How a mound-building bird is shaping its Australian ecosystem

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The piles of soil built by a chicken-like bird in Australia aren’t just egg incubators – they can also be crucial for the distribution of key nutrients throughout the ecosystem.

In the dry forests of southern Australia, mounds of sand rise between patches of multi-stemmed ‘mallee’ eucalyptus. These monuments – large enough to smother a parking space – are nests, painstakingly constructed by the malleefowl bird. By inadvertently designing a patchwork of nutrients and dirt, the industrious malleefowl could shape surrounding plant and soil communities and even dampen the spread of fire, researchers report March 27 in the Journal of Ecology.

Such ecosystem impacts suggest that conserving malleefowls could benefit many species, says Heather Neilly, an ecologist at the Australian Landscape Trust at Calperum Station. The 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 the life forms living in the ponds. In deserts, owls and giant lizards support plant and animal life with their burrows (SN: 08/10/19; SN: 01/19/21).

“In Australia in particular, the focus has been largely on our range of burrowing mammals,” says Neilly.

But the males (Leipoa ocellata) – found in western and southern Australia – also disturb the soil. They and their close relatives are “megapodes”, a group of poultry native to Australasia and the South Pacific that have the unusual habit of incubating their eggs much like alligators do: in a huge pile of rotting compost . The heat from the decaying vegetation – trapped by an insulating layer of sand on top – regulates the temperature of the eggs and the young make their way to the surface when they hatch.

Neilly and his colleagues wanted to study the impact of nest building on soil chemistry and ground cover in the mallee ecosystem.

In a mallee forest in rural South Australia, the team selected 12 mounds of varying ages. Each mound had five “microsites” – the mound itself, the ground under a nearby eucalyptus and under a distant tree, and a near and far open patch of land. At each microsite, the team analyzed nutrients in the soil and measured ground cover, the abundance of individual plants, and the relative cover of leaf litter and bare soil.

Much of the mallee forest is nutrient poor, with resource islands where eucalyptus trees grow. But when malleefoils pick up leaf litter from vegetation patches to make their mounds in open areas, they create a unique type of habitat patch, the team found. The nests have little plant life, but their soil has carbon and pH levels like those of tree microsites. Mounds also have higher levels of nitrogen and phosphorus in their soil than any other microsite.

The impacts are not limited to the mounds themselves. Even nearby open sites have higher phosphorus soil than far sites, and sites with nearby trees less than six years old have more bare soil due to leaf litter harvesting.

Many of these mound attributes decline with age, the team reports, with the exception of soil carbon, which remains enhanced in older mounds.

Two malleefowl in the egg chamber of a mound nest
During breeding season, malleefowl burrow to the egg chamber of a mound nest, where the female lays an egg before covering it. This process repeats throughout the breeding season.Tim Pascoe

Malleefowls’ impact on nutrient distribution is not surprising “given the enormous amount of soil and litter these birds displace when building their mounds,” says Michelle Louw, a plant ecologist at the German University of Bayreuth, based in Johannesburg and was not involved in the research.

But the scale of malleefowl impact is startling, as is the fact that the effect is traceable even in surrounding open and wooded microsites, says Orsolya Valkó, a plant ecologist at the Budapest Center for Ecological Research, also uninvolved. in this research.

“In this way, the birds create three new types of microsites in an already mosaic system, which is fascinating,” she says.

Malleefowl don’t just mix soil nutrients and vegetation patterns. Neilly and his team note that mound tops and surrounding bare areas have very little fuel for fires, so waterfowl can also help regulate fire spread in mallee forests.

Previous research by Neilly’s team also revealed that mounds are widely used by Australian wildlife. Vertebrate animals visited mounds 50% more frequently than non-mounded sites, with five times as many vertebrate species hanging around mounds.

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