The New Nature Page 15
All this makes good sense, but what about the appearance of shovellers and black-winged stilts? Shovellers are big-billed ducks that dabble in ponds, and stilts use swamps. How could the Maori have helped these? I found an answer in Peter Wardle’s book Vegetation of New Zealand: ‘The greatly increased incidence of fire after the arrival of Polynesians 1000 years ago transformed wooded swamps into herbaceous swamps, and increased sedimentation through deforestation of catchments, thereby creating new wetlands’. New wetlands! All the new birds used swamps. A Maori farmer torches a forest on a hill and far below a home is created for an Australian duck. Nature in New Zealand, then, is not as natural as we might think. Fifteen of the ‘native’ birds (a fifth of all species on the two main islands, excluding seabirds) are there because people killed trees. This situation is only known to a few fossil workers. The status of pukekos and harriers as New Zealand birds goes unquestioned by birdwatchers.
Some of the newcomers are doing real harm. The endangered black stilt has been reduced to a few hundred survivors along riverbeds on the South Island. While its numbers have dropped (blame stoats and lost habitat), those of the black-winged stilt have jumped, thanks largely to farmers converting swamp forest into sodden farms. The blacks, now short of mates, are accepting advances from the Australian invaders. I have seen their hybrid young in paddocks, and a sorry sight they are – not quite this and not quite that. The world’s largest stilt is doomed.
As well, harriers sometimes kill rare birds (kokako and brown teal), and silvereyes spread more weeds than any other ‘native’ bird; most of the lantana near Whangarei is silvereye-spread. Masked lapwings are implicated in several problems. ‘One is that they cause bird strikes at airports,’ says Paula Warren, principal policy analyst with the Department of Conservation. ‘And they’re beginning to show some signs of doing crop damage. They’ll also have an impact on the rare birds that occupy the braided river habitat.’ She concedes that the status of new birds needs rethinking. ‘We haven’t really grappled with the question yet.’ She wants new birds culled if they misbehave.
New Zealand will keep absorbing our birds. Drop-ins over the years have included brolgas, pelicans, wattlebirds, and the monarch found in a cat’s jaws in 1996. Some, including masked woodswallows from the Outback, have even bred there once or twice. Ibises, wood ducks and kestrels could do well in future; so too the hardhead, a duck that lived there during the nineteenth century until it was wiped out by a volcano. In the north of New Zealand global warming will favour Australian insects. Expect to see more Australian butterflies in Auckland gardens, and more spiders.
Australia has been exporting birds in other directions too. Six species have gone to Norfolk Island and Lord Howe Island off to our east (silvereyes, swallows, white-faced herons, swamphens, kestrels and black ducks). Christmas Island, way off to our west, has gained white-faced herons and nankeen kestrels, and masked lapwings reached New Caledonia so recently that by 1999 there were only eleven. Australia has even influenced the remote Chatham Islands, east of New Zealand, where silvereyes and swamphens now roam. On each of these islands the story is the same: when trees fall, Australian birds invade, sometimes causing strife. An airforce Hercules was grounded on Lord Howe when a lapwing was sucked into an engine. Swamphens there raid vegetable gardens. On Ned’s Beach, where fish are fed bread, black ducks startle tourists when twenty or thirty waddle up for a handout; the Lord Howe population of 40–100 is largely bread-fed. Surreptitious culling of all these birds goes on. Conservation concerns include kestrels attacking endangered bats (on Christmas Island) and rare white terns and petrels (Norfolk Island). Silvereyes may be displacing the critically endangered white-chested white-eye on Norfolk. Only twenty or so remain.
These changes are part of a global phenomenon that includes movement into as well as out of Australia. In The Wind in the Willows Rat begs the swallows not to wing south for winter. ‘Couldn’t you stop on for just this year?’ he pleads. They heed him not. Rat would be saddened to know that barn swallows venture further south today than ever before. In Africa during the 1960s they expanded their range by hundreds of kilometres, and swallows from England now visit South Africa. Australia’s first recorded barn swallow was seen in 1860, the second in 1960. Now they flock to our tropics each summer in the hundreds, perching on powerlines over paddocks. Our swallows come from northern Asia. One day they may reach Sydney, a prospect that would have warmed bosoms in the acclimatisation societies of yore, so keen were they to fill Australia’s fields with birds they knew from England. Barn swallows probably come here for the same reason Australian swallows spread abroad. Grassy paddocks attract the flying insects they eat, and powerlines make good perches.
