The New Nature Page 12
What all these stories show is that no law of nature forces native animals to prefer their natural foods, or even to recognise them. Some do (say koalas on gum leaves), but many don’t. A currawong guzzling grapes might not look quite natural to us, but the bird doesn’t see it that way. By nature it is an opportunist. For our native wildlife, the foreign plants and animals flourishing in Australia today afford untold opportunities too good to pass by.
1 When rainforest is cleared it’s the first plant to clothe the bare earth, before the rainforest returns.
‘Can we acknowledge our universal presence and factor it into our study . . .?’
David Ludwig, Ecological Society of America, 1989
Most animals and plants now live in humanised landscapes. Their lives are touched by ours, either directly or by changes we make to the landscape, including the foreign species we introduce. Nature and people might be thought of as separate entities, but they don’t reside in separate places. Where people are, nature is too.
But many biologists don’t think like this. ‘I was a student when ecology was up and coming,’ Carla Catterall of Griffith University told me, ‘and I was taught that ecology is the study of natural processes. If you were going to do an ecological study it had to be in a natural site far away from human influences. Otherwise your work could be criticised as not really being a study of natural processes. There is much greater appreciation today of the fact that ecological processes go on whether or not humans are part of the system.’
In England, where animals have no choice but to live among people, ecologists happily study beetles on demolition sites and newts in quarries. They put out books such as The Ecology of Refuse Tips and write earnestly about topics like the ‘canine zone’, the epiphytic community of algae, mosses and lichens that colours trees where dogs cock their legs. (Absorbent bark attracts the most moss.) Australian biologists could follow their example and pay more heed to the habitats we engineer.
The habitat that most interests me, because I live in one, is the city. Cities are extraordinary places. They are far more significant, ecologically, than most of us think – as the exploration of sewage in chapter 5 shows. Designed to feed a large number of resources to a large number of people, they offer excellent opportunities for certain animals and plants. Urban resources are abundant and reliable, an important consideration in a drought-prone land.
Cities harbour surprises. There are platypuses in Melbourne (Merri Merri Creek), Sydney (national parks), Brisbane (Jindalee, Kenmore) and Hobart (found 1.3 kilometres from the GPO). In Cairns thirty to fifty crocodiles up to 4 metres long lurk in Trinity Inlet. One was run over recently by a taxi driver who thought it was a speed bump. Tasmanian devils sniff about the fringes of Hobart at night. Penguins live at St Kilda, close to Melbourne’s centre, and there are tiger snakes along the Yarra. Two-metre whaler sharks live in a golf-course lake beside Brisbane at Carbrook. Marbled geckoes (Christinus marmoratus) live among tombs in the Melbourne General Cemetery, and sand goannas (Varanus gouldii) live in Perth’s Karrakatta Cemetery, emerging from burrows among graves to bask on the darker headstones, which heat up faster. More than half of Australia’s bird species are found in the Sydney region, and more than seventy visit the grounds of Melbourne’s zoo, 3.5 kilometres from the city centre, including eight birds of prey. Foreign cities harbour many surprises, including India’s urban monkeys and peacocks. A decade ago I was in Bombay when a leopard attacked a man on the city outskirts. (He escaped, but lost his jaw.)
Of the many ways in which animals and plants take advantage of us, some associations form by choice, some date back a long time, and none should be viewed as unnatural. But how do all these interactions work within a whole habitat – in a city, for example? And what are the ecological principles that underlie what we see?
Mosquitoes are probably our most-studied urban animals, for the worrying reason that Ross River fever – a mosquito-borne marsupial disease – is burgeoning in our cities. My Brisbane suburb is home to five or more different mosquitoes, including the pollution-tolerant brown house mosquito (Culex quinquefasciatus) which likes drains and sewage farms. Each species behaves differently. Brown house mosquitoes whine into my bedroom at night, while Aedes notoscriptus, the ‘domestic container mosquito’, is silent, stays outside and bites before dark. A. notoscriptus, a pretty little insect with white-banded legs and a white-spotted body, is the ultimate urbanite. It breeds in backyard gutters, birdbaths, barrels, tins, tyres and tanks. Its wrigglers (larvae) do well even in water-filled saucers under pot plants, in leaf axils of bromeliad pot plants, and in stubbies lying by barbies. They have been found breeding in vast numbers in flower vases at cemeteries. As protection against fish and other enemies the eggs are laid above ground level, in shady or semi-shady spots.
