The New Nature Page 21
‘Native gardening’ might have helped the environment had it usurped other forms of gardening. What it did instead was bring more plants onto the market – without taking any away. The pool of invasive species grew. Fortunately problems usually ensue only where gardens adjoin bushland. In those settings we really need gardens full of non-invasive plants. It matters less where they come from. In Feral Future I say that ‘benign azaleas and roses are better than weedy wattles’. A true native garden should carry only local native – indigenous – plants, produced from local seed. It’s a worthy goal for those with the time to try it. Gardens of Australian plants should really be called national gardens. They often look delightful, but we should not imbue them with virtues they don’t possess.
The last six chapters have looked at changing distributions from four angles. There are self-spread immigrants, hitchhikers, releases and escapees. What emerges is a complicated picture of change. The new populations don’t fit neatly into our preconceived notions of native and exotic. How should we define them? Where an insurmountable barrier has been crossed – a desert or a sea – ‘exotic’ is usually the right word. Lord Howe Island now has exotic lizards, frogs, insects, spiders and plants. Some of these newcomers threaten rare island species, and Australia has failed in its obligations to this World Heritage site by not keeping them out. The lizards (Lampropholis delicata) in particular could destroy unique insects if they reach the densities achieved in my garden. As Laurence Mound complains, ‘in terms of trading patterns, the Island is effectively an eastern suburb of Sydney and the resultant absence of quarantine restrictions sits uncomfortably with its World Heritage status’. Proper quarantine isn’t applied because the island is not considered foreign, although foreign it is. Western Australia’s approach is more sensible. Quarantine checkpoints at Eucla and Kununura keep out organisms from interstate.
But what if the distance moved is small? Macaranga trees (Macaranga tanarius) in Brisbane are busily escaping from gardens; I’ve seen a seedling in a railway cutting, another in an inner-city carpark. With their saucer-sized leaves they dramatically change any forests they invade. Macaranga is native to Brisbane, but only just. It grows naturally on a long ridge that winds down from the west. The escapees I see in local rainforests haven’t spread very far and I baulk at calling them exotic. They probably grew here in the past during wetter climatic times. If so, they don’t fit the World Conservation Union’s definition of alien invader, which excludes reintroductions. Nevertheless I abhor their use in local revegetation projects, which seems careless and unnecessary. But we can keep them out of local forests without labelling them as exotic.
The same goes for tuckeroo (Cupaniopsis anacardioides) around Sydney. Debate rages about whether Sydney’s oldest tuckeroo trees are natural or planted, even though the species clearly belongs in coastal rainforests further north and south. Nowadays it is spreading from gardens into completely new habitats. The koalas around Adelaide also fail the World Conservation Union’s ‘exotic’ test. Fossils imply they were widespread in South Australia when the climate was kinder. Lyrebirds in Tasmania, pittosporum in central Victoria, and flame trees in Sydney may also be reclaiming lost ground. I hesitate to call Tasmania’s lyrebirds exotic invaders, but I accept they do great harm. The galahs and crested pigeons that invade new regions also fall into some undefined category between native and exotic.
I also wonder about all the southward movements. Global warming (natural, as well as pollution-induced) is surely aiding the advance of umbrella trees, palmdarts and pittosporum. It’s a rule of conservation thinking that we let animals and plants migrate with climate change, as they did in the past. If umbrella trees were already coming south, does it matter if we help them along? There’s an interesting conceptual issue to resolve here, but fortunately the courses of action often remain clear. Umbrella trees and pittosporum (and to a lesser extent macaranga and tuckeroo) need controlling because they are highly invasive, replacing diverse systems with monocultures. Koalas in South Australia need curbing because they kill trees. Nature seldom produces monocultures – or dead forests. Our committment to biodiversity should guide us even when doubts arise about processes and definitions.
‘What’s the matter with all the birds?’
Jessica Tandy in Alfred Hitchcock’s The Birds (1963)
Kangaroo Island is home to a clan of endangered glossy black-cockatoos living far removed from the rest of their kind in eastern Australia.1 When Stephen Garnett wrote of their plight some years ago he suggested that fires (scorching their foodplants) and honeybees (stealing their nest holes) were the main threats to their future. But after studying the birds first hand, he decided differently. The main problems they face are possums, corellas and galahs. Honeybees come fourth.
