The earthen heaps formed by a chicken-like bird in Australia aren’t simply egg incubators; they may also be important for the delivery of essential nutrients throughout the environment.
In South Australia’s arid forests, sandy mounds rise amid areas of many-stemmed “mallee” eucalyptus trees. These massive constructions, large enough to suffocate a parking space, are malleefowl nests, painstakingly built by the malleefowl bird. Researchers report in the Journal of Ecology that the industrious malleefowl may be changing nearby plant and soil ecosystems and perhaps blunting the spread of fire by accidentally building a patchwork of nutrients and churned dirt.
According to Heather Neilly, an ecologist at the Australian Landscape Trust in Calperum Station, such ecosystem impacts suggest malleefowl protection could benefit numerous species. The International Union for Conservation of Nature has classified the species as “vulnerable” and dwindling.
Some animals, known as “ecosystem engineers,” create habitats for other species by modifying their surroundings. Beavers construct dams that serve as houses for pond-dwelling lifeforms. With their tunnels, owls and gigantic lizards support plant and animal life in deserts.
The team chose 12 mounds of varied ages in a mallee woodland in rural South Australia. Each mound contained five “microsites”: the mound itself, the land beneath a close eucalyptus tree and beneath a distant tree, and a nearby and distant open piece of ground.
“In Australia in particular, the focus has largely been on our array of digging mammals,” Neilly says.
However, malleefowl (Leipoa ocellata), which can be found throughout western and southern Australia, also disturb the soil. They and their close cousins are “megapodes,” a group of birds native to Australasia and the South Pacific that have the odd habit of incubating their eggs in a vast pile of rotting compost, much like alligators do. Heat from decaying vegetation regulates the temperature of the eggs, which is held in by an insulating sand layer on top, and the young scratch their way to the surface upon hatching.
Neilly and her colleagues wanted to investigate the impact that nest building has on soil chemistry and vegetation cover in the mallee ecosystem.
The team chose 12 mounds of varied ages in a mallee woodland in rural South Australia. Each mound contained five “microsites”: the mound itself, the land beneath a close eucalyptus tree and beneath a distant tree, and a nearby and distant open piece of ground. The researchers studied soil nutrients and quantified plant cover, abundance of individual plants, and the relative cover of leaf litter and bare ground at each microsite.
Much of the mallee woodland is nutrient-deficient, with resource islands where eucalyptus trees flourish. The scientists discovered that when malleefowl take leaf litter from plant patches to form their mounds in open areas, they generate a unique type of habitat patch. The nests have little plant life, but their soil has carbon and pH levels like those of tree microsites. Mounds also have nitrogen and phosphorus levels in their soil that are higher than any other microsite.
The effects extend beyond the mounds themselves. Even adjacent open sites have higher soil phosphorus than farther away ones, and neighboring tree sites that are less than six years old have more bare land due to leaf litter harvesting. The team notes that many of these mound properties drop with age, with the exception of soil carbon, which remains elevated in the oldest mounds.
The impact of malleefowls on nutrient distribution is unsurprising “given the huge quantity of soil and litter that these birds displace when building their mounds,” says Michelle Louw, a plant ecologist at the Germany’s University of Bayreuth who is based in Johannesburg and was not involved in the research.
However, the size of the malleefowls’ impact is surprising, as is the fact that the effect can be traced even in nearby open and woodland microsites, according to Orsolya Valkó, a plant ecologist at the Center for Ecological Research in Budapest who was not involved in this study.
“Three new microsite kinds are created by the birds in an already mosaic system, which is intriguing,” she explains.
Malleefowl are doing more than just rearranging soil nutrients and vegetation patterns. Malleefowl may also help restrict the spread of fire in mallee forests, according to Neilly and her team, because the tops of the mounds and adjacent bare patches have relatively little fuel for fires to burn.
Neilly’s team previously discovered that the mounds are regularly frequented by Australian animals. Mounds were visited by vertebrate creatures 50% more frequently than nonmound areas, with five times as many vertebrate species congregating around the mounds.