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Weighing the cost: the impact of heatwaves on birds

Models predict more frequent catastrophic mortality events for Australia’s arid zone birds under future climate scenarios.  Innovative new science using TERN data has, for the first time, tested these predictions and documented the impact of extreme heat on a wild population of Australasian robins.
 

Rising temperatures and more intense heatwaves pose a grave risk to birds which call Australia’s arid zone home, says Dr Lynda Sharpe of the Australian National University (ANU).
 

“Desert dwelling bird species already live close to their physiological limits. As temperatures rise, they’re balanced on a knife edge between the need to conserve water and the need to use it for evaporative cooling.

A wild jacky winter exhibiting symptoms of dehydration after a heatwave (image courtesy of Janet Gardner)

If heat exposure is too great, or too prolonged, birds succumb to lethal dehydration or over-heating, and mass die-offs have already been observed”
 

Dr Lynda Sharpe

To predict how global warming and intensifying heatwaves will impact upon arid zone birds, researchers have developed models based on the physiological responses of captive birds to high temperatures.  These models predict that catastrophic mortality events will become more frequent under future climate scenarios, particularly within Australia, but it remains unclear whether the lab-based findings apply to wild populations.

Extreme heat’s extreme impacts

To quantify the impacts of heat exposure on wild populations, and validate the models, the team of researchers from ANU’s Division of Ecology and Evolution has assessed the effects that extreme heat has on a wild population of jacky winters (Microeca fascinans)—a small grey-brown robin, common throughout much of Australia.

A wild jacky winter perched on a balance for weighing (image courtesy of Janet Gardner)

Every day during a series of severe heatwaves in the summer of 2018-19, they monitored the change in the weight of individual jacky winters.  Conducting their research at TERN’s Calperum Mallee SuperSite in South Australia, Dr Sharpe and her colleagues compared the body mass data with the micro-meteorological data collected by the site’s eddy-covariance flux tower.
 

“We found that as daily maximum temperature and duration of heat exposure increased, the birds’ ability to maintain body mass decreased.”

At temperatures above 42°C, birds lost around 2% of their body mass every day and all breeding birds abandoned their nests. Mortality increased almost three-fold over the summer heatwave period.”

Dr Lynda Sharpe

Field experiment results not as dire as model predictions

Despite the team’s frightful findings, the research seems to have a silver lining.  Fellow researcher Dr Janet Gardner says that the daily weight losses they recorded in the field were less than the lab-based models predicted.
 

A wild jacky winter engaging in heat dissipation behaviour (image courtesy of Janet Gardner)

“We believe this is because the wild jacky winters were able to regulate their body temperature via behaviours such as selecting sites that facilitate convective cooling, like elevated perches that catch the wind for ‘wind-surfing’; and by withdrawing to cooler microhabitats to avoid the worst temperatures.

We also found that wild birds were able to recuperate more quickly than expected and regain some mass between heatwave events.”
 

Dr Janet Gardner

Although the study documents the effects of extreme heat on just one population of a single species, the research results suggest that wild birds may be less severely affected, and more able to recuperate, than anticipated.  Research is ongoing…

  • Data from TERN’s Calperum Mallee SuperSite and all other TERN Ecosystem Processes monitoring sites are openly available for download via the TERN Data Discovery Portal.
  • For more information on this research using TERN please contact Janet Gardner.

Data on the exchanges of energy, carbon and water between the ground and atmosphere, as well as detailed soil and vegetation data, have been collected at TERN’s Calperum Mallee SuperSite (above) since 2012 and are openly available via TERN

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