The island has become a patchwork quilt of paddocks and forest that is ideal for brushtail possums. They graze the fertilised sheep pastures by night and doze the days away in nearby tree holes. But cockatoos need tree holes too, for nesting. When Stephen’s team monitored ‘glossies’ at the nest, eggs and chicks kept disappearing – and possum hairs left behind were the only clues. A remote camera filmed a possum evicting an adult bird. The verdict was clear. Possums were gobbling down cockatoo eggs and young and commandeering their tree holes. Brushtails taken to New Zealand long ago (an unmitigated disaster) are known to devour the eggs and chicks of rare birds, but no-one anticipated the same crime here. Our mammal books fail to even mention eggs and chicks as items on the possums’ menu. Possums are portrayed as vegetarians when really they fancy a little flesh. On Kangaroo Island they avoid the large tracts of forest that cockatoos originally used, and before clearing the two would rarely have met.
Following Stephen’s findings, possum-proof metal sheets were nailed around nest trees and cockatoo breeding improved. Sixteen young fledged in 1996, compared with five the year before. In 1997, in a roadside strip of forest, Lyn Pedler showed me three of the collared trees he guards. A cockatoo chick lay snuggled in one as we spoke. The possum problem had abated, he said – over a hundred trees have been collared – but a new peril had emerged. Galahs and little corellas were going down holes and killing cockatoo eggs and chicks. Lyn put Blu-Tack eggs in one hole and found them discarded a week later, disfigured by galah claws. Galahs and corellas are Outback birds that colonised Kangaroo Island after farmers cleared the land, galahs in 1913 and corellas in 1969. Lyn spoke of corella flocks 400 strong. Now they are culled to give ‘glossies’ a better chance.
Here’s another story that illustrates one of my themes. When something’s in trouble we need to be open about the reasons. They may include a native animal or two, something cute or colourful. Biologists are coming up against more and more examples of birds and marsupials causing eco-strife. Australia’s native animals are emerging as a significant threatening process. The mammals I’ll return to later, it’s birds that concern me here.
In 2000 the federal government brought out its Action Plan for Australian Birds. In this monumental work, 4 centimetres thick, Stephen Garnett and Gabriel Crowley plead the plight of all our rare and seriously declining birds. What astounds me about this tome are all the native birds mentioned as ‘threats’ to other birds. I counted nineteen. Some are only possibilities, like the kookaburras that may be stealing nest holes from Tasmania’s dwindling masked owls, but most are very real. At risk are twelve nationally endangered birds (see Appendix II), with other species in lesser strife. Yet only one of Australia’s twenty-seven exotic birds counts as a threat: the starling. Other recent reports blame birds for killing eucalypts, grasstrees and endangered plants. Then there is Zöe Tanner’s thesis (see chapter 13) on rock-rolling lyrebirds, and all the evidence linking birds to weeds. Australia is mired in native bird problems, all linked to us and especially to the clearing we do. And I’m only talking about conservation here, not conflicts on farms.
Here’s a funny story. At Cottles Bridge, Victoria, where Clifton Pugh once lived, there’s an artistic co
mmunity. The locals were feeding white-winged choughs – canny, crow-like birds with sickle-bills and weird voices – and their numbers rose. These well-fed birds nearly wiped out an extremely rare orchid, because when they weren’t begging for bread they were snacking on orchid tubers. ‘I’ve known that place for twenty-five years and it was one of the most orchid-rich sites I’ve ever known,’ explained Geoff Carr, who found and named the rosella orchid (Caladenia rosella). ‘The choughs have just about destroyed the lot.’ His new species, ‘a gorgeous plant with a candy pink flower’, was saved by local botanist Cam Beardsall. Cam bought land to conserve the orchids but watched their numbers dwindle. He couldn’t understand why one population dropped from a hundred to just ten or fifteen. Then he saw a chough dig up an orchid and the penny dropped. He raised cages over the surviving orchids and implored locals to stop feeding birds. Orchid numbers slowly rose. There are now seventy or a hundred plants. ‘That person single-handedly saved that species from extinction,’ Geoff told me. The rosella orchid does survive at other sites, but in miniscule numbers amounting to about twenty plants.
