H5N1 Bird Flu Threatens to Unravel Australia's Ecosystems, Not Just Its Birds

The lethal H5N1 strain of bird flu, which arrived on the Australian mainland in June, is raising concern not only for the roughly 850 bird species found in the country — nearly half of them found nowhere else — but for the wider ecosystems those birds sustain. Australian authorities estimate about 30% of the country's bird species are at high to extreme risk from the virus, with five species at extreme risk of being unable to survive an outbreak.

Birds carry out ecological roles that are otherwise left unfilled in Australia, researchers note. Mound-building birds such as orange-footed scrubfowl and Australian brush-turkeys turn over large volumes of soil and leaf litter, aerating it and helping seeds germinate. Waterbirds such as black swans and whistling ducks disperse seeds and help balance plant growth in wetlands, while foraging herons and ducks stir up mud that boosts oxygen levels and circulates nutrients. Seabird colonies deposit nitrogen and phosphorus-rich guano that supports fish hatchlings and other species.

Overseas, H5N1 has already caused severe losses: the virus killed millions of black-headed gulls, and a population of coastal peregrine falcons in the United States fell by more than half after the virus arrived. In Australia, the main casualties so far have been petrels and crested terns, and it remains too early to predict the wider ecological impact.

Honeyeaters, which pollinate many Australian native plants that co-evolved with them, are among the species that could be affected; a sharp drop in their numbers would force greater reliance on wind or short-range pollination by less mobile species, which the researchers note leads to inbreeding and reduced fruit and seed production in affected plants. Scavengers and predators are also vulnerable to infection, undercutting their usual role in limiting disease spread.