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Dieter Hochuli, a biologist at the University of Sydney.
    For the most part, plants and animals adapt to their urban surroundings using the traits that help them survive in their natural habitat. But some scientists predict there may come a point when the pressure of the city, especially from pollution, becomes so great that evolution will intervene.
    â€˜We’ve created this whole new habitat that never used to exist here,’ Angela Moles, a UNSW plant biologist, says. ‘There will be some species living here that are not doing so well and there will be selection for individuals who can do better in an urban environment.’
    If any species has learnt to thrive in an urban environment, it’s the native white ibis. Known as the ‘tip turkey’, the bird’s reputation for ferreting through inner-city bins and scavenging street garbage has not endeared it to the public.
    The white ibis began its move to the big smoke in the 1970s when large parts of its natural habitat, inland wetlands, became degraded or drought affected. ‘The species is a wetland forager,’says wildlife officer John Martin, from the Royal Botanic Gardens. ‘Now it forages in inland parks and landfill.’
    During the peak of their spring breeding season, more than 9000 of the birds call Sydney home.
    Specimens at the Australian Museum show the city’s bird life has changed dramatically over two centuries. Prior to urban development the native shrubs and bushland were populated by large numbers of small insect-eating birds such as the superb fairy-wren and the eastern yellow robin. Today, homeowners prefer to landscape their backyards with tall trees and manicured lawns, an environment that provides little protection for small avian species.
    But one bird’s trash is another’s treasure. Yards filled with flowering plants and fruit trees encourage omnivorous birds such as currawongs, bowerbirds and the city’s most despised resident – the noisy miner. ‘They’re a real winner in cities,’ Australian Museum ornithologist Richard Major says. ‘The predominant driver in the decline of small birds is that we’ve made a suitable environment for native noisy miners. They’re so aggressive they push out smaller birds.’
    But their disappearance has thrown a lifeline to the many insects that would have ended up as small bird tucker.
    Hochuli says many invertebrates such as the golden orb weaver spider and the blue triangle butterfly relish living in the city. The golden orb spiders in Sydney are fatter and more fit, he says. ‘We’re trying to tease out whether it’s more food or the urban heat island effect, as it’s up to 4° Celsius warmer in the city.’
    Hochuli has also found some varieties of ant more at home in the city. The green ant, known for its painful bite, will build a nest where there is space and food, regardless of whether it’s your backyard or a sports oval. ‘It’s remarkable how many things persist in urban environments,’ he says.
    But the decline in birds that eat small insects means thesepopulations grow unchecked, allowing them to chomp their way through the foliage of the city’s trees.
    â€˜Throughout the city we see these shifts in interactions between species as some jobs are lost,’ he says. And some shifts will be irreversible.
    â€˜We still have functioning ecosystems, they’re just different from what they were 200 years ago,’ Hochuli says.
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    While insects can survive in areas no bigger than a nature strip, mammals have been confined to patches of bushland scattered around Sydney and the national parks. But in the northern beaches, the rabbit-sized, long-nosed bandicoot has discovered the advantages of venturing out of Sydney Harbour National Park and into backyards.
    â€˜They forage for invertebrates in the grass and like the surrounding shrubs to nest and escape from