Yesterday, I woke to a cold, damp Canberra morning – and silence. The trees around my home were empty of feathered silhouettes. Even the usual bright-eyed, warble-voiced magpies were absent.
Author
- Penny Olsen
Honorary Professor in Ecology and Evolution, Australian National University
The next morning, they were back. I don’t know why they went AWOL. But their absence felt like a taste of what might come as the lethal H5N1 strain of bird flu spreads in Australia, affecting both birds and mammals.
Conservationists once asked : what is a bird without a tree to nest in?
This year, we may well wonder the grim inverse – what is a tree without a bird to nest in it? I can tell you. A tree without a bird is a miserable thing – and in a broader ecological sense, a tree without a bird could be in trouble.
In Australia, birds act in many roles that mammals or insects might fill elsewhere, from pollinating flowers to spreading seeds to keeping trees free of sap-sucking insects.
Bird flu doesn’t just threaten birds and mammals – it could well affect entire ecosystems.
Why birds matter so much
Australia’s birds play vital roles in most ecosystems.
As honeyeaters squabble in the canopy, mound-builders such as orange-footed scrubfowls and Australian brush-turkeys turn over vast volumes of soil and leaf litter on the forest floor, as they look for bugs or make their giant mounds.
Their digging loosens and aerates the soil, giving seeds a better chance of germinating and encouraging leaf litter to break down.
In more open woodlands and shrublands, this work is done by birds such as malleefowl, quail-thrushes and babblers.
In Australia’s wetlands, plant-eating waterbirds such as black swans and whistling ducks disperse seeds and help balance plant growth, while insect eaters such as musk ducks do the same for aquatic invertebrates. As foraging herons and pink-eared ducks stir up mud at the bottom to flush out insects, they boost oxygen levels and circulate nutrients.
As seabirds and shorebirds move between coral reefs, mudflats, islands and oceans, they deposit nutrients. Guano and other organic matter from raucous seabird colonies supply nitrogen and phosphorus for a host of species – not least fish hatchlings.
My favourite group are the falcons. These swift predators cull sick and weak prey, keeping the species fitter and helping keep the lid on pest species such as starlings, rodents and locusts.
What will happen if bird numbers plummet?
Bird flu is likely to hit some bird and mammal species very hard, but leave many others much less affected, if at all. Authorities estimate about 30% of Australian bird species are at high to extreme risk. Those at high risk face a “severe reduction” in population size, while the five species at extreme risk are potentially unable to survive.
Overseas, the virus killed millions of black-headed gulls, who live in big colonies. In the United States, a population of coastal peregrine falcons fell by more than half after the virus arrived. Waterbirds have been hard hit overseas.
The virus only arrived in Australia in June. To date, the main casualties on the mainland have been petrels and crested terns. It’s too early to predict what this might mean for Australian ecosystems.
If the virus led to insect-eating bird populations falling sharply, it could result in large trees dying. This is because eucalypts – particularly those already under stress – can gradually wither and die if birds don’t eat sap-sucking psyllids and leaf-eating weevils.
In Queensland’s tropical rainforests, cassowaries, pigeons and doves eat the fruit of trees and spread them in their fertilising dung. If these species were hard hit, the trees would be less widespread and fewer seeds would germinate.
In dry central Australia, emus, pigeons, parrots and finches play similar roles in spreading the seeds of grasses and shrubs. If their populations plummet, some plant species would gradually disappear from some areas and their genetic diversity would fall.
Uniquely in the world, a great many of Australia’s trees and shrubs have co-evolved with honeyeaters. Species such as the hummingbird-like eastern spinebill drink the nectar and act as pollinators .
If the numbers of sugar-seeking birds such as honeyeaters and lorikeets drop sharply, it would mean less cross-pollination. The plants are then forced to rely on pollination by wind or less mobile mammals and insects over much shorter distances, which results in inbreeding and a drastic drop in fruit and seed production.
It’s often claimed scavengers help stop the spread of disease. Unfortunately, bird flu can infect scavengers and predators.
What future for the land of birds?
Around 850 species of birds are found in Australia – and close to half are found nowhere else.
Birds play vital roles, from waste disposers to seed dispersers to pollinators and pruners. Birds control pests, produce fertiliser and engineer ecosystems through their digging. They can be predators and prey. They can be long-distant migrants, linking us to the rest of the world, or ultra local.
This is why I and the many others who love birds are so grieved by the threat posed by bird flu – even though we do not yet know which species will be worst affected.
After a morning with no birds, I’m buoyed by the sight of close to sixty galahs on the lawns of the National Library. I watch as they deftly extract and eat the corms of onion grass, an invasive weed.
I take some hope in the fact Australian birds are resilient, having carved out niches on the driest inhabited continent for many millions of years. It was here the world’s songbirds and parrots evolved before spreading across the globe.
Bird flu will do much damage. But we can help them recover by tackling other threats. There will always be birds. There must always be birds.