These mosquitoes would have been rainforest insects in the past, breeding after rain in tree holes, leaf axils and fallen palm fronds. They still use cavities in figs and other rainforest trees growing in parks. (Eucalypt trunks don’t offer water-holding hollows.) These days they can breed whenever the patio plants get water, right through the longest droughts. They are thriving in their urban homes. Some other mosquito species breed on the marshy margins of cities and then buzz in to feed, but A. notoscriptus doesn’t need to. One study found a maximum distance travelled during life of only 238 metres. That study, published internationally in the Journal of Medical Entomology, especially interests me because it was conducted in my street, by a scientist living down the road. Luckily I wasn’t bitten by any of his 3000 pink- or blue-dyed mosquitoes.
Flying-foxes in cities have also become objects of study. When Francis Ratcliffe studied them as orchard pests in the 1930s, most camps were hidden away in ‘unfrequented and often inaccessible spots’, mostly within rainforests and mangroves. But, as we saw before, most bats now sleep in town, in gullies backed by housing. Brisbane’s many camps today compare with none in Ratcliffe’s day. Bats have gone urban because forests have shrunk (especially productive forests on fertile soils) and because city trees are productive and reliable. Nicki Markus radio-tracked several of Brisbane’s black flying-foxes and found remarkable fidelity to preferred suburbs. Bats were commuting night after night to the same streets, sometimes to the same trees, returning month after month until her study ended. They knew Brisbane like any good taxi driver. They were especially targeting exotic fruits from weeping figs (Ficus benjamina), queen palms (Syagrus romanzoffianum) and Chinese elms (Celtis sinensis), and also the nectar of a north Queensland eucalypt, cadagi (Corymbia torelliana). Urban trees which are fed extra water and fertiliser often fruit and flower very generously. Bats in Brisbane’s innermost colony (Norman Creek) need to travel smaller distances to food (2.9 kilometres on average) than bats further out (averaging 7.5 kilometres), thanks to enormous figs in old parks – the same figs mosquitoes breed in. Nicki found that ‘a more sedentary lifestyle in an urban environment is fostered by the reliability of resources’. Ratcliffe insisted bats would ‘on no occasion’ roost in eucalypt forest, but today they dangle from gums and she-oaks.
To the south of Brisbane, bats have formed camps in many towns as well as in four capital cities: Sydney, Melbourne, Adelaide and Canberra. Melbourne’s grey-headed flying-foxes feed entirely in parks and gardens, on Moreton Bay figs, eucalypt blossom, stonefruit and Mediterranean figs. In winter a majority migrate north, the remainder relying on the copious nectar flows of spotted gums (Corymbia maculata) from New South Wales and Queensland growing in parks. Melbourne’s colony is the most southerly on earth, the bats that remain in winter probably relying on the warmth of the city. (In Europe and North America urban heat benefits many birds and plants.) Bats have changed their diet, roosts, distribution and migration to fit in with us. The grey-headed flying-fox is now becoming a human commensal, ecologically tied to Homo sapiens.
The powerful owl, our heftiest night bird, a huge raptor with gleaming yellow eyes, is another animal mocking the experts by takin
g up city life. Naturalist David Fleay in 1968 described it as ‘highly nervous, exceptionally shy and wary’, and belonging to ‘the dense gullies of a timbered mountain habitat’. He’d be gobsmacked to know that today there are powerful owls in the middle of our two biggest cities. They perch over busy paths and cough up pellets of possum fur and bones. One of these owls first appeared in Melbourne’s Royal Botanic Gardens many years ago; the first sighting in Sydney’s gardens occurred in 2000. Scientists claim that powerful owls need vast territories of intact forest 300 to 1500 hectares in size. In Victoria they’re listed as an endangered species and in Queensland they’re rated vulnerable. They haven’t moved into Brisbane’s city gardens (yet), but they do use bushland reserves bounded by suburbia. Numbers in Brisbane are the highest they’ve been for a hundred years, thanks probably to urban possums and bats. Sydney’s owls are known to take cats. Owls in forests do need vast territories, because food there isn’t as plentiful. Gardens and parks carry more meat on the branch per hectare, obviating the need to roam widely. The problem for urban owls is finding tree holes for nesting.
