Biology subjects

Bourne, A. R.

Publications and source records attributed to Bourne, A. R..

6 recordsLinked to original sources

bioRxiv2025

The emerging threat of hot drought in Western Australia

Droughts severely affect our environments, biodiversity, production systems and communities. When assessing droughts, we generally consider deficits in rainfall, subsurface water, water for crops and water for societies, economies and the environment. Due to climate change, increasing temperatures and more frequent and prolonged drought events are occurring in Australia and globally. When droughts and extreme temperatures occur together in the same space and time, it results in hot droughts, a phenomenon that can be devastating for flora, fauna and society. Here, we map hot drought events across Western Australia since 1889. Our results indicate that significant hot droughts have become more frequent, with the most severe hot droughts on record occurring within the last five years. Additionally, hot droughts within the last four decades, and particularly within the last two decades, affected a significantly larger area than the average for the historical record. With 2024 already on track to be the driest and hottest year on record in southwest Western Australia, natural resource managers must prepare for the increasing frequency and severity of hot droughts. Implication for ManagersO_LIAustralia and the world are experiencing more frequent and intense droughts and heatwaves. Hot droughts, characterised by simultaneous extreme water scarcity and extreme high temperatures, are particularly devastating. C_LIO_LIWe mapped hot drought events in Western Australia since 1889, revealing a recent surge in occurrence concentrated in the most recent five years. Statistical testing indicates that hot droughts within the most recent 20 and 40 years were significantly larger in extent compared to the historical average. C_LIO_LIWith the first half of 2024 exceptionally dry and hot, proactive strategies are imperative for natural resource managers. C_LI

ecology↗

bioRxiv2021

Hot days are associated with short-term adrenocortical responses in a Southern African arid-zone passerine bird.

Non-invasive methods for investigating the biological effects of environmental variables are invaluable for understanding potential impacts of climate change on behavioural and physiological stress responses of free-ranging animals. Foraging efficiency, body mass maintenance and breeding success are compromised in Southern pied babblers Turdoides bicolor exposed to air temperatures between ~35{degrees}C and ~40{degrees}C. We tested the hypothesis that these very hot days are acute stressors for free-ranging babblers by quantifying the relationship between daily maximum air temperature (Tmax) and faecal glucocorticoid metabolite (fGCM) levels. We collected naturally-excreted droppings from free-ranging pied babblers and analysed fGCM levels. Levels of fGCMs in droppings collected after 3pm were independent of same-day Tmax < 38 {degrees}C and averaged 140.25 ng g-1 Dry Weight {+/-} 56.92 ng g-1 DW (mean {+/-} SD) over this range. Above an inflection Tmax = 38 {degrees}C, however, fGCM levels increased linearly with same-day Tmax and averaged 190.79 ng g-1 DW {+/-} 70.13 ng g-1 DW. There was no relationship between Tmax on the previous day and fGCM levels in droppings collected the following morning. Group size, breeding stage, sex and rank did not predict variation in fGCM levels. These results suggest that very high Tmax may be linked to acute, but not chronic, heat stress responses. The fGCM levels we measured are likely to represent a biologically meaningful response to an environmental stressor (high Tmax), suggesting a physiological mechanism underlying observed changes in behaviour and reproductive success at high temperatures in this species.

physiology↗

bioRxiv2021

Direct and indirect effects of high temperatures on fledging success in a cooperatively breeding bird

High temperatures and low rainfall consistently constrain reproduction in arid-zone bird species. Understanding the mechanisms underlying this pattern is critical for predicting how climate change will influence population persistence and to inform conservation and management. In this study, we analysed Southern Pied Babbler Turdoides nestling survival, daily growth rate and adult investment behaviour during the nestling period over three austral summer breeding seasons. High temperatures were associated with lower body mass, shorter tarsi, and reduced daily growth rates of nestlings. Piecewise structural equation modelling suggests that direct impacts of temperature had the strongest influence, followed by changes in provisioning rates by adults to older nestlings. Adjustments to adult provisioning strategies did not compensate for direct negative effects of high air temperatures on nestling body mass, tarsus and wing length, or daily growth rates. Declining reproductive success during hot weather poses a potentially serious threat to population replacement and persistence as climate change progresses, even for currently common and widespread species. Significantly lower offspring survival as a result of climate warming will likely contribute to the collapse of animal communities well before temperatures regularly approach or exceed lethal tolerance limits. Detailed mechanistic data like these allow us to model the pathways by which high temperature causes nest failure. In turn, this could allow us to design targeted conservation action to effectively mitigate climate effects.

