Science / Medicine : Predators Endanger New Zealand’s Unique Species

18 million years, New Zealand’s birds, reptiles and invertebrates have existed in a peaceful paradise of splendid isolation.

Because New Zealand’s islands broke away from the ancient southern continent, Gondwanaland, before the evolution of mammals, no carnivorous mammals (or crocodiles or poisonous snakes) hid in wait for New Zealand’s native wildlife. So evolution has crafted a unique community of flightless birds, huge, conspicuous invertebrates and primitive plants, frogs and snails that are uniquely vulnerable and found nowhere else on Earth.

With little need of flight to escape from enemies, birds’ wings grew rounded and weak. Eventually, many birds became entirely flightless: the kiwi, the plump blue notornis, the weka, a flightless rail, are just a few. Early European explorers described with alarm how one unique flightless bird, the kakapo--a nocturnal parrot, the heaviest parrot on Earth--would drop like a rock from a branch when it was alarmed, not even bothering to spread its stumpy wings. (The kakapos climb up trees with powerful feet, but getting down is more difficult.)

Invertebrate animals, with few predators to hide from, evolved into spectacularly large, bizarre forms. The giant weta, the heaviest insect on earth, looks like a maple-colored cricket the size of a human fist. It weighs more than a mouse. Without the pressure to reproduce quickly before they were eaten, many species evolved leisurely lives. The Powelliphanta land snails, for instance, live 40 years or more and do not lay eggs until around age 15. The average American garden snail is lucky to live to age 2.

And New Zealand’s extraordinary safety from predators and browsing mammals allowed many of Gondwanaland’s original plant and reptile inhabitants to survive here and here alone. New Zealand alone hosts the tuatara, the last remaining species of the Rhynchocephalons, an ancient order of reptiles that lived among the dinosaurs. Only in New Zealand does the world’s most primitive fern survive (Loxoma), the world’s most primitive frog (Leiopelma) and the multilegged peripatus, which looks like a millipede but is more ancient.

These traits render New Zealand’s primitive, peaceful wildlife at once uniquely valuable and vulnerable. They were largely defenseless in the face of man’s introduction of mammals such as weasels, dogs and cats, and these introduced animals are devastating the wildlife here. Because so many of its birds are poor fliers, ground nesters or entirely flightless, 70% of the nation’s unique bird species are threatened with extinction, largely at the jaws of introduced predators. Nearly 200 kinds of invertebrate species are endangered.

Ninety-five percent of New Zealand’s vanishing native species are found nowhere else in the world. “There is enormous scientific value to these remnants of things that have vanished everywhere else in the world,” said Richard Sadlier, an ecologist with New Zealand’s government-funded Department of Scientific and Industrial Research. “And once they’re gone from here, they’re gone forever.”