The New Nature Page 7
The idea of ecosystem engineering may help explain why so many of our smaller mammals became extinct. We’ve lost more species than any other continent – three wallabies, three bandicoots and several rodents, with others surviving only on offshore islands. Some years back, Andrew Burbidge and three colleagues went visiting remote Aboriginal communities in the hope that some of these animals had survived. They sat with elders, passing around old museum skins. Their quest was clever, but they came thirty years too late. No rediscoveries were made – not even one – but many elders volunteered priceless ecological data. Burbidge and colleagues recalled one meeting: ‘When all the different skins had been spread out on a hessian bag, a Ngaanyatjarra man said, “But you haven’t got the Kuluwarri there.” The Kuluwarri? This was our first clue that the enigmatic Central Hare-Wallaby, known to science from only a single skull collected by the explorer Michael Terry near Lake Mackay [in the Northern Territory] in 1931, had once actually lived in W.A.’ Kuluwarri was recalled as a soft furry being who dozed by day under spinifex and nibbled grass and seeds at night. He lasted in the deserts until the 1960s. All we know of him comes from elders at more than thirty remote stations.
When Burbidge asked why these mammals had vanished, a strange story emerged. Most elders blamed not cats, foxes and rabbits, not cows and sheep, but themselves. The animals vanished when Aborigines forced onto missions could no longer conduct increase ceremonies and burn their land. ‘It seems likely, therefore, that changes in burning patterns caused the major decline in the desert mammals,’ Burbidge concluded, ‘and the introduced predators then finished off most of the remaining pocket populations.’ What this implies is that Aborigines maximised diversity by mosaic-burning the deserts. Kuluwarri and his kin needed patchwork quilts of burned and unburned land, which people alone could provide. But this idea makes no obvious sense. We know from fossils that these animals existed long before people came. How did they fare then?
Tim Flannery believes bushfires were originally suppressed by big mammals trimming back vegetation. Mosaic burning therefore replaced megafaunal browsing as a means of keeping fuel loads low. When Aborigines were evicted from their lands, fuel accumulated until raging fires could roar through, converting kuluwarri’s home to ash. In today’s Outback, lightning fires can travel unhindered across the flat terrain. A 1922 fire apparently went a thousand kilometres from Oodnadatta to Tennant Creek. But Tim’s idea has its critics. The main fuel in bushfires is grass, yet we know from their teeth that most megafauna were browsers, taking leaves from shrubs and trees rather than cropping grass. After their demise, extra growth of shrubs and trees should have shaded out some grass, reducing instead of increasing the fire risk. Dense shrublands don’t burn well, as farmers well know. Furthermore, the megafauna would not have eaten much spinifex, a very tough grass that offers little sustenance. It can prove amazingly flammable, a clump I once lit just about exploding, and I can’t believe it was ever grazed too low to burn.
Fire matters to the rufous hare-wallaby (or mala), which by 1978 had nearly vanished from Outback Australia. B. Bolton and Peter Latz combed 2300 square kilometres of the Tanami Desert to find the two last groups, handfuls of animals living by a stock route. Every winter the stock route was torched. The malas hid in thick, unburned areas and fed by night on spinifex reshooting after fire. They survived because the stock route was managed like Aboriginal land. The Tanami mala have since vanished, in ways that defy easy interpretation. One lot was hit by foxes and drought, the other by wildfire. Biologists are now mosaic-burning the dunes and reintroducing malas, but feral cats hinder their work.
Theories about mosaic burning are contentious. Mala and other rarities survive on some islands where Aborigines don’t burn. Freedom from foxes seems crucial here, and many experts blame the mainland extinctions on a lethal cocktail of rabbits, foxes, cats, stock, goats, fire and drought. Even so, there can be no doubt that in many parts of Australia human-lit fires are essential acts of engineering to maintain biodiversity.
There’s even a big lizard in the spinifex deserts that likes mosaic burning. The great desert skink (Egernia kintorei) is rare and declining, and survives mainly where Aborigines still burn the land. It’s another example, like the orange-bellied parrot, of a rare species in a remote place that depends on people. Nature is seldom as natural as we think.