ecology↗

bioRxiv2020

Dehydration risk, not ambient incubation, limits nest attendance at high temperatures

High air temperatures have measurable negative impacts on reproduction in wild animal populations, including during incubation in birds. Understanding the mechanisms driving these impacts requires comprehensive knowledge of animal physiology and behaviour under natural conditions. We used a novel combination of a non-invasive doubly-labelled water technique and behaviour observations in the field to examine effects of temperature, rainfall, and group size on physiology and behaviour during incubation in southern pied babblers Turdoides bicolor, a cooperatively-breeding passerine endemic to a semi-arid region in southern Africa. The proportion of time that clutches of eggs were incubated declined as air temperatures increased, traditionally interpreted as a benefit of ambient incubation. However, we show that a) clutches were less likely to hatch when exposed to high air temperatures; b) pied babbler groups incubated their nests almost constantly (97% of daylight hours) except on hot days; c) operative temperatures in unattended nests were substantially higher than air temperatures and frequently exceeded 40.5{degrees}C, above which bird embryos are at risk of death; d) pied babblers incubating for long periods of time failed to maintain water balance on hot days but not cool days; and e) pied babblers from incubating groups did not maintain body mass on hot days. These results suggest that, rather than taking advantage of opportunities for ambient incubation, pied babblers leave the nests during hot periods to avoid dehydration as a consequence of incubating at high operative temperatures. As mean air temperatures increase and extreme heat events become more frequent under climate change, birds will likely incur greater water costs during incubation, leading to compromised nest attendance and increased likelihood of eggs overheating, with implications for nest success and, ultimately, population persistence.

ecology↗

bioRxiv2020

Hot droughts compromise interannual survival across all group sizes in a cooperatively breeding bird

Increasingly harsh and unpredictable climate regimes are affecting animal populations around the world as climate change advances. One relatively unexplored aspect of species vulnerability to climate change is whether and to what extent responses to environmental stressors might be mitigated by variation in group size in social species. We used a 15-year dataset for a cooperatively-breeding bird, the southern pied babbler Turdoides bicolor, to determine the impact of temperature, rainfall, and group size on body mass change and interannual survival in both juveniles and adults. Hot and dry conditions were associated with reduced juvenile growth, mass loss in adults, and compromised survival between years in both juveniles (-86%) and adults (-60%). Individuals across all group sizes experienced similar effects of climatic conditions. Larger group sizes may not buffer individual group members against the impacts of hot and dry conditions, which are expected to increase in frequency and severity in future.

ecology↗

bioRxiv2020

High temperatures drive offspring mortality in a cooperatively breeding bird

An improved understanding of life history responses to current environmental variability is required to predict species-specific responses to anthopogenic climate change. Previous research has suggested that cooperation in social groups may buffer individuals against some of the negative effects of unpredictable climates. We use a 15-year dataset on a cooperative-breeding arid-zone bird, the southern pied babbler Turdoides bicolor, to test i) whether environmental conditions and group size correlate with survival of young during three development stages (egg, nestling, fledgling), and ii) whether group size mitigates the impacts of adverse environmental conditions on reproductive success. Exposure to high mean daily maximum temperatures (mean Tmax) during early development was associated with reduced survival probabilities of young in all three development stages. No young survived when mean Tmax > 38{degrees}C across all group sizes. Low reproductive success at high temperatures has broad implications for recruitment and population persistence in avian communities given the rapid pace of advancing climate change. That impacts of high temperatures were not moderated by group size, a somewhat unexpected result given prevailing theories around the influence of environmental uncertainty on the evolution of cooperation, suggests that cooperative breeding strategies are unlikely to be advantageous in the face of rapid anthropogenic climate change.

ecology↗