Mound-building behaviour of a keystone bioturbator alters rates of leaf litter decomposition and movement in urban reserves

Bioturbation, the disturbance of soil and litter by digging animals plays an important role for a variety of species and ecological processes in many ecosystems. The majority of studies globally on the ecosystem engineering effects of digging vertebrates have focussed on mammals, with birds, reptiles and amphibians remaining comparatively understudied. The loss of ecosystem engineers is a key conservation challenge, and the return of these species is increasingly seen as a priority for habitat restoration; yet this concept is highly novel when we consider urban ecosystems. The Australian brush-turkey (Alectura lathami), historically a rainforest bird and now common in urban ecosystems, displaces significant quantities of soil and leaf litter through its foraging and nest-building behaviour and has previously been described as an ecosystem engineer. Here, we tested the effect of brush-turkey nest building on the decomposition rate of leaf litter, an important ecosystem process. We placed mesh bags of dried Angophora costata and Lantana camara leaves at increasing distances from brush-turkey incubation mounds. We predicted that leaf litter closer to the nest would break down faster during the brush-turkey breeding season due to increased turnover associated with nest mound maintenance. We found slower leaf litter decomposition in the breeding than the non-breeding season, but a relatively greater rate of decomposition closer to the mound in the breeding season. Our results show a seasonal difference in the spatial pattern of leaf litter decomposition and movement; we interpret that brush-turkey mound-building behaviour was the key driver. The ecosystem services provided by brush-turkeys are of particular interest for future research as this species is naturally recolonizing areas where it has been absent for decades, including urban areas. The effect of this species on ecosystem processes including nutrient cycling, seedbank stimulation and reduced fuel loads warrants further investigation.