Common ringtail (Image: James Turner)
Hot Topic

The impacts of heatwaves on Australia’s wildlife

Tuesday, 8 December 2020  | 

Author: James Turner (Charles Sturt University),

Heatwaves are predicted to increase in frequency, duration and intensity in Australia [5]. Although brief, they cause mass wildlife die-offs and long-lasting ecological changes, such as reduced body condition of populations [4, 6, 8]. During heatwaves, air temperatures rise above normal maxima for several days, placing many species at risk of heat stress [10, 18]. Individuals at geographic range edges may be under considerable threat, because these areas often have climates at the limit of a species’ heat tolerance [7].

Research shows mammals and birds adjust their behaviour and physiology to avoid overheating. They move into shaded, cooler areas; reduce activity; change posture; or forego eating to avoid increased body temperature during digestion [1, 2]. Additionally, animals radiate heat through skin regions with many blood vessels, such as ears; sweat or spread saliva on the skin to aid evaporative cooling; pant; or allow body temperature to increase with air temperature [7, 8, 9]. When air temperature exceeds body temperature, birds and mammals can only cool themselves using evaporative water loss, which puts them at risk of dehydration and hyperthermia [13, 18]. During extreme heatwave temperatures these adaptations may not be enough, resulting in death [15, 19].

In recent summers, mass mortality has become more common [8, 19]. Bats are the most conspicuous victims—one third of the world’s spectacled flying-fox population died during one heatwave in November 2018. Heatwaves have also killed possums, koalas, three other flying-fox species, fish and at least 30 bird species. Currently, only emergency solutions for reducing impacts exist, such as providing animals with water, food or shelter [12, 14]. While these may be successful in the short-term, their usefulness relies on ongoing funding and infrastructure support. To best identify which species are at risk, and where animals can survive future temperature extremes, we need to combine physiological and behavioural data with climate predictions to find potential areas of suitable habitat [3, 10, 11].