Cam says choughs and orchids both like treed hills, and people at Cottlesbridge do too. Each hilltop home boasted its own colony of choughs commuting between kitchen window and farm dam. ‘Choughs like the combination of open forest and clearings,’ Cam told me. Within the forest, havoc was under way. ‘It was like a chook pen,’ he said of one slope. ‘The choughs had just turned it over, destroying beautiful moss beds.’ Now that there are fewer choughs, magpies are occupying the hills and keeping them at bay. Closer to Melbourne choughs pose a hazard to another rare orchid, Caladenia amoena.
Venerable grasstrees (Xanthorrhoea) are dying in south-western Australia, and birds are again to blame. Ornithologist Harry Recher showed me old grasstree crowns in Dryandra Woodland stripped back by ringneck parrots sharpening their beaks. Old grasstrees on farms are dying because ringnecks are thriving within the agricultural landscape. They also deform blue gums in plantations by nipping shoots and stripping bark – a growing problem. The galah is another tree-killer. They chew away bands of bark around their nest holes in Western Australia, sometimes ringbarking trees. ‘In some areas in the wheatbelt, the galah is a significant cause of tree death,’ wrote Denis Saunders and John Ingram in 1995. The wheatbelt a century ago was a galah-free zone.
These are puzzling problems. No-one could have predicted that seagulls would attack stilts on Lake Eyre, or lyrebirds erode the Tasmanian wilderness. We can’t adopt a blinkered belief that birds live in harmony with nature. Nature keeps changing, and anything can happen. The range of birds posing problems is substantial. Currawongs, noisy miners and silver gulls head my list. Ravens and bell miners come next, but others are important too. My list would be very much longer if I counted in all the birds that bother people. Magpie-larks (peewees) are one example, implicated in bizarre attacks. Several were culled recently on the Cairns Esplanade for pecking at people’s eyes. A woman actually lost an eye many years ago, and only a few years ago magpie-larks were regularly attacking children at Atherton Primary School; their attacks started and stopped for no apparent reason. Stephen Garnett believes magpie-larks attack their own reflections in human eyes. (They also attack themselves in hub caps and windows, and other birds do this too.) Australian ravens also act unusually when they steal golf balls. ‘I laugh at it all the time, but its not a laughing matter on the golf courses’, said Sydney national parks officer Geoff Ross. ‘Ravens can steal quite a few thousand golf balls.’
Of all the problem birds, the pied currawong has attracted the most ire in modern times. Harry Recher wants them poisoned to avert disaster for other birds. These black, keen-eyed hunters have moved into gardens all over eastern Australia, where they attack birds and spread the seeds of weeds. In the past they were migrants, breeding in the ranges and descending to the coast for winter. The cold months were lean times, until currawongs found in gardens the winter-ripening berries of privets, hawthorn, cotoneaster and camphor laurel. These northern-hemisphere plants are timed to fruit in cold months when insects in northern lands are scarce. Sated by all the fruits, and discovering plenty of other food – pet food, garden insects, food scraps, and seed and meat left for birds – they stayed on in spring to breed, when small birds nest too. The chicks of these small garden birds became food for the currawongs’ untimely broods.
Currawongs were implicated by an elegant study conducted in 1993 by Richard Major and colleagues at the Australian Museum. On the TV show Burke’s Backyard homeowners were asked to place fake willie-wagtail nests (half a tennis ball baited with clay eggs) in their gardens. Nearly two-thirds of the 1803 nests were attacked, mainly by birds.2 Of the many attackers seen at work, half proved to be currawongs. Other egg-jabbers were magpies (13 per cent), noisy miners (10 per cent), wattlebirds (3 per cent), butcherbirds (2 per cent), and a few ravens, kookaburras, magpie-larks (peewees) and even silvereyes (1 per cent each). These were interesting findings in view of suggestions that numbers of small birds in cities are declining. Other birds, such as currawongs, may be eating their eggs.
Currawongs are bold. They will tackle full-sized turtledoves, tearing off their heads. They kill wattlebirds, blackbirds, sparrows and starlings. They stab swallows in flight. They supposedly kill young ringtail possums. They attack rats. They eat carrion. When Arthur White tried to rear endangered bell-frogs in a Sydney pond, a currawong ate one of the precious tadpoles. Currawongs are intelligent, alert and opportunistic, they know how to watch and await their chance. They will hide in shrubbery and strike from behind. They notice where nests are built.