We have weakened the barriers that separate Australia from other lands. Birds are leaking in and out. New Zealand, in exchange for fifteen of our birds, has given us something to wonder about: the kelp gull. It’s a hefty, black-winged bird that multiplied in New Zealand after learning to loiter around whaling stations and ports. ‘Since the establishment of meat-preserving and boiling-down factories in certain spots,’ noted bird expert T.H. Potts in 1882, ‘these birds may be observed collected together in thousands, feeding on the refuse which has been carted away from these great butcheries.’ These gulls also attack sheep. Walter Oliver observed that ‘victims may be old sheep with a heavy fleece which may fall and be unable to rise, or weak lambs’. He said the kelp gull ‘eats the eyes, pecking back into the brain, and also eats the tongue’. New Zealand has another mutton-munching bird, the kea, a big parrot that perches on live sheep and scoops out their flesh. The two birds are outstanding examples of animals exploiting abundant resources.
It was inevitable that kelp gulls would wander over here – there’s plenty of refuse. I’ve counted a couple of hundred of them at the Hobart tip. They were gobbling down newly dumped wastes, but weren’t clever enough to peck open plastic bags. A study in Tasmania found that rubbish – plastic, glass, string, paper, aluminium foil, chop bones – made up 55 per cent of the pellets these gulls spew up after feeding. Refuse on both sides of the Tasman has fuelled their invasion. Kelp gulls are yet another long-range consequence of human waste disposal. They may pose a threat to our own Pacific gull, a related bird. Around Hobart Ruth and Graeme Coulson found that Pacific gulls at first drove kelp gulls off beaches, but over time, as kelp gulls multiplied on their refuse-tip diet, they muscled their way onto the coveted sand.
Cattle egrets are handsome white birds that now feed around cows, grabbing grasshoppers flushed by their feet. A hundred years ago they were only found within Africa and South-East Asia; now they occupy Europe, the Americas, India, and many far-flung islands. Their ancestors probably fed around elephants and buffalo, but cow paddocks are now their main habitat. They entered Australia during the 1940s and now range right down to Tasmania, thousands crossing over to New Zealand each year but returning here to breed.
The yellow wagtail – a little tail-wagger – is another Asian arrival. When Graham Pizzey updated his 1980 bird guide in 1997 he upgraded this bird from ‘vagrant’ to ‘regular summer migrant’. Yellow wagtails like ovals, airfields, ploughed fields and lawns. I’ve seen them at the Broome sewage farm. Farms and parks in Indonesia probably lured them further south. Other birds that may well be invading as we speak include the house swift, grey wagtail, little-ringed plover, spotted whistling-duck, and New Zealand pied oystercatcher, which was first seen here in 1999. There are also the white-breasted waterhens breeding on Christmas Island and the pale-headed munias that recently arrived on Ashmore Reef. We may soon get the pied chat, a lawn-loving bird that invaded Port Moresby in 1960. Change, and more change.
For some of these birds, ricefields in Indonesia provided stepping stones to Australia. Agriculture in Asia dates back thousands of years, and it’s possible that early clearings carved into the rainforests of Java and Sumatra helped other birds colonise Australia in the distant past. Several birds native to Australia today – the black
kite, king quail, Richard’s pipit, singing bushlark and two cisticolas – are native to Asia as well, and they use farmland in both places. The most intriguing of these, zoogeographically, is the zitting cisticola. It’s a cute little bird found flitting about in grassland in northern Australia. Its distribution is vast, stretching all the way to Africa, its continent of origin. Dozens of cisticola species live in Africa, but only two, both very fond of farmland, have spread into Asia and Australia. Zitting cisticolas are also found in southern Europe, and during the 1970s they spread north into farmland in France and Germany. But there’s a puzzle here. If they can survive winters in Germany and Japan, why are they only found in the tropics in Australia? The answer, I am sure, is that zitting cisticolas are relatively new here. They arrived only a few hundred or thousand years ago and haven’t yet worked their way south. In Asia they live among crops, and I’ve heard them ‘zit-zit-zitting’ above Balinese rice fields. Our ‘native’ cisticolas are probably descended from Javan farm birds. Now that rice is grown along the Ord River in north-western Australia (and spreading there as a weed), cisticolas are thriving, their human-made Asian habitat having caught up with them. When I put this idea to Ron Johnstone, bird curator at the Perth museum, he said, ‘Sure, and grass owls too.’ He believes they also invaded Australia by utilising croplands as stepping stones.