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Research Entries

[1] Beale, P.K., Marsh, K.J., Foley, W.J., and Moore, B.D. (2018). A hot lunch for herbivores: physiological effects of elevated temperatures on mammalian feeding ecology. Biological Reviews 93, 674-692.
A review of the literature describing the influence of herbivorous diets on mammal thermoregulation and the potential implications of increasing ambient temperatures associated with climate change.
Plant secondary metabolites (PSMs) in mammal diets increase the chance of heat stress at high ambient temperature via several pathways. The ability of herbivores to process PSMs decreases with increasing ambient temperature. To avoid hyperthermia, animals must regulate their intake of PSMs, which could potentially lead to individual- and population-level changes in reproductive success. Mammalian physiological heat tolerance and plant nutritional quality are likely to be impacted by climate change, thereby changing the relationship between animals and their food.
[3] Briscoe, N.J., Kearney, M.R., Taylor, C.A., and Wintle, B.A. (2016). Unpacking the mechanisms captured by a correlative species distribution model to improve predictions of climate refugia. Global Change Biology 22, 2425-2439.
To improve predictions of climate refugia by develop a fine-scale model predicting koala distribution under various climate change scenarios using behavioural, morphological and physiological data.
The main factor driving koala distribution is the ability to fulfill water requirements during times of high ambient temperature. Model predictions can be improved by including weather variables that cause physiological stress.
[2] Briscoe, N.J., Handasyde, K.A., Griffiths, S.R., Porter, W.P., Krockenberger A., and Kearney M.R. (2014). Tree-hugging koalas demonstrate a novel thermoregulatory mechanism for arboreal mammals. Biology Letters 10, 20140235.
To describe koala tree-hugging behaviour during high ambient temperature and model the effects of this on the costs of evaporative cooling.
Koalas adjusted tree use during hot weather to maximise body heat dissipation. Tree temperature was up to 8.9°C cooler than ambient temperature. Cool tree trunks allow koalas to dump heat via convection at high ambient temperature, thereby reducing the need for evaporative cooling.
[4] Conradie, S.R., Woodborne, S.M., Cunningham, S.J. and McKechnie, A.E. (2019), Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century. Proceedings of the National Academy of Sciences 116, 14065-14070.
To assess the relative roles of lethal and sublethal high ambient temperature exposure in the decline of bird communities in a southern African desert.
Chronic exposure to hot weather will increase during the 21st century. Chronic exposure to sustained high ambient temperature results in decreased body condition, delayed fledging, smaller fledgling size and breeding failure. These consequences of chronic, sublethal exposure to high ambient temperature are more likely to drive the decline of this bird community than acute, lethal hyperthermia or dehydration suffered during heatwaves.
[5] Gardner, J.L., Amano, T., Sutherland, W.J., Clayton, M., and Peters, A. (2016). Individual and demographic consequences of reduced body condition following repeated exposure to high temperatures. Ecology 97, 786-795.
To test whether exposure to high ambient temperature affects the body condition, fitness and survival of white-plumed honeyeaters using a 26-year dataset.
Repeated exposure to high ambient temperature reduced body condition during low-rainfall conditions. Survival was lower for females and small males, which possibly drove an increase in mean body mass over time. Annual survival decreased with increasing ambient temperature and decreasing rainfall.
[6] Krockenberger, A.K., Edwards, W. and Kanowski, J. (2012). The limit to the distribution of a rainforest marsupial folivore is consistent with the thermal intolerance hypothesis. Oecologia 168, 889-899.
To determine whether the thermal physiology of green ringtail possums limits their distribution.
Possums use controlled hyperthermia at ambient temperature >30°C, which reduces evaporative water loss. Dehydration likely limits possum survival when ambient temperature exceeds 30°C for 5 hours per day for periods of 4-6 days. Possum distribution corresponds with the occurrence of high ambient temperature.
[7] McKechnie, A.E., and Wolf B.O. (2010). Climate change increases the likelihood of catastrophic avian mortality events during extreme heat waves. Biology Letters 6, 253-256.
To predict the current and future effects of extreme high ambient temperature during heatwaves on the water requirements and survival times of birds.
Heatwaves drastically increase the water requirements of small birds, leaving them vulnerable to dehydration, hyperthermia and death.
[8] McKechnie, A.E., and Wolf B.O. (2019). The physiology of heat tolerance in small endotherms. Physiology 34, 302-313.
A review of the literature on small mammal and bird heat tolerance and physiological mechanisms used to cope with high ambient temperature.
Various mechanisms are used by small mammals and birds to cope with high ambient temperature, ranging from whole-body to molecular levels. Taxon-specific heat tolerance abilities and capacities for cooling exist. Exposure to heatwaves can result in individual mortality and population declines.
[9] McKechnie, A.E., Hockey, P.A.R., and Wolf B.O. (2012). Feeling the heat: Australian landbirds and climate change. Emu 112, i-vii.
A review of the literature on the effects of heatwaves on Australia's avifauna.
Mass mortality events of Australian birds caused by extreme high ambient temperature are catastrophic and relatively common. The frequency of heatwaves in Australia is increasing. Species-specific, individual-based, physiologically-informed models are likely to be the most accurate for predicting future climate change effects.
