The New Nature Read online

  Range expansions are largely the privilege of the winged. Birds, bats and insects are very mobile, easily surmounting the fences, rivers and hostile habitats that hold other animals back. In Victoria horseshoe bats have moved closer to Melbourne by taking over old mine shafts between Kinglake and Mt Disappointment. Rare in Victoria, these bats were previously confined to caves in Gippsland. I’m amazed to think of them wandering west at night and chancing upon old shafts sunk in unexpected places. All up, seven kinds of cave bats in Australia have spread to new habitats by occupying old mines.

  Flying-foxes are also part of this story. In the 1920s fruit farmers were locked into battle with hordes of the screeching spectres winging in under cover of darkness to feast on bananas, pawpaws and other sweet fare. Implored by farmers for help, the government lured Francis Ratcliffe out from Oxford in 1929 to conduct what was arguably the first ecological study ever undertaken in Australia. The affable Ratcliffe roared about on a motorbike meeting farmers and seeking out bat camps. He realised that flying-foxes go south in the warmer months, journeying from Queensland into New South Wales and sometimes reaching Victoria. During winter no bat camps remained south of the Mary River in southern Queensland, although occasional bats over-wintered further south. The story is very different today. Grey-headed flying-foxes occupy permanent camps as far south as Sydney and Melbourne. Black flying-foxes maintain year-round camps in northern New South Wales. Ratcliffe himself detected some ‘natural change’ when a permanent camp appeared at Nambucca in 1932.

  Butterflies also travel well. Orchard (Papilio aegeus) and dinghy swallowtails (Eleppone anactus) have been lured into the Outback by orange and lemon trees around homesteads, and have spread south into Victoria as well. There may be hundreds of other insects buzzing around in unexpected places, but data is difficult to obtain. Queensland fruit-flies attacking orchards in Victoria are one example.

  But not all the species expanding their territories are winged. In Victoria swamp wallabies (black wallabies) have spread well west into the Grampians, Wimmera and mallee regions, far from their wetter strongholds further east and south. During droughts they sneak into gardens and parks for green feed. For animals without wings they’ve done very well. Other marsupials whose ranges are spreading slightly include barred bandicoots in Tasmania and grey kangaroos in western Queensland. In future, given more time, other flightless animals will follow suit.

  Even mosses merit a mention. The limestone around Yarrangobilly Caves in Kosciuszko National Park is much richer in mosses today than in 1906, when ninety-five species were counted. Many of the newcomers have come in from the Outback, their spores apparently blown east by dust storms after tractors tore up the moss beds that once carpeted inland plains. The new species grow well on the paths and clearings made for tourists visiting the caves.

  But it’s birds that epitomise the process of change. The crested pigeon has done more than any other to spread its wings. It was once an Outback bird, not found east of Gunnedah or Goondiwindi and not within hundreds of kilometres of Perth. ‘The chasteness of its colouring,’ Gould wrote in 1865, ‘the extreme elegance of its form, and the graceful crest which flows from its occiput, all tend to render this Pigeon one of the most lovely members of its family, and it is therefore to be regretted that, owing to its being exclusively an inhabitant of the plains of the interior, it can never become an object of general observation’. Today crested pigeons are objects of general observation in Sydney parks, where they peck at seeds in short grass. They visit my garden. Widening their horizons long ago they followed forest clearing east and west, driven on whistling wings by the spectre of drought.

  A flock wandered into northern New South Wales in 1939, but ‘topknots’ (as many folk call them) only became a regular sight in Brisbane in the 1970s and in Sydney a decade later. They appeared on farms north of Perth in 1964. Gould wrote: ‘The locality nearest the coast-line that I know it to inhabit is the country near the bend of the river Murray in South Australia.’ Today crested pigeons breed on islands. They are still spreading. The New South Wales south coast was claimed in the 1980s, Picton in 1982, Ulladulla in 1984 and Moss Vale in 1986. Canberra and Melbourne are the latest conquests. Crested pigeons have triumphed because people have laid bare the land. A city park with scattered trees looks through pigeon eyes like Outback woodland.

