The New Nature Page 22
A butcherbird once launched an attack inside my house. Two crested pigeons were coming daily to my door to feed, and one day I placed the seed inside to test their mettle. As soon as they entered, a grey butcherbird fell upon them, driving one further inside. The pigeon struck the lounge-room window and slumped to the floor. I had to shoo the eagerly circling butcherbird outside. I opted against feeding birds after that. I’ve also seen butcherbirds terrorising finches in aviaries, impaling any birds panicked into perching by the wire. People who feed butcherbirds endanger the lives of other birds.
Magpies and kookaburras get fed too, and they too attack birds, although without threatening anything rare. Kookaburras were shot by early pioneers for stealing chickens from pens. They also raid nests. Magpies were often kept as pets (especially the musical Tasmanian birds) and their penchant for flesh was well known. A canary in a cage on the lawn would be struck through the bars. Magpies will even blind koalas that climb near their nests – the Brisbane Koala Hospital has several blind patients in permanent care.
Aggressive birds are a global concern. Seagulls, crows and ravens are multiplying on human wastes almost everywhere, and rare things are suffering. In Japan, for instance, seagulls are culled to aid threatened puffins. Alfred Hitchcock chose well to cast gulls and crows as his leading rogues. Apart from stilts, Australia’s silver gulls attack nesting fairy terns, little terns, tropic birds and hooded plovers – all scarce birds. On Barrier Reef islands they fatten on garbage from boats, tourist resorts and nearby towns. Michaelmas Cay’s black-naped terns failed to breed for six years running because gulls struck whenever tourists disturbed birds at their nests. It’s an international problem at seabird islands: the seagulls strike when tourists arrive. They follow people for the same reason cattle egrets follow cows – we flush prey. Gulls also eat baby green turtles and the eggs and chicks of noddies and terns. Seagulls and eco-tourism don’t belong together – check your favourite resort.
Ravens and skuas are also culpable killers. Australian ravens take muttonbirds, Gould’s petrels and Cape Barren geese eggs. They attack nesting hooded plovers and fairy terns and kill full-grown chooks in pens. At egret colonies they work in gangs, forcing young egrets to the ground to peck them dead and eat them. Forest ravens kill fairy penguins by taking out their eyes. Ravens, like gulls, are multiplying on human wastes. On Macquarie Island subantarctic skuas – dark, gull-like birds – go for rare blue petrels, white-headed petrels and fairy prions. They emerged as a problem when rabbits were freed on the island, rabbit kittens feeding a skua boom. The rabbits were removed and the problem abated.
Australia has two exceptionally aggressive birds – bellbirds (properly called bell miners) and noisy miners – that don’t prey on other birds. Their story is important, so I will tell it in full.
The tinkling of bellbirds is one of Australia’s prettier sounds. It moved Henry Kendall to verse: ‘Softer than slumber and sweeter than singing,/The notes of the bell-birds are running and ringing.’ Real estate agents swoon over the value bellbirds add to land. Homeowners will pay through the nose to live among tinkling bells. Sales agents joke about playing tape-recorded bell-miner calls. But bellbirds bring no sweetness to the forest. Other birds hear only bodings of terror. To the forest itself the tinklings toll sickness and death. Those sweet chimes belie savage habits. From colonies in eucalypt forests these greenish honeyeaters drive away other birds, even hefty ravens and kookaburras. Only small understorey birds are tolerated. The tinkling tells other birds to stay away.
Bellbirds are dietary specialists. They eat psyllids, tiny sap-sucking bugs found on gum leaves, and lerps, the sweet shields the bugs build. In colonies ranging from twenty to 200 they zealously guard their food-bearing trees. A colony may last forty years and command 2 hectares of forest. Because bellbirds harvest only part of their food supply, their eucalypts often suffer severe bug infestation. Bushmen will tell you bellbirds live in ‘sick’ forests.
Some years ago a Dandenong landholder illicitly shot the bellbirds on his land. Other birds came for the psyllids, and his trees improved. Word of his deed reached the ear of forestry biologist Richard Loyn, who in 1981 repeated the experiment, removing bell miners from a psyllid-sick forest near Melbourne. Even before the last of them were caught, thornbills, pardalotes and crimson rosellas rushed in to feast on lerp. The trees sprouted flushes of new leaves. The idea of honeyeaters helping to kill trees proved so bizarre that Loyn’s findings found a place in the international journal Science. Bell miners are, it seems, the world’s ultimate avian engineers.