Australia has been shaped by a succession of large engineers. Dinosaurs were followed by large mammals, then by people – first Aborigines, then Europeans and their livestock. Tim Flannery says, ‘We (Homo sapiens) are the last of Australia’s megafauna. We are the ecological equivalent of Diprotodon, Thylacaleo and all the rest.’ Some of our impacts have been comparable.
The idea of ecosystem engineers has its flaws, but I like the way it classifies people with buffalo, beavers and other beasts, instead of marking us out as unique – and uniquely destructive.2 (We are extremely destructive, but that’s because there are too many of us, not because our actions are inherently ‘unnatural’.) It also provides a way of equating human actions – like burning – with animal impacts like grazing. It makes sense of the fact that brown snakes like paddocks and bell-frogs like dams. It’s a way of saying we are really just animals. And given that animals often coexist closely, it helps explain why other animals (and plants) often choose to live with us. We are a large, abundant mammal that concentrates nutrients and water and shapes landscapes dramatically. Animals and plants inevitably respond to these changes, as the next two chapters show.
1 Because birds have good colour vision but usually no sense of smell, one can assume that big sombre fruits with alluring aromas evolved to attract large mammals.
2 The ecosystem engineers theory has a problem of scale. For an ant, the scratchings of every mouse and lizard count as major engineering feats, implying that most animals are engineers. The theory also fails to accommodate abiotic engineering generated by fire and floods.
‘Shit happens’
Tom Hanks, Forrest Gump (1994)
Rising up from swirling seas well south of Tasmania is a lump of rock called Pedra Branca. Almost devoid of plants, this 2.5 hectare dome is the last home of a rare reptile, the Pedra Branca skink (Niveoscincus palfreymani). This animal survives only because gannets come to the rock to breed. The adult lizards live entirely on lumps of fish dropped by gannets. Pedra Branca skinks are waste-dependent, relying almost entirely on the scraps and vomit of birds.
Dung beetles also depend on wastes, as do certain caterpillars that eat koala and parrot droppings. There are also plants (ornithocoprophiles) that do best in the fouled earth of seabird colonies. On Barrier Reef islands, black noddies (birds) nest on the branches of pisonia trees (Pisonia grandis), both fertilising the trees and spreading their sticky seeds. When noddies abandon islands, the trees often waste away from want of fertiliser. In South Australia I’ve swum out to a rock platform where penguins and seagulls breed, to find leafy peppercress (Lepidium foliosum), a rarely seen herb that only grows where seabirds gather.
Wastes often matter to wildlife. This holds true especially in Australia, the least fertile of lands, where the main waste-producer is Homo sapiens. Our faeces and scraps sustain vast communities of animals and plants. They influence ecosystems as far away as Siberia and South America. Watching where our wastes go is one way of discovering how important we are to wildlife; of seeing how other species exploit the opportunities we create.
Sydney’s sewage runs to the sea through three deepwater outfalls. These are tunnels two to four kilometres long in the bedrock of the sea floor, with lines of diffusers to disperse the fine waste. The Bondi outfall, the smallest of the three, pumps out 1700 million litres of toilet and kitchen muck each day. Surveys conducted after the outfall began pumping show that Sydney’s toilet bowls and sinks feed plenty of sea life. In the fine sediment around the diffusers biologists found increased numbers of shellfish, worms and crustaceans. They found more bottom-dwelling fish, mainly those that eat
these creatures, including flounder, red gurnard and bastard trumpeter. Trawlers often net these fish, and so some of Sydney’s sewage finds its way back into the human food chain. When you buy flake from a fish and chip shop you may well be eating the fins of a searay that fed around an outfall. Nick Otway, who was in charge of the surveys, suggests that ecological zones may form around outfalls – an inner zone where a few highly tolerant invertebrates crowd together, surrounded by a more diverse zone where many species benefit from medium nutrient levels, beyond which numbers drop away to natural levels. Sydney’s waters are so nutrient poor that sewage really matters, although only certain species prosper and others move away.