  Galahs also came east and west. I remember as a child my first wild sighting of these pink and grey parrots, a company floating high over the road on Brisbane’s northern fringe, uttering a cry I had known only from pet shops. Galahs then were a source of awe; now they are common urban birds. On some southern beaches they harvest exotic sea rocket seeds, disturbing the peace where rare little terns nest. When a galah meets a tern he raises his crest, like a country cocky doffing his hat on a first visit to the seaside. The terns are not grateful. Already flustered by beachgoers and dune buggies, the last thing they need are exuberant greetings from colourful Outback birds.1

  Sydney’s mangrove gerygones, tiny birds, are also new arrivals. A century ago they weren’t found in New South Wales at all, but soil erosion has helped them spread south from Queensland. Mangroves like the silt that erodes from farms and gathers in estuaries, especially downstream from dams that hold fresh water back. Extra growth of mangroves apparently encouraged the birds south. A gerygone was first seen in Sydney in 1982.

  Bird changes are easy to track because their past ranges are well known. Birdwatchers love listing birds when they travel, and their old lists can be found in the journal Emu. In 1903 Lawson Whitlock spent several weeks around Mogumber, a township north of Perth, and his list caught the eye of Dom Serventy and W. Loaring, who went there almost fifty years later, in 1950, to compare. I went there myself almost fifty years later still, in 1998. In Whitlock’s day there were no galahs, singing honeyeaters, white-fronted chats, crested bellbirds or regent parrots, all of which were seen in 1950. On my quick trip I didn’t see the last two birds but I did spot three newcomers: crested pigeons, straw-necked ibises and yellow-billed spoonbills. Whitlock saw no galahs in three weeks, Loaring and Serventy saw several in one week, and I saw many in a few hours. Contrasts like these can be drawn almost anywhere.

  Range changes are often driven by hardship. Arrival times of birds in south-western Australia often match droughts somewhere else. Sydney’s galahs arrived with the 1941 dry, and the appearance of crested pigeons often coincided with failed rains elsewhere. When the droughts end the birds remain. Why go back? An extraordinary number of Outback birds now live along our coasts, including cockatiels and zebra finches.

  Some bird ranges are expanding as truly natural events. In Western Australia the southward spread of terns and other seabirds – eight in all – is attributed to a natural strengthening of the warm, south-flowing Leeuwin Current. On Sugarloaf Rock I’ve seen tropic-birds – clean white birds with red ribbon tails – that expanded south of Perth in the 1960s as the current grew. Other changes defy explanation. Fairy terns have spread into New South Wales and now hybridise with rare little terns. Concerned biologists don’t know if this is a natural or a human-induced process.

  In some regions the variety of birds has increased as a result of range expansion. On Kangaroo Island the original bird guild still survives in the national parks (apart from an extinct dwarf emu), while twelve newcomers have claimed the pastures and dams that stand where heaths and mallee once grew. Sulphur-crested cockatoos came in 1905, galahs in 1913, black-shouldered kites in 1934, wood ducks in 1950, brown quail in 1959, freckled ducks in 1971, and so on. Canberra has gained many birds, and gains around Sydney and the Perth region probably exceed losses. I’m not at all pleased about this, as the losses have been terrible. The destruction of so much Kangaroo Island heathland for sheep was tragic.

  Changing ranges are a global phenomenon. In North America thirty-five birds have expanded their frontiers on the western side of the continent alone. Anna’s hummingbird does so well from garden flowers and sugar feeders
it now breeds up in Canada. The warmth of American cities allows birds to remain north in winter. In South Africa 30 per cent of birds in the Fynbos region are newcomers, including the guinea fowls, blue cranes and Egyptian geese I’ve seen strolling about on farms. In South America monk parakeets have invaded once treeless plains by nesting in Australian gum trees grown around homesteads. In England the rock-loving black redstart boomed after World War II by adopting bombed buildings as habitat.

  How to interpret all this? As nature triumphing over change, or as humans stuffing things up again? Probably it’s a bit of both. Sometimes, but not often, changing ranges helps secure a bird’s future. Yellow chats, cute little birds that have disappeared from some regions, have invaded the Queensland Outback by claiming bulrush beds lining artesian bores. The bulrushes (Typha domingensis) have themselves invaded, their fluffy seeds wafting in from distant waters. Bore drains thus help yellow chats secure their future in Queensland, where they are rare. The regent parrot, also rare, has also made gains to offset losses. For grey-headed flying-foxes, losses and gains tell the same story – the population has shifted southwards while declining overall.

