SilvereyeAustralia’s beloved native birds are unwittingly playing a lead role in the destruction of their own landscape – by helping to spread the green plague of invasive plants introduced by people.
But, after studying the problem closely, researchers in the CRC for Australian Weed Management Dr Carl Gosper and Dr Gabrielle Vivian-Smith, believe it is possible to help birds do the right thing – and assist in restoring native vegetation.
“Birds are one of the most important factors in the spread of weeds throughout Australia. They eat the fleshy fruits of invasive plants, then fly away and defecate the seeds in another area. The seeds then germinate to give rise to new infestations,” explains Dr Gosper.
“Birds reach places that humans can’t easily get to, which leads to weed outbreaks in national parks, reserves and other wild areas. This poses a major challenge for weed managers.
Among the weeds of national concern threatening large tracts of the continent which are spread by birds are lantana, blackberry, bitou bush, camphor laurel, pond apple and bridal creeper. Birds which play a role in their spread include silvereyes, currawongs, honeyeaters, figbirds, bowerbirds and fruit pigeons.
Birds are attracted by brightly-coloured fruits of the right size, rich in sugars or other nutrients and available at the right time of year. Unfortunately, says Dr Gosper, some of these features also appeal to gardeners – with the result that gardens and birds combine to cause weed infestations elsewhere.
To work out exactly what is on the menu of native birds, the researchers enlisted the support of ornithologists and bird-lovers to report back what they observed them eating. “In SE Queensland, for example, native birds were seen feeding on weeds such as lantana, broadleaf pepper and Chinese elm. As a rule, the smaller the fruit of the invasive plant, the greater the number of bird species able to spread it.”
One reason birds turn to introduced plants is because land clearing and urbanization have removed the native fruits that originally sustained them. When planning revegetation of native bush or even urban tree-planting and gardening, it is important to make sure species are also carefully chosen for the appeal of their fruit to native birds. “Then, at least they’ll be spreading local native plants and not invaders,” he says.
Study of figbirds in the Brisbane area gave Carl another idea: the birds’ preference for roosting in one spot could be exploited by creating artificial roosts which in turn would become places where weed seeds in their droppings concentrate – and can be controlled.
“We also need to make gardeners more aware what plants not to grow in their gardens – because they have a high risk of being spread by birds.” This includes plants like mock orange (Murraya) in the subtropics or cotoneasters in cooler areas. Gardeners also need better information about what native plants they can grow in their gardens which are attractive to birds – and which will benefit, instead of imperil, the wider native landscape. Pruning of shrubs after seed-set and biological control with insects that damage the fruits before they can ripen are other options. Dr Gosper adds that the study of native bird feeding and movement habits may also have benefits at the landscape scale, in helping managers to anticipate and control future unwanted plant invasions.
More information:
Dr Carl Gosper, Weeds CRC and Qld Dept of Natural Resources & Mines
Phone: 07 3375 0751 or 0408 424 559
Dr Gabrielle Vivian-Smith, Weeds CRC and Qld Dept of Natural Resources & Mines
Phone: 07 3375 0737 or 0410 881 303
Peter Martin, Weeds CRC
Phone: 08 8303 6693 or 0429 830 366

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