In the years before these tunnels were made, most of Sydney’s sewage ran out through three cliff-face outfalls – at Bondi, North Head and Malabar. Believe it or not, between 1916 and 1972 the sewage from Malabar sustained vast numbers of a now-endangered bird, the wandering albatross. In his article ‘Sea-birds and Sewage’ (1955) Keith Hindwood told how this sewer served factories between Sydney and Botany Bay: ‘The industries served within the area outlined include fellmongers, tanneries, wool scours, gelatine and breakfast-cereal factories, various boiling-down works, small-goods and other food-processing plants and, what is probably the most important from an ornithological standpoint, the abattoirs at Homebush.’ From here flowed 30 million gallons of sewage daily. Albatrosses were gulping down ‘butchers’ wastes from the abattoirs and fatty matter resulting from the treatment of sheep-skins and hides’. Each sheep yielded 0.3 kilograms of waste, and each pig, calf and cow 0.5 kilograms, amounting to 1.8 tonnes of lard, membrane and other muck each day.
Radio-tracking studies show that albatrosses seldom cross continental shelves, but when seas were calm the Malabar plume served as a river of lard that lured the big birds right up to the cliff. Bird-bander Harry Battam remembers a column about sixty metres wide running out to sea for a couple of miles. ‘On a clear day you could see the sewage plume going right out to the horizon,’ he told me. Albatrosses have a keen sense of smell, and they could no doubt smell the offerings.
‘Albatrosses are gorge feeders, like dogs,’ Harry told me. ‘They stow away two to three kilos at a time, then sit all day and digest it.’ He remembered seeing hundreds of the big white birds sitting in the plume among faeces, condoms and toilet paper, digesting sewage. As many as 700 birds came to Sydney to feed, by Harry’s estimate the largest concentration of these albatrosses in the world. Now they are endangered, with a global population of 43 000. Banding studies showed that albatrosses came to Sydney from most (if not all) of their breeding colonies, including Macquarie Island, islands south of New Zealand, Crozet Island (south of Madagascar) and islands east of South America. Birds from the farthest outposts were flying up to 30 000-kilometre round trips to fatten on Sydney sewage. Albatrosses breed every other year, regaining lost weight in the intervals, and abattoir waste was obviously ideal for replenishment – much better than the dead cuttlefish and squid they usually eat.
When Sydney adopted better sewage treatment, everyone cheered, but no-one had albatrosses in mind. Their numbers plummeted locally. Birds from South Georgia and Prince Edward Island, the farthest outposts (beyond South America), stopped coming. Not worthwhile just for squid. Albatrosses are now high up on endangered lists, and everyone blames long-line fishermen (albatrosses die on the hooks) but Harry – and colleague Lindsay Smith – have a different idea. They suspect sewage treatment is partly to blame, and said so in a report to the Australian government.
Those abattoirs in Sydney also fed black-browed albatrosses, southern skuas, northern and southern giant petrels (up to 300 at a time) and gangs of gulls. No other city below the equator fed so many big birds. The largest affluent source of effluence in the south, Sydney was the ultimate food trough.
In the 1980s the abattoirs closed, and the Olympics committee claimed the Homebush site. Green and golden bell-frogs moved into the abattoir’s old nutrient settling ponds. One endangered species (the albatross) suffered as another (the frog) gained.
Much of Brisbane’s sewage exits at Luggage Point, where currents convey it north. Nearby mudflats attract hosts of waders, especially bar-tailed godwits, curlew sandpipers and great knots. Sewage evidently feeds the mud-loving creatures these birds eat. Back in the 1980s, when sewage was poorly treated, Luggage Point was the busiest hang-out in the bay, often attracting 15000 waders and sometimes almost twice that. Numbers of sandpipers and knots peaked in autumn, just before their epic flights north to Siberia where they breed. They go farther than most waders, sewage-fattened worms fuelling their migrations. Sandpipers nest on the Arctic tundra amidst melting snow, leading their chicks to bogs to feed. Before leaving Australia they lay down fat quickly – up to 3.9 grams a day – and they arrive in the tundra emaciated. I like to think that by flushing my loo I help these birds reach Siberia. Great knots were seldom seen around Brisbane in the 1960s, but twenty years later there were up to 2500 roosting in the bay. I have helped wader expert Peter Driscoll cannon-net these birds for banding. Luggage Point no longer attracts great hosts of waders; knot numbers have plummeted. The evidence is circumstantial, says Peter, but he blames improved sewage treatment.
