Starvation diet

By Rachel Nowak in Melbourne THE deadly calicivirus that has devastated Australia’s rabbits may be having a knock-on effect on indigenous wildlife. Wedge-tailed eagles (Aquila audax) have not bred for the past three years in the Strzelecki Creek region of South Australia, according to a study from the Australasian Raptor Society and the state’s government. Rabbits had become the food of choice for many birds of prey, so the researchers suspect that the failures are due to food shortages. The calicivirus reached the mainland in 1995 from Wardang Island, off South Australia, where it was being tested as a method of controlling rabbit numbers. It spread quickly across the country, decimating rabbit populations. But from the start, conservationists have worried that either the virus itself, or the shortage of rabbits for food, would affect Australia’s natural fauna. Those fears now appear to be being realised—although to date there is no evidence that any species is seriously threatened. The overall abundance of birds of prey has declined in areas affected by the calicivirus, according to Birds Australia, an organisation that uses volunteers to estimate bird populations. Brown falcons (Falco berigora) are the hardest hit, with the number of sightings down by half over large swathes of temperate Australia. Curiously, the number of roadside sightings of wedge-tailed eagles has doubled during the summers since the introduction of the virus. But that may be due to changes in the birds’ behaviour bought about by hunger, claims William Steele, a project officer with Birds Australia in Melbourne. He suspects that the eagles are being driven to feed on road kills. Roger Pech, a population ecologist in Canberra with the Wildlife and Ecology division of CSIRO, Australia’s national research organisation, is sceptical of the Birds Australia data. For long-lived raptors it should be too early to see the effects of the reduction in rabbits, he says. But breeding success could be hit more quickly. CSIRO’s own studies of wedge-tails around Lake Burrendong in New South Wales have so far been inconclusive. In the first year following the virus outbreak, most of the eagles bred successfully. This year, however, breeding activity has fallen markedly. Another CSIRO study in the same region has found early indications that more brushtail possums, a native species, are being eaten by foxes and feral cats since the rabbit decline. “In the short term, it’s a real concern that feral cats and foxes will eat the indigenous species,” says Pech. But the reduction in rabbits may in the long term be beneficial to native animals. In the Journal of Applied Ecology (vol 35, p 434),
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