Flight Paths

IN THEIR BEAUTY, they would come in multi-coloured waves, shimmering through the landscape. Alone, each butterfly seemed fragile, erratic, purposeless; but en masse they were coordinated, resolute, committed to a timeless common goal. Seasonally, migrations of green swallowtails, caper whites, painted ladies passed through the village in the Australian Alps where I lived as a boy. Their quest seemed beyond their flimsiness. They delighted and transfixed me: where had they come from, where were they going, would they make it? One year, delusional, we spent weeks netting hundreds to attach tiny numbered labels to their wings, hoping that someone somewhere would resight them and help answer the questions that entranced me. Mostly, the butterflies we tagged would fly in burdened circles, labouring, fluttering to the ground. And never were any of them reported again. I’m sorry now for that misadventure.

Some years, the alpine ash forests around us would fill with outbreaks of phasmids, large stick insects – the males elongate and brown, the females fat and green – too heavy to fly. They ebbed and flowed to a rhythm remote to us. In the forest, their frass would fall to the ground like rain; in their hunger and their plenitude they defoliated large patches of forest until the foresters sent light planes, spraying the hillsides with poison.

Birds moved through. In winter, the currawongs came, their haunting calls ringing through the mist. Those calls still transport me back to my childhood. In autumn and spring, weeks of flame robins in small restless groups; honeyeaters and silvereyes in tight flocks of hundreds flashing through the canopies, navigating the mountains, their thin continuous calls reinforcing the cohesion of the group, the communal purpose. Some years, the migrating flocks crashed against the sudden storms, and afterwards the forest floor was littered with their tiny spent bodies.

These scenes are played out, in infinite variations, almost everywhere across our backyards, continents, rivers and oceans.

WHEREAS HUMANS mostly live in one place, many animals must move – needing to work the landscape to chase the continuously shifting patterns of food, or to track the climates in which they can survive.

Our land is crisscrossed with lines we cannot readily see, marking the routes of dispersing animals, the pathways they must travel. Largely because they too worked, read and respected the dynamism of the lands, these pathways have parallels with the songlines and trading routes of Indigenous Australians: they tell of myriad meaningful ecological and spiritual connections, of a landscape in which distant points are part of the same deeply etched story, of an intricate network connecting all places.

IN AUSTRALIA, the patterning of lines is more complex and diffuse than other places. Most other continents are characterised by strong and long latitudinal gradients with endpoints of deeply contrasting climates and sharp seasonality. On those continents, migration tends to be a regular long beat, a six-monthly reverse cycle of fleeing the cold, chasing the sun. In contrast, much of our continent is governed by erratic phases of rain and drought, and we do not have such strongly defined latitudinal transitions in climate. Consequently, many species – birds especially – disperse irregularly, eking out frugal lives in the dry times and exploiting the good, irrupting across the landscape. Locusts do this too, although broad-scale poisoning campaigns in ‘plague’ years now dampen the rhythm. The archetype is the banded stilt, a beautiful waterbird that may wait for decades without breeding, until rains in inland Australia fill the shallow lakes on which its life depends. It is a perilous strategy.

The flock bronzewing is another example of a species attuned to our continent’s erratic pulse. Its stronghold is the grasslands of the Channel Country and Barkly Tablelands of inland Queensland. In dry years, it is uncommon and restricted, but following good rains, it can form vast travelling flocks, wheeling across the inland skies, settling where the grasses have seeded. The historic records speak of its spectacular numbers: in 1902, in the journal Emu, T Carter wrote of ‘enormous flocks … in countless thousands. The roar of their wings was like the noise of heavy surf breaking on the beach’. Lewis, in 1922, wrote that ‘Sturt’s Plain was alive with flock pigeons. From some distance they looked like clouds of smoke ascending here and there … Never before have I seen such numbers of feathered game.’ Although I have been fortunate to see this marvellous bird in flocks of many hundreds, the immense numbers are no more, and may never be again. Now, their grassland habitat is cattle country; the refuge areas on which they depend in the dry years grazed and degraded.

