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Climate change means bigger bills, ears and tails for 'shape shifting' animals

[Sept 7, 2021: Miki Perkins]

A red-rumped parrot, one of the bird species that has seen its bill size increase. (CREDIT: Ryan Barnaby)

Climate change is causing some animals to “shape shift” and grow larger extremities such as beaks, ears and tails, an Australian review of global scientific research has revealed, as the creatures adapt to hotter temperatures.

The study, by Deakin University bird expert and PhD student Sara Ryding, shows these changes have been occurring across wide geographical regions and among an array of unrelated, warm-blooded species.

“Shape-shifting does not mean that animals are coping with climate change and everything is fine,” Ms Ryder said.

“One of the most surprising and alarming aspects of this research is that the climate change humans have caused is forcing animals to make drastic changes over a short period of time.”


Ms Ryder said that because climate change is a complex and multifaceted phenomenon, it has been difficult to pinpoint just one cause of the shape-shifting.

Her review of previously published scientific papers, available on Wednesday in Trends in Ecology and Evolution, shows shape-shifting has been particularly reported in birds. This has significant implications for those birds that have evolved unique beaks to feed on particular types of food.

A thermal image of a king parrot shows heat coming off its beak. Some animals use their appendages - beaks, ears, tails - to release excess heat. (CREDIT: GLENN TATTERSALL, BROCK UNIVERSITY)

Several species of Australian parrot have shown, on average, a 4 to 10 per cent increase in bill size since 1871, which is positively correlated with the summer temperature each year.

North American dark-eyed juncos, a small songbird, also had a link between increased bill size and short-term temperature extremes in cold environments.

There have also been reported changes in mammalian species, including tail length increases in wood mice, and tail and leg size increases in masked shrews. Animals can divert blood flow to non-insulated appendages such as beaks, ears and legs to shed excess body heat.


It has long been that temperature can lead to patterns in overall body shape. According to a 19th century zoological law known as Allen’s rule, animals that live close to the equator tend to have larger extremities, so as to radiate heat, while animals close to the poles need to retain heat so have smaller extremities.

A Galapagos sea lion releasing heat through its front flippers. (CREDIT:GLENN TATTERSALL, BROCK UNIVERSITY)

Climate change adaptation is often discussed as a human problem, but animals are also having to adapt over a far shorter timescale than has occurred throughout evolutionary time, Ms Ryder says.

While the increases in appendage size seen so far are quite small – less than 10 per cent – prominent appendages such as ears are predicted to increase, says Ms Ryder.

Ms Ryder started her research two years ago with collaborators at the Australian National University and Brock University in Canada, who looked at how bird beaks are used in regulating body temperature.

For more science news stories check out our New Discoveries section at The Brighter Side of News.


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