Book of the Month: The Unburnt Egg
Museum natural history collections have been called libraries of life. Their very purpose is to help us probe, understand and enjoy the world’s astonishing biodiversity. In The Unburnt Egg Brian Gill continues his spellbinding stories from more than thirty years as a curator.
Some tales are bizarre they read like fiction: a population of ship rats decimating the entire wildlife of an island and then collapsing; birds leaving their young to be raised by other birds; frogs and lizards living in trees and flying.
Others reveal the painstaking detective work involved in solving mysteries presented by police, biosecurity agencies, government departments and members of the public. Frogs’ legs on sale as chicken, a feather hidden in a bag of sugar, a live boa constrictor on a street in snake-free New Zealand—it’s all in a day’s work. Into these stories Gill weaves as fascinating a cast of characters as you are ever likely to meet.
Brian Gill is former curator of birds and other land vertebrates at Auckland Museum, author and co-author of many books, including The Owl that Fell from the Sky (Awa Press, 2012), New Zealand’s Unique Birds, The Kiwi and Other Flightless Birds, and New Zealand Frogs and Reptiles, and a contributor to New Zealand Geographic and Forest and Bird.
Extract
A plague of rats – and its lesson for human survival
In 1955 a scientific party trapped a ship rat on Big South Cape Island, located 1.5km from the southwest coast of Stewart Island. This must have been an isolated individual because the mutton-birders – who came to this island for their annual collecting season from February until the end of autumn – for several years afterwards saw no damage to the soap, candles, bags of flour and other items they were accustomed to leaving exposed in their huts.
More rats must have reached the island. In autumn of 1963 a mutton-birder noticed some potatoes in his hut had been chewed. Next season damage was more widespread, and in March 1964 news of the rat problem reached the Wildlife Service in Wellington.
The officers who arrived to investigate in April found the birdlife and large insects in the north of the island greatly depleted. The service placed bait stations containing rat poison near some of the huts on Big South Cape and all over nearby Solomon Island, which was north of Big South Cape. The poison may have delayed the spread of the rats but soon they were everywhere. Robins and fernbirds quickly died out and other bird numbers declined.
In August and September the Wildlife officers transferred some birds of the rarest species from Big South Cape to nearby rat-free islands. Six bush wrens were caught for transfer to tiny Kaimohu Island but it was difficult to keep them in captivity and three died. In a final push, three more were caught and a rendezvous was arranged for the next morning with a Royal New Zealand Navy fisheries protection launch.
The seas were too rough for a dinghy to land on Kaimohu. Instead, the launch attempted to nose up in the swell towards a rocky shelf. Brian Bell, leader of the Wildlife Service party, bravely jumped ashore. Boxes containing the wrens were landed by running them from the boat along a taut line and Bell set the wrens free in the nearby scrub. To get back he attached the line to his life jacket, jumped in the cold swell and fought to stay afloat until he was hauled aboard.
Bird translocations were a new idea then, and the work was pioneering and experimental. Wildlife officers were back on Big South Cape in February 1965 but could find no wrens for transfer. Two were seen on Kaimohu in 1972 but an inspection in 1977 and subsequent visits revealed none. It is clear now that these had been the last of the bush wrens and their absence had signalled the extinction of the species.
The rat plague on Big South Cape Island did even more damage: it eliminated a population of snipes now regarded as the last survivors of the South Island snipe, Coenocorypha iredalei. Two snipes were caught on Big South Cape in August 1964 but died as bad weather was preventing their transfer to a rat-free island. Also exterminated by the rat invasion was the greater short-tailed bat, Mystacina robusta.
However, there was a good-news story. In 1964 thirty-six South Island saddlebacks, Philesturnus carunculatus, were caught on Big South Cape and transferred to Kaimohu and Big Islands. More were rescued in 1965. Numbers on the new islands increased and in the last fifty years this species has been translocated to, and established on, many southern islands. The North Island saddleback, Philesturnus rufusater, was saved in a similar way. The saving of these birds was a world first—the first time a bird in danger of extinction was restored to viability by direct intervention.
How had ship rats reached Big South Cape Island in the first place? The answer was that they had probably arrived on fishing boats used to transfer mutton-birders to the island and had run along the mooring lines, then swum to shore. As the island had been rodent-free, the rats had no competitors. There were also few other predators, just flightless weka and moreporks.
Very soon the whole of Big South Cape Island was swarming with rats. All horizontal surfaces in the huts of the mutton-birders were fouled with rat droppings, and rats were nesting among their bedding and inside their mattresses. Many kinds of birds were fast declining as they and their breeding attempts succumbed to rat predation. The largest and most accessible kinds of insects were also hard to find. Fallen berries had all been eaten, certain kinds of highly palatable plants were defoliated, and any edible seedlings on the forest floor were chewed to ground level. The island was becoming a hellhole.
Nature’s feedback mechanisms now increased in proportion to the problem. As hunger prevailed, the condition of the rats would have deteriorated. They lived shorter lives, and reproduced less prolifically. The fewer litters of fewer offspring contained many sickly young. At peak density the rats would have been in constant contact, with high levels of aggression and fighting. Stress hormones were at unhealthy levels and there must have been cannibalism. High rat numbers would have allowed any infectious diseases and transmissible parasites to quickly run rampant through the whole population. In the huts, the desperate rats stripped wallpaper off the walls to eat the flour paste. Rat numbers then crashed cataclysmically.
But some rats survived. As the vegetation recovered and those prey animals that had not been eliminated multiplied again, rat numbers would have increased. This time the rat population remained in equilibrium with the island’s degraded resources. Finally, a special poisoning campaign— using the techniques attempted on the island in 1966 but now improved—saw rats eliminated in 2006.
The events on Big South Cape Island show in microcosm what happened several times across the whole of New Zealand as native birds faced the arrival and spread of new predatory mammals. But the story is even more instructive: the events reflect what is happening over the whole planet. People are the ship rats. Big South Cape Island is the Earth, a piece of territory of finite size, able to support only so many people, with a limit on human numbers and economic growth. We have occupied all the world’s habitable regions. Our population has reached about 7.4 billion. Our numbers are now in the dreaded phase of exponential growth, rocketing uncontrolled and uncontrollably to an uncertain future. Every second an average of 1.8 people die—but another 4.3 babies are born. Some predictions are that the human population will soon level out but not before rising by more than fifty percent. Whatever happens, there are clearly too many of us and our activities are causing too much damage to the environment on which we depend. Some put their faith in technology to solve all the problems. Realists doubt that human ingenuity can cope when it would have to produce the required innovations at an accelerating rate—indefinitely.
Countries want the impossible—economic growth without end—and our main politico-economic structures promote few alternatives. Yet endless economic, material and population growth is as damaging and pointless as was the proliferation of rats on Big South Cape Island.