died the death of a thousand cuts.

  It did not take great leaps of imagination to see the darker utility of this lifesaving drug. As a killer of rats, the anticoagulant approach offered immediate advantages over the leading chemical weapons of the day. Strychnine, arsenic, thallium sulphate, and zinc phosphide, among others—acute poisons targeting brain and nerve—produced fast and sometimes violent reactions in their victims. Whatever few rats somehow survived—and there would always be those few—learned a lesson never to be forgotten, or repeated. Those that watched the tortured writhing of their comrades learned as well. A rat with the look and smell of danger burned into its memory was thereafter an invincible rat. It would sidestep and dodge, hunker and wait, until the poison-bearing enemy grew weary and decamped. Then it would gather its colony mates, and in true rat fashion they would restock their pack with a wiser, warier, tougher force of rats. Warfarin, to the contrary, gave few such warnings.