  All too often we see the same few birds succeeding everywhere – galahs, corellas, crested pigeons, wood ducks – and many other birds declining. Sydney, for all its gains, has lost rare ground parrots, plains-wanderers, and many more. Some of our woodland birds are fading away, for reasons that often aren’t clear. The losers outnumber the winners, which by acting aggressively sometimes worsen their plight.

  1  Other Outback birds that have come east include the banded lapwing, red-rumped parrot, white-plumed honeyeater, striped honeyeater, double-barred finch and white-backed swallow.

  ‘There are no foreign lands. It is the traveller only who is foreign.’

  Robert Louis Stevenson

  Animals are not as tied to place as we think. The kinds of shifts we’ve just considered go on even across international boundaries. In New Zealand, where the winds come from the west, Australian birds are invading and Australian seeds blowing over. Forests and fields are growing more colourful as more and more Australian birds, butterflies and orchids move in.

  Silvereyes made the crossing in 1856. At first farmers cheered on the little green birds that cleaned out mischievous aphids and scales from their orchards. But delight became dismay as summer arrived and the birds advanced to sweeter fare, exacting payment for their services by stripping ripening fruit. Settlers then rued these ‘blight-birds’ for the ruin wrought to cherry groves. The more welcoming Maori called them ‘tahou’ (stranger) and added them freely to the cooking pot. Ethnologist Elsdon Best remembered how ‘the hardy Tuhoean bush-folk crunch up the birds – head, bones, inside, remaining feathers and all – with great zest’. He saw many thousands ‘killed, plucked, cooked whole without cleaning, and preserved in fat – in kerosene tins’. That was late in the nineteenth century, and silvereyes were obviously prolific by then. Today they outnumber all of New Zealand’s original forest birds. They play a pivotal role in forest ecology, spreading the seeds of native trees in place of older, vanished birds.

  Australian swallows now rule New Zealand skies. They came in the 1950s and liked what they saw. Masked lapwings (spur-winged plovers) arrived in the 1930s and now patrol farms and fields with a proprietorial air. The 1940s brought in spoonbills and herons, the 1950s coot and dotterels, and night herons have colonised since then. Add in a sprinkling of shelducks and grebes found on scattered wetlands and the tally of new birds is impressive.1

  Birds lobbing into New Zealand are protected as ‘native’ fauna alongside kiwis and tuataras. But how native are they? These birds do best on farms and modified wetlands, prospering where axes and dams have remade the land and dominating habitats New Zealand birds avoid. Arriving was natural; surviving was not. Our birds have been blowing in to New Zealand for millions of years, but usually without lasting long. In the past only forest-dwellers and shore birds had much hope of surviving. Tuis (enormous honeyeaters) and kiwis both evolved from ancient Australian blow-ins. Silvereyes are forest-dwellers but they find New Zealand’s rainforests too barren in winter, whereas farms and gardens yield richer fare. They probably came to New Zealand straight from rural Australia, having already learned the skills needed for life on farms. The same was surely true of swallows and lapwings. Their numbers had risen back home, making conquest of New Zealand more likely. New Zealand was effectively invaded by Australian farm birds seeking new farms.

  The winds from the west also bring New Zealand improbable visitors. Orb-weaving spiders (Nephila edulis) blow in, the hatchlings apparently wafting over on gossamer strands before swelling into huge, hairy-limbed arachnids that alarm the locals. Butterflies waft over as well, on a journey that may take three days, sometimes arriving in immaculate condition. Painted ladies, common eggflies, and lesser wanderers are regular visitors, a few eggflies arriving most years. New Zealanders call them ‘blue moons’. Some forty kinds of moths and butterflies have crossed a sea more than 2000 kilometres wide. Most blow-ins don’t last through winter, and only a few have become established. The common blue (Zizina labradus) is now New Zealand’s most common butterfly. Their caterpillars fatten on clover meant for cows. They are Australian insects living in New Zealand on European plants. The same is true of the long-tailed blues (Lampides boeticus) found breeding on exotic pea plants. Owl moths (Dasypodia cymatodes), on the other hand, feed only on wattles brought over from Australia.