‘Bell miners are true farmers,’ claimed Richard. ‘Their territoriality turns the trees into producers of bird food via psyllids, but at the forest’s expense.’ To allow them to control enough lerp, other birds must be kept away. Bellbirds aren’t discriminating enough to attack only lerp-eaters and nest-robbers, though, and many innocent birds such as bark-feeders are kept away. When their ‘farms’ sicken, bellbirds react in different ways. Some colonies let their trees die. More often they move, working slowly up a gully, or sliding boundaries back and forth, allowing trees to recover by leaving them unguarded for other birds to strip the bugs. Richard compared this to shifting agriculture, with trees left ‘fallow’.
Melbourne lies at the western edge of their range, and bellbirds here have gone urban. Their colonies often straddle gullies and run into nearby gardens, where nectar is taken from shrubs and water from birdbaths. Cats, dogs and people are sometimes mobbed. Garden trees are seldom killed, bellbirds defending them less diligently, perhaps because urban nectar is a reliable food. Bellbirds stole into the eastern suburbs in the 1920s, and although some colonies have fallen to development, others have ventured deeper into the metropolis. In the 1990s bellbirds claimed the Royal Botanic Gardens. One colony is centred on the gardens’ cafeteria, another on the planted eucalypts by the nearby Shrine of Remembrance. The gardens’ bird list – published in 1991 and sold in the shop – doesn’t mention bell miners. They keep heading west. In 2000 I saw the world’s most westerly bellbird, one that lives in a park in Geelong. Even before I locked my car I heard it ‘tink’. ‘You hear that?’ cried local naturalist Valda Dedman, my guide for the day. The bird had claimed thirteen small gums in a strip of park, a river rolling by on one side and factories on the other. Valda said it had turned up several months before and never left these trees. ‘I don’t know what’s brought it here.’ I paced out its domain. Thirty metres by nine.
Bell miners appear to be multiplying in eastern Victoria. They do well in farming belts where stressed trees attract lerps. By keeping birds away by day they probably benefit nocturnal lerp-eating animals. I spotlighted within a colony once and saw two sugar gliders and a tiny feathertail.
Bellbirds need water, which keeps them to wetter groves and gullies in south-eastern Australia. But they have a country cousin who is not so constrained. The noisy miner, also called micky miner and soldier bird (unrelated to the Indian myna, after which it takes its name), likes drier forests and enjoys broader tastes, eating many insects besides lerps and eagerly taking nectar. In woodlands and gardens across eastern Australia it has exploded in numbers and become a dominant bird. Noisy miners attack anything – koalas, cows, bats, dogs, foxes, horses, sheep, wallabies, snakes, pigs, goannas, people. A hundred may come to harass a goanna. I have seen them strike a blue-tongue lizard crossing a park. They vexed John Gould back in 1865: ‘when they follow you through the entire forest, leaping and flying from branch to branch, they become very troublesome and annoying’. They harry all birds, even ducks near water. They are the only creatures to lord over bell miners. Sometimes they kill. Two ‘mickys’ were seen to slaughter a sparrow by hammering its skull. Another gang pecked the eyes and crown of a pardalote until it fell down dead.
Colonies of up to several hundred occupy areas of up to 40 hectares. Both kinds of miner breed communally, multiple males attending each female and feeding her young. Female noisy miners are promiscuous, up
to twenty males visiting one nest, although most don’t mate. Males mob together when anything alarming appears. They have a complex vocabulary that includes different calls for different intruders. I am told when sparrowhawks pass my house by the high-pitched calls I hear. But noisy miners don’t oust all comers. Big birds – magpies, crows, butcherbirds, parrots and kookaburras – often defy their taunts and come to be tolerated. They make up the characteristic guild of birds found with miners. Butcherbirds and crows understand some miner-speak and join the attacks, striking at possums and owls, adding their caws to the cacophony. I once rescued a bewildered ringtail possum from a combined miner–butcherbird assault.
