Birds in Israel Are ‘Shape-shifting’ Due to Global Warming, Study Finds
Tel Aviv University researchers find morphological changes in more than half of bird species that enable them to better cope with heat
Birds in Israel have changed their body shapes in the past 70 years as a result of global warming, researchers have found.
In a comprehensive study, researchers at Tel Aviv University examined roughly 8,000 adult bird specimens from 106 different species – including migratory birds that pass through Israel annually – and found that the bodies of more than half of them had become either longer or thinner in recent decades. The body mass of some species decreased, while the body length of others increased, thereby boosting the ratio between surface area and volume.
Researchers believe these changes could be a way for birds to shed heat as temperatures rise.
Professor Shai Meiri of Tel Aviv University’s School of Zoology led the study together with doctoral student Shahar Dubiner and the Steinhardt Museum of Natural History in Tel Aviv. The findings were recently published in the scientific journal Global Ecology and Biogeography.
Meiri told The Media Line that the researchers relied on the Steinhardt Museum’s extensive collection of specimens to conduct their research.
“What surprised us was that there were seemingly two ways for birds to change: either reduce their weight or increase their length,” Meiri said. “We had a vague notion that climate change may be doing something, now we may have more reason to think that it may be making things worse. It calls for further research; it certainly is not a happy finding.”
Using a complex statistical model, the scientists found that the mass of birds decreased by 18.3%, their length increased by 5.1%, and their surface-area-to-volume ratio increased by 28.9% over the last 70 years. Significantly, the latter increase also corresponds to a 12.2% raise per degree Celsius in warming.
Researchers saw these changes in Israeli non-migratory birds as well as migratory birds coming from Europe, Asia, and Africa, suggesting that the phenomenon is global in nature.
“We can’t say yet that [birds are] in danger, but they are changing,” Meiri said. “If they’re changing and becoming thinner it may well be that they are in worse physical condition. This is certainly pointing to a potential danger, but it needs further verification.”
Meiri explained that, according to Bergmann’s rule, which was first posited in the 19th century, birds and mammal species living in cold climates tend to be larger than members of the same species living in warmer climates. This is due to the fact that the bodies of smaller animals permit more heat loss, which is an advantage in warmer areas, whereas those living in colder climates tend to have larger bodies in order to minimize heat loss.
Based on this rule, scientists have predicted that global warming would lead to a reduction in animal size, with some exceptions.
Dubiner, who also led the study, told The Media Line that the study ultimately provides evidence of how climate change is already affecting organisms and their morphology.
“The importance was to show unequivocally that this is how birds are being affected and that there is a strong link to climate change,” Dubiner said. “Now that this question has pretty much been answered we can transition to trying to understand the consequences.”
The findings further raise concerns that birds will be unable to keep adapting to rising temperatures, and will run out of effective solutions as the planet heats up. Meiri and Dubiner hope that other experts will use their research for future study.
“Our findings indicate that global warming causes fast and significant changes in bird morphology,” Dubiner said. “There are limits to how much birds can keep changing and we need to understand what happens if selection pressures start to build up. Each species reacts very differently to temperature differences.”