Cities are reliable. Mosquitoes, bats and owls usually get what they need – water, blood, nectar, fruit, meat. Supplies aren’t limited by drought or bushfires, a big plus in so unreliable a land. Cities are places of plenty for those who fit in. The owl isn’t the best example of this, having a tiny urban base and relying mainly on forests to survive, but plenty of birds do excel in cities. Canberra’s birdwatchers learned this when they conducted a detailed survey of the ACT. Canberra, whose name means ‘meeting place’, is well-named from a bird point of view. Birds preferring the city over the country include all the waterbirds I mentioned before that use artificial lakes and dams.2 There are also fruit- and insect-eaters that go urban in winter, when natural foods grow scarce. Silvereyes roam all over the ACT in summer, but by July the only birds left are the flocks inside Canberra, some a hundred strong. Fuscous honeyeaters, also found in huge winter flocks in Canberra, weren’t recorded in the ACT at all until 1963. Black-faced cuckoo-shrikes and king parrots also go urban in winter. Swallows, kestrels, and crested pigeons (their numbers multiplying dramatically in recent times) do best in the paddocks bounding the capital. Canberra, with its milder climate, lush gardens and forested hills, is now regionally important for birds. It evidently sustains some of the honeyeaters that flock into Namadgi National Park, further south, in summer. The national park is now bound ecologically to the city.
Well to the north, biologists Sven Sewell and Carla Catterall have found remarkable densities of birds in Brisbane gardens. ‘The planted suburbs and canopy suburbs in summer were characterised by a bird species richness far higher than in any other habitat, including native forest, and in winter comparable to native forest.’ Well-treed cities guarantee more fruit and nectar, and probably provide more insects (feeding on well-watered garden plants in enriched soil). When eucalypts are retained on housing estates they end up flowering more prolifically than trees inside forests, thanks to higher light levels and probably to extra water and nutrients in gardens. Sven and Carla recorded eucalypts in bloom at two-thirds of their urban sites (within the ‘canopy suburbs’ where eucalypts were retained), but only at 10 to 20 per cent of forest sites. Many gardens also had flowering grevilleas (bred to flower profusely and continuously), which don’t occur at all in local forests. All over the world, when transects are run from cities out to forests, the highest bird tallies often come not from forests but from bushy outer suburbs or variegated farmland. In Britain, notes urban ecologist O.L. Gilbert, ‘suburban gardens are believed to support the highest density of breeding birds of any habitat’. The blackbird population in Oxford reaches twenty times the density of woodland blackbirds. Garden birds, says Gilbert, are ‘mostly woodland birds which find the mosaic of habitats resemble the richest of wood margin ecotones’. That may be true here too.
Cities obviously carry very high densities of certain animals: possums, seagulls, lorikeets, butterflies, green ants; the list goes on. I do fauna surveys in forests near cities (as an environmental consultant) and am often astounded by what I don’t find. You’d be amazed how hard it can be to find a ringtail possum, magpie, peewee or fence skink in intact forest. In England hedgehogs, foxes and frogs all reach peak densities in suburbs, and in America the same holds true for raccoons, coyotes and opossums. White-tailed deer reach densities of twenty-six per square kilometre in metropolitan Chicago, compared to only ten in forests. The first striped skunk I ever saw was hiding under a car.
One morning I conducted a little experiment in my garden. I wandered about for five minutes and counted fourteen grass skinks (Lampropholis delicata). Then I drove a kilometre along my suburban ridgeline to the last remaining fragment of forest, a little square that matches mine in aspect and elevation, fated soon to drown under housing. I looked for twenty-seven minutes before I could find a lizard. It belonged to a species never found in gardens. Later I saw a whip snake and some fence skinks, but failed during my hour-long search to find any grass skinks. They weren’t there. Returning to my car, I spotted one in a garden over the road. Here is more evidence that urban ecosystems exist. Grass skinks weren’t on my ridge when it carried forest; they avoid dry slopes. Messy gardens, busy with insects, suit them better than anything nature offers. They will move into that last wild place when the houses go up and the gardens go in. And they will lure in predatory white-crowned snakes (Cacophis harriettae), which also like gardens best. I caught one outside my house that was longer than the maximum recorded in books. That ridge site will end up with far more reptiles than before, but – an important point – it will not have as many species.