Noisy miners do best around clearings or where trees are well spaced. Stands of thinned eucalypts above a shrub-free understorey suit them perfectly, allowing them to harvest insects at all levels from the ground up. Thick undergrowth prevents them feeding down low and provides refuge for other birds. But where thick forests are penetrated by roads or settlements they line the edges. Almost everything we do aids this bird: partial clearing, logging, roads and tracks, removing understorey by grazing, mowing and fire. Other birds suffer both the injury of habitat loss and the insult of noisy miner attack.
Noisy miners have attracted many studies. Richard Loyn watched them invade one forest patch after cows were let in during drought. The trees then suffered ‘dieback and defoliation by insects’. Merilyn Grey removed miners from roadside remnants, and watched other birds flood in, including endangered regent honeyeaters. Carla Catterall evicted miners from part of Brisbane’s Toohey Forest close to Griffith University, and her findings proved equally dramatic. Her office looks out over trees where small honeyeaters once perched during winter. She planted a grevillea to feed them. ‘But then the carpark was extended and there was some further building around the university,’ she told me. ‘And then two large fires really opened up the understorey.’ Miners moved in and small birds stopped coming. Her grevillea now feeds noisy miners.
Carla has run transects though miner colonies, recording miners, miners and more miners, and transects outside, where different birds prevail. Boundaries are sharp. ‘There are places at the edge of miner colonies where there’s almost a tangible demarcation line,’ she told me. ‘Step a few paces one way and you’re in miner territory, with miner-type acoustics. A short walk the other way and there are the mixed flocks of fantails, whistlers, honeyeaters, etcetera.’ She took me to a thick gully from which she’d removed most of a colony. At the forest edge, beside houses, we heard a few miners as well as crows, lorikeets and turtledoves. We pushed through thick bracken, hovea and wattles. I would not have thought miners could deter understorey birds from using this. Moving on further we met up with a flock of small honeyeaters and pardalotes. They worked their way down the gully toward the remaining miners, then veered off to one side. Carla has found that when some miners are trapped, the others retreat toward the forest edge, close to roads and houses, and towards, she says, ‘the habitat that seems to suit them best’. They like edges: two habitats in one. Forest birds will reclaim vacated miner territory, but only after a couple of weeks have passed. They seem to learn where colony boundaries fall.
Miners are part of my life – they are calling outside my home right now. I keep an ear out for their cries because, like guard dogs, they herald visitors. Once they were calling so oddly that both my neighbour Jill and I went outside, where we found a skinny little green snake wending its way through a tree. Around Brisbane noisy miners reach peak densities in suburban gardens with a few remnant eucalypts. Next highest densities are found in gardens planted up with exotic shrubs and trees, then in small forest pockets, and then in forests stripped of their understorey. Very few miners occupy intact forest.
But what of the past? Two hundred years ago Brisbane was one large forest and noisy miners must have been scarce. They are dominant birds today, and are still spreading. They took over my mother’s place a few years ago. Now there are more spiders along her fence and no small birds to peck at them. Silvereyes, peewees, brown honeyeaters and sparrows have gone. My mother misses the willie wagtail that used to perch beside her when she gardened. Sparrows are vanishing from Brisbane, and miners can be thanked for that. ‘Sprags’ were the sound of my childhood but now I look with interest when I hear one. Graeme Chapman, in Common City Birds (1967), wrote that ‘Noisy Miners prefer open country with large eucalypts and so are not a garden bird in towns and cities’. They ‘have not adapted to densely built-up areas.’ That’s not true today – Sydney’s Hyde Park is full of them. They take crumbs from tables in some parks. They are turning into big native sparrows.
I asked Carla how noisy miners got by before Brisbane was built. How did they survive without roads and lawns and gardens? There was a long pause. Most forest around Brisbane is thick. Did they live here at all? We guess that some did, but only where Aboriginal fires kept the understorey free. John Oxley, surveying the river in 1823, saw some ‘open forest land’, including one stretch that was ‘very open and generally to be called quite level’ (at Bellbowrie). This sounds ideal. But the possibility remains that miners invaded after settlement from drier woodland nearby. That’s what happened in Hobart. In 1867 Morton Allport spoke to the Royal Society of Van Diemen’s Land about the sudden arrival of miners, magpies and eastern rosellas. ‘From the earliest days of Hobart Town, til a few years ago,’ he said, ‘these . . . birds were unknown, as residents, on the Hobart Town side of the Derwent, from Glenorchy to the Huon, although much of the country lying between these places is apparently similar to that inhabited by the same birds at a distance.’ Miners evidently came south from the drier Midlands as the country was opened up.