Biologists have recently discovered a new kind of horseshoe bat (Rhinolophus) on Cape York Peninsula, in a region well picked over by earlier collectors. They suspect it moved in recently from New Guinea. The Torres Strait islands and far north Queensland are poorly endowed with caves, but old mine tunnels and wartime bunkers are now available as stepping stones. Artificial caverns may be helping foreign bats invade Australia.
Butterflies are also winging south. The pied flat (Tagiades japetus) was only known in far north Queensland and New Guinea in the nineteenth century, but by 1955 it had reached Cairns and it now flutters about on the banks of the Mary River in southern Queensland, having advanced 1800 kilometres in eighty-odd years. Its caterpillars eat yam leaves and may have benefited from yams grown in Torres Strait, allowing them to make the crossing from New Guinea to mainland Australia. I’ve seen great tangles of abandoned vines on some Torres Strait islands.
Another new Australian butterfly, the painted lady (Vanessa cardui), has performed a feat that defies belief. Well known in England and also found in Africa and Asia, it turned up many years ago around Perth. How did it get there? Experts suspect it crossed the Indian Ocean from Africa, a journey of about 9000 kilometres. The little black caterpillars like to munch on thistles and nettles, and weeds in Perth probably abetted the invasion. Australia’s other long-haul, four-winged immigrant, the North American monarch (Danaus plexippus), eats foreign weeds and nothing else, and we made its conquest possible by importing African and American cottonbushes. Sighted first in 1871 after island-hopping right across the Pacific, it’s now one of our best-known insects, called the ‘wanderer’ here. We brought the leaves and the butterflies came.
Distributions have changed all over the world. England’s sparrows, for example, should really be counted as invaders from Asia. From an ancestral home in western Asia, tree sparrows travelled all the way to Ireland, Japan and Bali. England once carried as many trees as New Zealand, and many of her farmland birds – barn swallows, starlings, skylarks, barn owls, and the like – probably invaded after the axe, as happened in New Zealand. But so feeble is England’s fossil record that we can’t say for sure. Skylark and starling bones at one Neolithic site in Orkney were found alongside charcoal, indicating forest fires lit by humans. Archaeologists can prove that such typically English animals as house mice, rats, rabbits and hares were introduced to Britain, and some of England’s birds are surely invaders too.
Biologists who study invasions often warn about globalisation of ecology (see my book Feral Future). Pests such as house mice and thistles have followed the trajectory of Coca Cola and blue jeans by going everywhere. More than a few of the animals mentioned here are also global winners. Cattle egrets, kelp gulls, pied stilts, swamphens, coots, cisticolas, barn swallows, sparrows, wanderers, painted ladies, common blues and long-tailed blues have all conquered three continents or more. The spread of exotic species evinces much alarm, but the shifts noted here hardly rate attention at all. That’s because they are accepted as natural events, when really they are influenced by our activities. Animals are responding to us in more ways than we want to admit.
1 The colonisers, listed in full, are Australian shelduck, Australasian grebe, white-faced heron, nankeen night heron, royal spoonbill, Eurasian coot, black-fronted dotterel, masked lapwing, welcome swallow, silvereye.
‘A good traveller has no fixed plan and is not intent on arriving.’
Lao Tzu
Blessed with flight, birds and butterflies can find their way to new places, but most other species need our help, relying on the services of trucks, trains and planes. In Australia today many an animal or plant is living somewhere new after hitching a ride. Sometimes they confuse our view of what is natural.
