Climate change is causing animals to 'shape shift'
During migration, the birds all died as they collided with high-rise buildings in Chicago, and the birds were gathered by the city's Field Museum.
As the planet warms, animals' beaks, legs, and ears grow larger, allowing them to better regulate their body temperatures, with birds being the most affected.
This observation has been made by Sara Ryding, a researcher at Deakin University in Australia and one of the authors of the study published in the journal Trends in Ecology & Evolution on Tuesday.
Some Australian parrot species had their beak size rise by 4% to 10% on average since 1871, the largest alterations in appendage size among the more than 30 animals studied in the research.
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"It means animals are evolving, but it does not necessarily mean that they are coping with climate change. We can see that some species have increased in appendage size so far, but we don't know if they will be able to keep up as the climate crisis worsens," Ryding told CNN.
"We also don't know whether these shape-shifts actually aid in survival (and therefore are beneficial) or not. This phenomenon of shape-shifting shouldn't be seen as a positive, but rather it is alarming that climate change is pushing animals to evolve like this, under such a relatively short timeframe."
The changes, she added, were small and unlikely to be seen right away, but they might be functionally essential.
Despite the fact that climate change is a compelling case for being the main factor behind these changes in form, the study found it impossible to establish causation with confidence due to the multiple effects climate change has on the ecosystem.
Appendages are larger on smaller bodies
Individuals in warmer areas have larger appendages, such as wings and beaks, according to Allen's rule, with the increased surface area helping the creatures to manage their temperature more readily, the study noted.
Simultaneously, body sizes tend to shrink, as smaller bodies retain less heat.
In the United States, a recent study of 70,716 migratory birds spanning 52 species found that their wingspan has widened and their bodies have shrunk during the last four decades. During migration, the birds all died as they collided with high-rise buildings in Chicago, and the birds were gathered by the city's Field Museum.
"Both of our studies look at how animals respond to climate change by altering their surface area to volume ratio," explained Ryding.
Shrews and bats have grown their relative ear, tail, leg, and wing sizes, according to the report, although most research on morphological change through time has concentrated on birds.
More research on diverse species and habitats was needed to establish how widespread the occurrence was and to anticipate which species could shape-shift in the future, according to the report.
"Previous studies have shown cases where shape-shifting is happening, but these have focused on individual species or groups. Our review paper combines all of these to show how widespread this phenomenon seems to be," Ryding said.
