The earthen mounds built by a chicken-like bird in Australia aren’t just incubators for eggs – they may also be necessary to distribute key nutrients throughout the ecosystem.
In the dry woodlands of South Australia, sandy mounds rise among patches of bushy ‘mallee’ eucalyptus trees. These footprints—large enough to damp parking spaces—are painstakingly constructed nests of elephant birds. By engineering a mixture of nutrients and inadvertently churning soil, the prowler may shape communities of plants and surrounding soil and even limit the spread of fire, researchers report March 27. Ecology Journal.
These ecosystem effects suggest that conservation of predatory birds could benefit many species, says Heather Neely, an ecologist with the Australian Landscape Trust at Calperum Station. This species is currently listed as “vulnerable” and declining by the International Union for Conservation of Nature.
Some animals – called “ecosystem engineers” – produce habitats for other species by shaping the environment around them. Beavers build dams that create homes for life forms in ponds. In deserts, owls and giant lizards support plant and animal life with their burrows (SN: 10/8/19; SN: 1/19/21).
“In Australia in particular, the focus has been largely on our group of crater mammals,” says Neely.
but the lie (Bake Alasellata) – found throughout western and southern Australia – also disturb the soil. They and their close relatives are the “megapodes,” a group of birds native to Australia and the South Pacific that have an unusual habit of incubating their eggs like an alligator: in a huge pile of rotting manure. Heat from decaying vegetation — trapped by an insulating sand layer on top — regulates the eggs’ temperature, and the young scratch their way to the surface upon hatching.
Neilly and her colleagues wanted to investigate the effect of nest building on soil chemistry and vegetation in the Mallee ecosystem.
In the Male Forest in rural South Australia, the team selected 12 hills of different ages. Each mound had five “mini-sites” – the mound itself, the ground under a nearby eucalyptus tree and under a distant tree, and a plot of land near and far. At each small site, the team analyzed nutrients in the soil and measured vegetation cover, abundance of individual plants and the relative cover of leaf litter and bare ground.
Many of the Maleli’s forests are nutrient poor, with islands of resources where eucalyptus trees germinate. The team found that when poultry collect leaf litter from plant patches to form their mounds in open areas, they create a unique type of habitat patch. The nests contain little plant life, but their soil has levels of carbon and pH similar to those of micro-tree sites. The hills also have higher levels of nitrogen and phosphorous in their soil than any other microsite.
The effects are not limited to the hills themselves. Even nearby open sites have higher soil phosphorous than remote sites, and nearby tree sites less than six years old have more barren areas due to foliage harvesting.
The team says that many features of these ridges decline with age, with the exception of soil carbon, which remains enhanced in the oldest ridges.
The impact of predatory birds on nutrient distribution is not surprising “given the huge amount of soil and litter these birds displace when building their mounds,” says Michelle Low, a plant ecologist at Germany’s University of Bayreuth based in Johannesburg who was not involved in the research.
But the scale of the predatory bird’s impact is surprising, as is the fact that the effect can be traced even to the surrounding open, woody microsites, says Ursulia Falco, a plant ecologist at the Center for Environmental Research in Budapest, who was also not involved in the research.
“This way the birds create three new types of micro-sites in an already mosaic system, which is great,” she says.
Malleefowl is not just about mixing soil nutrients and vegetation patterns. Nellie and her team note that the surrounding hilltops and bare patches have very little fuel to start the fires, so the ferocious birds may also help regulate the spread of fire in the Maleli forests.
Previous research by Neilly’s team also found that mounds are widely used by Australian animals. Vertebrate animals visited hills 50 percent more often than unstacked sites, with five times the number of vertebrate species hanging around hills.