This is a common scenario: an artificial environment supporting more animals than a forest, but with fewer species overall. It’s a reason for feeling not so pleased about all the wildlife in our cities. Winners prosper and losers disappear. Fruit-flies in southern Queensland match this pattern. Rainforests contain the most species, but gardens carry more flies overall because Queensland fruit flies (Bactrocera tryoni and B. neohumeralis) do extremely well on backyard fruit. Their preferred breeding habitat, says S. Raghu, is now suburbia, because garden fruits are much bigger and more bountiful than rainforest berries. Crops and plantations offer similar advantages to other insects (and birds).
Cities end up with more species than they might because they are structurally diverse. Viewed from on high there’s much more than just buildings and roads. Run a transect from the concrete soul of a city to its leafy fringes and you cross a kaleidoscope of habitats – housing, parkland, waterways, wastelands, weed thickets, golf courses, bridges, remnant forest, reservoirs, more housing, quarries, dams, paddocks, orchards, rural estates, market farms, sewage farms – each with its own guild of species. Banded lapwings, for example, are aerodrome specialists. Forests, by comparison, vary less. But cities also outdo forests on a smaller scale. A rambling garden may feature rock walls, lawns, shrubbery, compost heap, timber pile, fish pond, birdbath, trees, house, garage and garden gnome. And they are often floristically more diverse than an equal area of forest, when every weed and garden plant is taken into account. Because of this diversity cities end up accommodating species from many sources. There are cliff-dwelling peregrines, seashore seagulls, swamp frogs, rainforest insects, woodland birds and cave moths, all coming together in new combinations.
Native plants don’t do well in cities, although there are exceptions. Mangroves are expanding in Sydney and Brisbane in response to siltation and pollution. Brisbane’s most intractable lawn weed is pitted blue grass (Bothriochloa decipiens), a native plant. It dominates my footpath, while native swamp dock (Rumex brownii) and wandering jew (Commelina diffusa) do well out the back. Many tiny native plants grow unheeded in our cities on eroding footpaths and in pavement cracks.
But cities are hostile to most wildlife, of course. The percentage of species that can use them remains relatively small. Freshwater fish, for example, do very poorly. Melbour
ne’s Royal Botanic Gardens has a lake full of plump eels, but I can’t offer many examples like that. However, I would make the point that our cities seem to be gaining more species than they are losing, at least among birds. This trend is very noticeable in England, where kestrels, bullfinches, siskins and magpies are multiplying. Every birdwatcher in Australia can think of birds that weren’t around fifteen years ago. More than fifty new species have been recorded in Sydney since 1958 – although most are vagrants, just dropping in occasionally, or seabirds. Birds on the rise in Sydney include brush-turkeys, koels, channel-billed cuckoos, satin bowerbirds and powerful owls. Koels, which are cuckoos, exploit the red wattlebird, which has increased with the planting of bottlebrushes. More flowers means more cuckoos. Birds are responding to the greening of cities and kinder values. In the past, animals on city fringes were ruthlessly shot. ‘An inborn, insatiable desire to kill something is one of the worst traits of Australian youths,’ wrote Frank Littler in 1902. ‘They appear to feel that it is dependant on them to “slay, and slay, and slay.”’ As late as 1958 a Sydney bird-lover could complain that the ‘continuous discharge of guns is becoming an all-too-common sound’.
One of Brisbane’s newer birds is the white-headed pigeon, found eating camphor laurel berries in parks. I used to wonder if these handsome birds nested within the city (with so many aggressive birds about), or retreated to nearby rainforests to breed. Early in 1997 I found out. I returned from abroad to find a pair in my garden. Their nest was concealed in thick jasmine high in a tree. I tailored my day to fit theirs, starting with late breakfast on the verandah and finishing each day out there with a beer. The male sat on the nest by day, the female taking over between four-thirty and five-thirty each afternoon. The male returned each morning. Later I saw the fledgling emerge and the father feed her. I watched the parents mate. The female squatted low on a limb while the male trod back and forth on her back before mounting from behind. Butcherbirds sometimes harried these gentle birds but never discovered the hidden nest. I read up on white-headed pigeons and was shocked to find that no-one had recorded their breeding rites before. I was the first to see them mating, and to learn that males sit by day and females at night. You read it here first. It’s an interesting example that shows the ecological relevance of the city. I recorded the secret lives of rainforest birds from my verandah over soggy cereal. I don’t live on acreage near bushland either: there are hundreds of houses around. Cities deserve to be taken seriously as habitats.