NOMADISM IS A FEATURE of many Australian birds. It is particularly marked in nectarivores – birds (and some mammals) that feed mostly on nectar and pollen. Instead of distinct north–south movements, they track the kaleidoscopic patterning – fluctuating in time and space – of flowering trees across an ever-changing landscape. For nectarivores such as swift parrots and regent honeyeaters, there were strongholds in this wandering, particularly the vast areas of ironbark woodlands inland from the dividing range in Victoria and New South Wales, where the seasonal nectar resources were rich and mostly reliable. No more; the woodlands are now mostly cleared and fragmented, habitat disconnections making dispersal a lottery with diminishing returns. We have severed the lines on which such species depend and, as a consequence, these species are now threatened, their populations rapidly decreasing. They wander still, but too often their searches for flowering trees end bleakly, the bounty of the landscape broken. Ecology is all about interconnections, among places and species. We are losing these nectarivorous birds, and with such loss, their functions as important pollinators. As a result, our landscapes become less diverse, less healthy.

Of course, not all animal dispersal in Australia is so irregular. Indeed, many birds migrate along largely fixed routes, and some shift between Australia and other continents. Each austral summer, the swifts arrive, surfing on the storm clouds, cruising easily from their breeding haunts in Siberia: their flight a marvel of power and agility. From Asia, each year, come curlews and sandpipers, hugging the coastlines. Dollarbirds, bee-eaters and cuckoos make long-distance annual migrations, and in many places their welcome appearance heralds our summer: I still get a thrill when I hear the first koels of the season, their call both beautiful and maddening. For some migratory birds, these lines and links have been mapped and designated as ‘flyways’: the curlews, along with many other shorebirds, use the East Asian–Australasian Flyway.

Migration is a gamble. It can work only if there is safety at the point of origin, at the destination, and at stopping points along the transit: such reliance on many places increases risk. So, although we may (arguably) protect curlews or plovers in their swamp, mudflat and beach haunts around the Australian coast, such protection will be subverted if the coasts of Korea and China, long used as staging points to break up the 20,000-kilometre annual round trip, are now being transformed and degraded; or if large numbers are shot at their breeding grounds in north-eastern Asia. These are weak points in the chain. Many of the world’s long-distance migratory birds are declining. Mostly, this is driven by habitat loss in part of their range, especially the tropics.

The situation for some of these migrants is not without hope, or lessons. Many of these migratory bird species are afforded particular conservation status through global and bilateral treaties recognising joint responsibility. Australia has such agreements with China, Japan and Korea. Such treaties help bind nations to work together for conservation. Perhaps even more impressive are the cooperative networks of non-government organisations and community groups that have now been established to celebrate and help coordinate protection of these migratory birds across the extent of their migrations. These birds and the lines that they travel can link peoples, places and cultures, making us all more aware of what we share.

THE ORANGE-BELLIED PARROT is now one of the world’s most threatened species. Over the past twenty years its population has wavered between about twenty and 200 individuals. This small parrot breeds only in south-western Tasmania, then migrates across stormy Bass Strait to spend winter in the muchfragmented habitats of coastal Victoria, returning across the sea again in spring. It must be a daunting challenge. Especially so for the juvenile birds, who depart the breeding grounds after the adults have left. Their crossing is made without the benefit of previous experience: the route they fly is entirely new to them. Nature is full of astonishing mysteries, of miracles.

PLANTS MOVE TOO. It is not so directional, so active, so purposeful, so visible; and mostly it is a once-in-a-lifetime experience. The seeds of many coastal plants, such as coconut palms and mangroves, are buoyant, an exquisite evolutionary asset that allows them to float thousands of kilometres across the ocean. Many drift and fail, but some succeed in washing up on islands, establishing new populations on distant shores. I lived for a time in the paradise that is Christmas Island (though for others, it is a desolate prison). On one small beach, botanists found seeds and fruits of more than sixty plant species deposited by the waves. These voyages across the seas are not entirely random: the seeds move along lines etched by ocean currents.