In 1987 spider expert Robert Raven came out with a surprising idea. He proposed that Australia’s famous outhouse icon – the red-back spider – was really an exotic invader. His idea was buried in a book and didn’t evoke much reaction until I wrote it up for Australian Geographic the following year. Robert, the Queensland Museum’s curator of spiders, then found himself at the centre of a media circus. He even inspired a cartoon in The Australian.
Robert had marshalled strong arguments for his case. Why, he asked, when redbacks are so abundant today, did biologists not name them until 1870? Two hundred Australian spiders were known to science by that time. How could something deadly, and so fond of houses, escape notice for so long? Robert also touched upon the spider’s commensal habits. Redbacks seem to prefer sheds, fences and piles of rubbish over natural bushland. In national parks they often do best around toilet blocks and picnic tables. ‘It is true that one may find these spiders established in the stumps, cavities in tree-trunks, or among piled boulders in the bushland,’ wrote Keith McKeown back in 1952, ‘but where man has settled and erected structures for his residence or his work, there the spiders seem most at home and their numbers reach the maximum.’ Like sparrows and kitchen cockroaches, redbacks behave like foreign invaders. The fact that they were first recorded by scientists at two ports – Rockhampton and Bowen – further suggests arrival from abroad.
I have gathered more evidence to back Robert’s claim. Very few Australians writing before 1880 mentioned redbacks. I can find no mention in any explorer’s journal, First Fleet diary or Aboriginal legend, and no obvious listing from an Aboriginal language. This is astonishing for something so dangerous that dwells in huts and stacks of firewood. Redbacks should feature in scores of tales and legends. From the 1880s onwards redbacks were attracting attention, but the comments from that era are puzzling. Look at what Frederick Aflalo says in A Sketch of The Natural History of Australia (1896): ‘Australia has some formidable tarantulas and other ground-spiders, and, more particularly in northern Queensland, there is a very venomous black and red kind which, like the “katipo” of New Zealand, feigns death when suddenly disturbed.’ Aflalo offered no name for this spider, which he confined to north Queensland. Professor Edward Morris used the Maori name ‘katipo’ in his 1898 dictionary of Australasian words. New Zealand katipos – closely related spiders – were evidently better known in Australia than redbacks. ‘Redback’ itself is a twentieth-century name.
Robert’s theory founders on the fact that no foreign home for the redback has ever been found. Redback colonies in New Zealand, Japan and Belgium obviously came from Down Under quite recently. In 1993 Barbara York Main drew attention to a diary entry written by adventurer Edward Snell back in 1850 which mentioned a ‘venomous black spider with a red spot on his tail’. Snell caught his spider near Adelaide. Robert Raven has now shifted ground. Redbacks originated in the more westerly po
rtions of Australia, he says, and came east by hitchhiking on trucks and trains. They are new to eastern Australia, but they came in from the Outback and not from overseas. It’s a theory that fits all the facts. Redbacks are sometimes found in natural settings in the western half of the continent. And there is this telling comment made by Keith McKeown in 1952: ‘For very many years this spider was looked upon as an inhabitant of the more dry and dusty inland districts, but within the last twenty years or so its numbers have increased considerably in the coastal areas, at least in New South Wales, and it is now just as firmly established there as elsewhere. This is especially true in the city and suburbs of Sydney, where I can remember the discovery of a Red-back being a rather unusual occurrence; now they are found in thousands.’ Outback birds have come east; why not a spider?
Redbacks do travel well. They are quick to colonise new homes when they arrive with lumber and guttering. To me they are an outstanding winner – an animal doing far better than ever before. They have reached New Zealand in crates of grapes (by impersonating juicy muscatels) and in old locomotives. They got to faraway Tristan da Cunha in the Atlantic Ocean after apparently travelling on an American satellite station that came from inland New South Wales via Honolulu and Miami.
People, by their mobility, create excellent opportunities for hitchhikers. Most unpaid passengers on our ships, planes, cars and trains are exotic pests, but Australian plants and animals also travel widely. Wherever there are highways there are native hitchhikers. Australia now has colonies of native frogs, lizards, snails, butterflies, wasps, spiders, earthworms, flatworms, shellfish and plants living far from their natural homes.