Currawong victims are usually common birds. Many are exotic. Young starlings are pulled from eaves, and sparrows are torn from roosts at dusk. Currawongs may exercise good control over sparrows, whose numbers in Australia are falling. But one rare bird, Gould’s petrel, was facing doom from currawongs until national park rangers intervened. A pretty little seabird dressed in soft grey, the petrel comes to breed at only one place: Cabbage Tree Island, a few kilometres off Port Stephens in New South Wales. (Other subspecies breed in New Caledonia, Fiji and Vanuatu.) The petrels lay one egg on the ground below palm trees inside a rainforest. A thousand or so survived but numbers were dropping fast.
When biologists investigated, an odd story emerged. Rabbits brought over in 1906 for myxomatosis research were browsing back the undergrowth. Native bird-lime trees (Pisonia umbellifera) were dropping sticky pods onto petrel wings, immobilising and sometimes killing them. In the days before rabbits, the sticky fruits were intercepted by undergrowth. In 1992 the bird-lime trees were poisoned. A currawong was then seen dismembering a petrel. More than fifty stripped bodies were found. The currawongs were feeding rare petrel flesh to their young. Researchers David Priddel and Nicholas Carlile declared the carnage ‘severe and unsustainable’. Camphor laurels and lantana on the nearby mainland had drawn in the currawongs that now visited the island. Rabbits were exposing petrel nests to the prying yellow eyes of canny currawongs. When currawong nestlings were removed, the petrel’s fortunes rose. Australian ravens, another problem, were also controlled, and the rabbits were removed with diseases, poison and traps. With more shrubbery in place, petrel nests were harder for predators to find. This is a compelling example of cause and effect. Gardeners around Port Stephens, merely by growing berry-laden plants, were bringing doom to a bird that lives out at sea.
Currawongs also raid orchards and spread weeds. In early convict days they stole into fields and took new-sown grain. They are orchard pests today, attacking apples, stonefruits, tomatoes and strawberries. ‘They have exotic tastes,’ noted birder Bill Alison, ‘appreciating such culinary delights as Banana Passionfruit, Persimmon, Feijoa, Quince, Pumpkin, Mandarin, Pawpaw and Olives.’ Currawongs spread prickly pear seeds long ago and today they disgorge neat pellets of seeds at their communal roosts, which around Sydney contain any of thirty-six exotic plant species. One pellet contained 131 lantana seeds. David Bass colle
cted pellets at Armidale and counted out 34000 seeds, mostly from privet (Ligustrum lucidum) and firethorn (Pyracantha), major weeds. One of David’s proposals for weed control is to ‘intensively cull pied currawongs’.
But one bird, the channel-billed cuckoo, is doing well from all this. A big, hefty-beaked bird, it lays its eggs in currawong nests. Its chick evicts the currawong brood to become the sole object of parental attention. Cuckoo numbers are rising. These magnificent birds eat figs, and we could possibly help small birds by planting more figs in parks. (More figs should mean more cuckoos and thus fewer currawongs.) We should certainly strip our cities of all the berry-bearing plants that currawongs exploit. We ought to move fast, because currawongs numbers are exploding in Melbourne, Sydney, Brisbane and places in between. I seldom saw them around town fifteen years ago but now they breed next door.
Other aggressive birds to wonder about are butcherbirds, ravens, seagulls, miners, skuas, magpies and kookaburras. When Stephen Garnett assessed the plight of the endangered golden-shouldered parrot some years ago, illegal trapping and cats seemed likely threats. He now identifies butcherbirds as a menace. His reasoning goes like this: the parrots eat grass seeds on Cape York Peninsula. Paperbark tea-trees (Melaleuca viridiflora) are invading, helped along by cows grazing grass so low that bushfires no longer burn, and by graziers who quell fires. Aboriginal fires in the past stopped the paperbarks dominating by killing their seedlings. But now butcherbirds can skulk in paperbark thickets and ambush parrots.
‘We have video evidence that both pied and black-backed butcherbirds frequently visit the nest chambers of golden-shouldered parrots and peer inside,’ Stephen told me. ‘Also, during the wet season, pied butcherbirds frequently dive on golden-shouldered parrots. We have also found chicks with smashed skulls, apparently the typical killing technique of butcherbirds, and have found the remains of small chicks wedged in the tops of nests in typical butcherbird fashion.’ The parrots are now doing best in two regions where graziers burn as the Aborigines did.