Other plants use animals. Burrs trap themselves in fur, hitching rides on unsuspecting animals. Often, the relationship is cooperative. Flying-foxes, as well as pigeons, koels and many other birds, consume the fleshy fruits of many plant species and excrete the seed elsewhere. In the case of flying-foxes, this carriage may be tens of kilometres from the parent plant, allowing the species to establish new populations far from their parent. Narrow mutualism is risky – the fate of one species linked irrevocably to another. Some rainforest trees in tropical Queensland depend, in part, for their dispersal on the only native animal capable of eating their large fruits, the cassowary; where cassowary populations have diminished, the options for seed dispersal wither. Most likely, when the mihirungs – those wonderful giant flightless birds of central Australia – became extinct about 30,000 years ago, their loss had wide ecological ramifications, leaving at least some large-fruited plants without their long-established primary means of dispersal.

LOSSES CONTINUE. With each, the ecological fabric of our land tears. The lines connecting our landscapes weaken; our nature thins; our collective memories of previous wonder fade. We have disrupted these links too much, and the ecological weaving of this country is unravelling.

The butterflies that moved through my boyhood home were impressive, but their numbers are a pale shadow of the past. Professor Frederick McCoy, in Natural History of Victoria (1878–1890), noted one of these species, the Australian painted lady, ‘in extraordinary numbers for two or three weeks … almost darkening the sky … and filling the air on land from the northern part of the colony down south to Melbourne … The newspapers mentioned the stoppage of trains in the tunnel on the Castlemaine Railway, from the masses of bodies of these insects crushed lubricating the wheels to such an extent that they could not bite the rails as they turned, and came to a standstill …’ Such abundance is no more. Likewise, the yellow-faced honeyeaters that passed me in flocks of hundreds on migration were a small marvel, but a report by John Liddy in a 1966 edition of Emu tells of the same species – ‘A blizzard of birds was passing’, with estimates of between 100,000 and 300,000 birds passing in one hour.

These landscape lines – so vital for so many species – have long been mysteries to us, unseen and misunderstood. But, as technology advances, we are learning more, revealing their intricacy. Large amounts of observations can be aggregated, automatic data loggers can report whenever a tagged animal passes nearby, and arrays of increasingly sophisticated camera traps and sound recorders can detect animals remotely, and continuously, over long periods.

The most profound breakthroughs are with ongoing advances in transmitters and satellite tracking. The transmitters, when attached to an animal, send signals to orbiting satellites that reveal the animal’s location. The transmitters are getting lighter, smaller, more durable and precise. It is possible to follow the movements of much smaller animals, for longer and more reliably, with little burden for the animal carrying them. The results are astonishing, the revealed lines beautiful.

NATURE IS DIMINISHING; the world increasingly modified. We ignore, tear up or are ignorant of the lines that are so critical for so many other species. Climate change will further fray these networks. What can we do? We can help rebuild broken lines, through joining community groups that undertake revegetation, especially where plantings can reconnect now severed landscapes. Even better, we can advocate to halt the ongoing clearing of our native vegetation: in the past twenty years, about 8,000,000 hectares of habitat for Australia’s threatened species was cleared. Such loss obliterates the ecological connections on which so much of our world depends. We can urge for conservation of parts of the landscape that provide refuges to species in otherwise inclement times. We can join citizen science projects that, with every contributed record, help find and understand travel lines, so that they can be better protected.

We can marvel still as our gardens host, for a time, animals journeying to more distant parts, and recognise the need to see the world as they may do, to look after them when their lives intersect with ours, and when they move beyond it. We need to recognise that where we live is part of a vast environmental network, with lines that connect us to many other places. Last week, it was grey fantails drifting across my garden, notwithstanding their profound incapability of flying in a straight line. Next week, it will be something else. Being here; then being elsewhere.

All across the landscape lie lines hidden from us. The wonder and mystery of these lines, and of the animals that travel them, fascinated me when I was young; they entrance me still; they always will. For in these lines there is a connection to the lives of others, a pathway to other worlds.

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Post cover image caption: Xavi Bou. Ornithography # 150. Grand Teton National Park, USA. Barn swallows hunting insects in the last hours of the day.