Miners did occupy Sydney in early times. Convict forger Thomas Watling painted one in 1790, beside which was written: ‘This chattering bird often gives notice to the Kangaroos when sportsmen are after them. It is pretty numerous, and always at war with others of the feathered tribe.’ It was probably a nuisance to Aboriginal hunters. Its stronghold was the shale country west of Sydney, as birder Keith Hindwood noted in 1944. It was rare in the sandstone then. Not today. Sheila Walkerton, now 69, grew up in Northwood, in sandstone country, on the same block of land she occupies today, and she remembers all the birds before the miners came. The bird diary she kept as a teenager from 1947 on shows that she first saw a miner in 1949, not in her garden but on a visit to Bankstown. I sat in Sheila’s lounge room, poring over her faded, nib-written notes, while miners called outside. They did not enter her valley until the early 1980s. She is losing more forest birds as time goes by. Since my visit a year and a half ago she’s lost silvereyes, spinebills and pardalotes.
Noisy miners are part of the much larger problem of forest clearing and fragmentation. Future land use will aid their spread at the expense of small forest birds, many of which are declining perilously. In Tasmania miners are thought to imperil the endangered forty-spotted pardalote, and on the mainland the endangered regent honeyeater. When small birds vanish from city precincts, cats usually cop the blame, but noisy miners are often responsible. How cats can kill birds living up in trees remains to be explained, but the means by which miners evict birds is well known. They may even alter forest composition by keeping out small fruit-eating birds that would otherwise drop seeds.
The bell miner also threatens an endangered bird, the helmeted honeyeater. Only about a hundred of these birds survive at one reserve at Yellingbo, near Melbourne. All their former haunts have been swamped by bellbirds. Their most recent demise was from Cardinia Creek in the Dandenongs where, biologists suggest, a dam and other disturbances stressed local trees, allowing psyllids and then bellbirds to invade. At Yellingbo bellbirds are culled to keep the honeyeaters alive.
Australia has two other miners, one of which is increasingly dominant. The yellow-throated miner looks and sounds like its noisy cousin but chooses drier country. It dominates many Outback towns. Where dams are dug for cows it multiplies in place of smaller bi
rds. It’s not particularly violent, but it does pose a threat to Australia’s fourth miner – a story told later.
Nectar is a resource worth defending, and nectar-feeding birds everywhere are aggressive – even tiny hummingbirds. Australia, dominated by eucalypts and other nectar-laden trees, supports more nectar-loving birds, and much bigger ones, than any other land. Our bird fauna is the most aggressive in the world. I see far more fighting here than when I birdwatch overseas. Noisy miners and bell miners are the most belligerent birds on earth, but other honeyeaters are feisty too. Red wattlebirds and New Holland honeyeaters are multiplying in suburbia, and other birds suffer from this. Whenever we plant nectar-rich shrubs we reward aggression. For this reason, some gardeners in New South Wales are now removing their hybrid grevilleas.
The noisy miner is unique, but over in the Americas there are birds that achieve the same ends – displacing other birds in fragmented forests – by very different tactics. The brown-headed cowbird is the chief culprit. Once upon a time it fed upon prairie seeds and snatched up insects stirred by the hoofs of bison and deer. Now it feeds around cows and loiters at grain depots. Numbers have exploded. Cowbirds, like cuckoos, are brood parasites. Females sneak their eggs into other birds’ nests to be hatched and reared in absentia. By skipping the work of rearing, they have energy to lay prolifically – sometimes more than twenty eggs a season. And unlike cuckoos, they lay indiscriminately, their eggs appearing in the nests of more than 220 bird species, 140 of which have reared brown-headed cowbirds. These parasites are multiplying faster than any other American bird and their hosts are declining. Two birds of the host species have been pushed to endangered status.