Half of Melbourne’s sewage is fed into a vast complex of settling ponds at Werribee, 35 kilometres west of the city on the edge of the bay. Melbourne in the 1800s was a city that stank. Wastes were dumped into open street channels that fed into the Yarra, which served as both water source and sewer. Clement Hodgkinson, writing for a senate inquiry in 1852, complained of backyards with ‘more astounding accumulations of putrescent substances and rubbish of all kinds, than I ever inspected in the very worst parts of dirtiest English and Continental towns’. He told of buildings with foundations ‘greatly injured owing to the saturation of the subsoil by liquid excrementitious matter’. Melbourne’s death rate from cholera and dysentery was notorious abroad.
A Royal Commission in 1888 proposed that a proper sewage farm be developed. The Werribee land offered the advantages of low rainfall and porous soil. The first Melbourne homes were hooked up in 1897, a pumping station (today’s Scienceworks Museum) feeding the waste west. Lagoons developed during the 1930s now stretch over 1500 hectares. Werribee was advanced for its day, the treated wastes fertilising paddocks grazed by thousands of cows and sheep. Sales of meat and wool defrayed the running costs. This is probably the world’s only sewage plant with its own shearing shed. (It also has a football oval, a church and a school.) Each day it takes 500 million litres of muck (toilet, kitchen and some industrial waste) from more than a million people in Melbourne’s northern, central and western suburbs.1 Werribee is heaven on earth for birds – and for birdwatchers. The lagoons and mudflats teem with waterbirds and waders. In a count of Victorian waterfowl in 1992 Werribee came first out of 659 wetlands for numbers and variety of waterfowl. At times half of all the waders in Victoria and nearly 20 per cent of ducks crowd around its dubious waters. It’s a major refuge for Outback ducks during drought. Bird-counters have totted up 100000 ibises there, a couple of thousand great crested grebes, 1000 cormorants, and hundreds of other birds. Vagrants from Asia turn up regularly, and the tally of bird species exceeds 250. The pooey pools are protected under the international Ramsar Wetlands treaty. Part of Werribee became a sanctuary back in 1921, and in 1983 it was declared by the World Conservation Union a ‘Wetland of International Importance’. It is now listed under six international treaties.
I revisited the Western Treatment Plant (as Werribee is properly called) recently with ornithologist Rohan Clarke. We drove past fresh settling ponds that were inky, stinking, and birdless but for a few gulls. The ponds further on, holding older and cleaner water, were busy with birds, mainly ducks. Two ponds are kept shallow for waders and one of these, 55 East Conservation Lagoon, sheltered hosts of sandpipers and stints. Here we ran into Bob Swindley, a retired plumber who does regular bird counts. ‘In January [2001] we had 85000 birds,’ he said. The waders
do best during droughts, he thinks, when the ponds grow shallower because toilets are flushed less often to save water.
Werribee is always busy. Ducks, swans, coots, moorhens and grebes crowd the waters; the reedbeds shelter crakes, rails and reed-warblers; the paddocks feed ibises and (endangered) orange-bellied parrots; and the skies teem with swallows (looking like cinders rising off a fire). Melbourne’s lavatory movements sustain all the creepy-crawlies and scum that feed these birds. Reptiles thrive here too. Tiger snakes devour the bell-frogs that fatten onthe bugs living in the weeds along the 66 kilometres of drains – which means that deadly snakes also benefit when Melburnians flush their loos.
Treated water finally feeds into Port Phillip Bay through four outfall pipes. Biologists looking around them have found a rich benthos (sea floor population), with crowds of scavengers and deposit feeders. The polychaete worm (Ceratonereis erythraeensis), which reaches densities of 14000 per square metre, is a key food of stints and sandpipers. The intertidal reefs are crowded with turfs of fertiliser-fed seaweeds (Gelidium pusillum, Ulva rigida, Corallina officinalis). When rotting seaweeds pile up on Melbourne beaches, nutrient enrichment (from sewage pollution) is sometimes blamed. Sea lettuces (Ulva), which are also thriving on rocks around Bondi Beach, are good markers of pollution. They are good eating if you are truly committed to recycling. They attract little crustaceans – amphipods and copepods – that graze on diatoms living on the ‘leaves’ and become food for fish, feeding nutrients back up the food chain.