[10] Meade, J., VanDerWal, J., Storlie, C., Williams, S., Gourret, A., Krockenberger, A., and Welbergen, J.A. (2018) Substantial reduction in thermo-suitable microhabitat for a rainforest marsupial under climate change. Biology Letters 14, 20180189.
To predict the effect of increasing ambient temperature associated with climate change on the green ringtail possum, via estimations of available suitable habitat under four greenhouse gas emission scenarios, using a model informed by thermal physiological data.
90% of species sightings occurred in areas where heatwaves (as defined by the authors) had never occurred. Up to 86% of suitable habitat could be lost by 2085.
[11] Meehl, G.A., and Tebaldi, C. (2004). More intense, more frequent and longer lasting heat waves in the 21st century. Science 305, 994-997.
To model current and future heatwave dynamics of Europe and North America
Heat waves are predicted to increase in frequency, duration and severity in the future, caused by the effects increasing greenhouse gas emissions have on the atmosphere.
[12] Mella, V.S.A., McArthur C., Krockenberger M.B., Frend, R. and Crowther M.S. (2019). Needing a drink: Rainfall and temperature drive the use of free water by a threatened arboreal folivore. PLoS ONE 14, e0216964.
To test artificial water stations as a potential tool for mitigating the effects of hot, dry weather on koalas.
Koalas used water stations year-round. Koalas spent more time drinking during times of low rainfall and water station visitation frequency increased during hot weather. Numerous other native and introduced mammal species used the water stations.
[13] Mitchell, D., Snelling, E.P., Hetem, R.S., Maloney, S.K., Strauss, W.M., and Fuller, A. (2018). Revisiting concepts of thermal physiology: Predicting responses of mammals to climate change. Journal of Animal Ecology 87, 956-973.
A literature review on how misconceptions about heat transfer and thermoregulation can influence the accuracy of models aiming to predict the affect of climate change on large mammals.
Many incorrect assumtions and misinterpreted relationships about thermal physiology are prevalent in the literature. Stemming the spread of these misconceptions will help improve model accuracy.
[14] Mo, M., and Roache, M. (online early). A review of intervention methods used to reduce flying-fox mortalities in heat stress events. Australian Mammalogy.
A literature review on intervention methods used in an attempt to help flying-foxes during heatwaves.
Various techniques are used that aim to reduce flying-fox mortality at high tempertaure, including spraying/misting vegetation, groups of bats or individuals with water; rehydration therapy; immersing animals in water; and removing animals from camps for ex situ treatment. No technique is likely to be universally effective, given variation in environmental conditions among areas. Few quantitative data are available on technique effectiveness as most published information is anecdotal.
[15] Ratnayake, H.U., Kearney, M.R., Govekar, P., Karoly, D., and Welbergen, J.A. (2019). Forecasting wildlife die-offs from extreme heat events. Animal Conservation 22, 386-395.
To develop an improved model for predicting the occurence flying-fox mortality events.
There was a significant risk of flying-fox mortality when ambient temperature reached 42°C. The model can be used to accurately predict flying-fox die-offs, and potentially other species with known thermal tolerance data, at the landscape scale. Predictions of mortality could be projected 48 hours into the future with up to 73.5% accuracy. A publicly-available website with a "flying-fox heat stress forecaster" was developed and launched in 2017.
[16] Riddell, E.A., Iknayan, K.J., Wolf, B.O., Sinervo, B. and Beissinger, S.R. (2019). Cooling requirements fueled the collapse of a desert bird community from climate change. Proceedings of the National Academy of Sciences 116, 21609-21615.
To determine whether a 50-species bird community collapse caused by climate change was driven by water required for evaporative cooling at high ambient temperature.
Birds that needed more water for cooling suffered the greatest declines. Survival was lower in birds from hotter, drier sites. Future climate change will increase the cooling costs of birds by 50-78%.
[17] Sergio, F., Blas, J. and Hiraldo, F. (2017) Animal responses to natural disturbance and climate extremes: a review. Global and Planetary Change 161, 28-40.
A literature review on how increases in natural disturbances caused by climate change and human activities are likely to affect animal behaviour, life history traits, morphology, physiology and genetic structure.
Responses to disturbances are many and varied and depend on numerous situational factors. Responses from disturbances scale up from individuals to populations and communities.
[18] Turner, J.M. (2020) Facultative hyperthermia during a heatwave delays injurious dehydration of an arboreal marsupial. Journal of Experimental Biology 223, jeb219378.
To examine the physiological responses of the common ringtail possums to heatwave exposure.
Possums let their body temperature increase at high ambient temperature to reduce water loss. When ambient temperature exceeds body temperature, possums cool themselves by rapidly increasing evaporative water loss, which could lead to physiological injury or death from dehydration with hours.
[19] Welbergen, J.A., Klose, S.M., Markus, N., and Eby, P. (2008). Climate change and the effects of temperature extremes on Australian flying-foxes. Proceedings of the Royal Society B 275, 419-425.
To describe the contribution of heatwaves to mortality events recorded for Australian flying-fox species.
Heatwaves caused 16 mass die-offs of flying-foxes since 1994. Flying-foxes used behavioural thermoregulation during a heatwave. Different species and demographic groups had varying susceptibilities to heat. Mortality events are likely when ambient temperature reaches 42°C.