The effects of the 2019-2020 megafires on koalas and the nutritional quality of their habitat

Abstract

Bushfires are a major global ecosystem disturbance, particularly in Australia's fire-prone dry sclerophyll Eucalyptus forests. Understanding the impacts of fire on wildlife ecology can facilitate the development of management actions that improve conservation outcomes for threatened species. The 2019-2020 megafires in Australia were extensive, burning thousands of hectares of eucalypt forests and killing and injuring many native animal species, including koalas (Phascolarctos cinereus), which rely on eucalypt foliage. Eucalypts can resprout after fires, potentially providing food for koalas, but the effects of fire on food quality and folivore ecology remain poorly understood during the post fire recovery period. There is also a lack of information about whether rehabilitated koalas can successfully reintegrate into burnt landscapes. This thesis addresses these key knowledge gaps. The main themes are: 1) koala health in the period following fire, 2) how fire and rehabilitation affect koala movement patterns over time, and 3) how the nutritional composition and palatability of eucalypt browse are impacted by fire in the longer term. In chapter one, I investigated the effects of fire and rehabilitation on koala health by measuring haematological and biochemical parameters, chlamydial shedding, and body condition scores of rehabilitated and non-rehabilitated koalas in burnt and unburnt landscapes at several timepoints. Most measurements were within normal ranges and similar between koala groups, demonstrating that living in burnt areas and being in care did not exacerbate disease or negatively impact koala health or body condition. In chapter two, I GPS-tracked 32 koalas for up to nine months in burnt and unburnt landscapes, measuring home ranges, mean nightly distance, farthest distance moved from release site, and total displacement distance (straight-line distance from their release location to recapture location). Rehabilitated koalas (individuals who were in care after the fires and released back to their original capture location) moved farther from their release site, had larger displacement distances, and larger home ranges than non-rehabilitated koalas, suggesting that rehabilitation, rather than living in a burnt landscape, influenced their movement patterns. In chapter three, I conducted a feeding study with four captive koalas to observe their consumption of epicormic growth from eight eucalypt species and measured foliar total and available nitrogen and two types of plant secondary metabolites (PSMs) that deter herbivory. Koalas consumed more epicormic foliage from species within the Symphyomyrtus subgenus compared to the Eucalyptus subgenus, with Symphyomyrtus species also having higher concentrations of nitrogen. These results suggest koalas are more likely to browse from Symphyomyrtus species after fire and may acquire more protein from these species. In chapter four, I sampled foliage from two eucalypt subgenera, Symphyomyrtus and Eucalyptus, in burnt and unburnt woodland over a year to observe changes in foliar chemistry. Epicormic growth initially had higher concentrations of nitrogen, which decreased over time. Concentrations of formylated phloroglucinol compounds (FPCs; compounds that deter herbivory) were also higher in epicormic growth. This demonstrates that koalas may face a trade-off when eating epicormic leaves. Collectively, my research on koala health, movements and post-fire changes in nutritional composition shows that burnt forests can be suitable habitat and provide adequate food for rehabilitated and non-rehabilitated koalas. These findings are crucial for developing informed conservation strategies to better protect koalas and other marsupial folivores in fire-prone landscapes. Policies should recognise that burnt habitat can contain valuable food resources in a relatively short timeframe and that, after animals are rehabilitated, they can be returned to their rescue location. Show more