  The most unlikely insect immigrants are minute wasps. In Australia they pollinate fig trees, each kind of fig relying on its own unique wasp a couple of millimetres long. Australia’s Port Jackson figs (Ficus rubiginosa) and Moreton Bay Figs (F. macrophylla) were growing in New Zealand parks last century, but without their wasps they set no seed. Then Port Jackson wasps (Pleistodontes imperialis) blew in during the 1960s and Moreton Bay wasps (P. froggatti) some thirty years later. Each year there are twenty-one days when the winds offer a passage time of two or three days at 300–1000 metres altitude. The wasps only live two or three days. We may marvel at these flimsy things, barely visible to our eyes, hatching on figs somewhere in Australia, blowing 2000 kilometres over cold seas, then falling to rest on a fig in New Zealand. They locate figs by scent. The trees are now setting seed and turning into weeds, Port Jackson figs proving especially invasive on Rangitoto Island. In some regions they’ve been banned from sale.

  These plants became weeds via a natural event – a wasp catching a breeze – but the wasps had been blowing over the seas for millions of years without ever reaching anything to eat. There are now seven species of Australian insects found on figs in New Zealand, including a wasp parasite one millimetre long. New Zealand gained new birds because artificial habitats were made, and new wasps because their native foods were imported.

  The seeds of orchids resemble specks of dust and, like wasps, they blow unbelievable distances. Ten Australian species have colonised New Zealand over the past century, including donkey orchids and sun orchids. A favoured habitat is manuka (Leptospermum scoparium) scrubland, which grows on old European and Maori farms. Another habitat is tussock grassland, which was extended by Maori fires. Here again we are seeing assisted invasions. The seeds were presumably blowing over tens of thousands of years ago, but not until forests were cleared could they sprout and grow.

  New Zealand statistics on tree clearing are telling. A third of the forest was destroyed by Europeans, another third by the Maori before them. The Maori wielded fire with zeal, scorching back rainforests to create farms, grasslands and fernbeds (producing edible bracken stems). ‘The vast open plains of Canterbury and Otago look natural,’ notes Carolyn King, ‘but there are weathered stumps lying among the tussocks, and layers of charcoal in the soil, which can be dated to the twelfth and thirteenth centuries A.D.’ Captain Cook saw many abandoned farms when he explored Queen Charlotte Sound, scrawling in his journal in 1773: ‘we find many forsaken habetation in all parts of the Sound . . .�
� If ten birds invaded New Zealand after the English came, others must have colonised earlier in response to Maori clearing. Evidence for this is surprisingly easy to find. New Zealand is very well endowed with Quaternary bird remains. Bones accumulated in swamps and caves, under roosts of extinct laughing owls (wiped out in 1914 and no longer laughing), and at old Maori camps (they ate most species). What the bone-handlers don’t find, in pre-Maori sites, are the remains of five birds found in New Zealand today: harriers, swamphens, bitterns, shovellers and stilts.

  Swamp harriers are today New Zealand’s most common bird of prey. They float over fields and perch on posts as if farms were made to serve them. They seldom enter New Zealand’s forests. In Australia they are seasonal migrants, and I can easily imagine some vagrants veering off course and coming upon Maori fields, then hunting the quail (now extinct) that fed there. Swamp harriers offer yet another example of an Australian animal doing best in a humanised landscape, in this case in another country. Australian birds were adapting to agriculture in New Zealand long before they could do so here.

  Purple swamphens (pukekos) invaded New Zealand only three hundred or so years ago. They soon became pests, raiding Maori sweet potato plots at night. Ironically it was Maori land use that gave them a home. The Maori razed trees fringing swamps and streams, allowing bulrush (Typha orientalis) thickets to take their place, creating ideal shelter for pukeko, and also for Australasian bitterns, another newcomer. The Maori harvested bulrushes for food and thatch and probably promoted their spread. Fossil expert Richard Holdoway believes pukeko only colonised because Maori hunters also culled competing birds – takahe and rails.