Global warming is reshaping our planet. It intensifies hurricanes, causes more fires and dries up rivers. Now, scientists are finding that climate change is also turning animals into shape-shifters. Many creatures are changing the sizes and shapes of certain body parts. Some are growing bigger wings, some are sprouting longer ears and others are growing larger bills. These changes aren't happening at random, scientists say. Animals are undergoing them to better regulate their body temperatures—basically to cool off.
A group of scientists at Deakin University in Australia, along with collaborators at Brock University in Canada, have traced how about 30 species changed across various timeframes in response to rising temperatures. In their work, they combed through nearly 100 previous studies by other researchers, some based on field work, some on laboratory experiments and others on vast museum collections that preserved, catalogued and measured animal specimens for decades. The researchers tracked comparisons that date back a century or two in some cases. They and published their findings in the journal Trends in Ecology and Evolution.
“As a meta analysis it was a very impressive effort,” says ornithologist Ben Winger at the University of Michigan who studied similar topics but wasn’t involved in the study. The findings unveil new insights about how our planet’s warm-blooded neighbors are dealing with rising temperatures.
Unlike humans, warm-blooded animals in the wild don’t enjoy the luxuries of air-conditioning so they have to rely on their own bodies to avoid overheating. They release heat through their appendages, explains Sara Ryding, the study’s author. For little creatures like mice, tails do the job. For birds, their bills do the work. And elephants rely on their massive ears to stay cool. In videos of elephants roaming through the African landscapes, their ears periodically flail back and forth, releasing excess heat in the air. “It is a well-documented fact that elephants cool off through their ears,” Ryding says.
Although elephants weren’t part of Ryding’s study, her team found that over various times periods Australian parrots increased the sizes of their bills, Chinese roundleaf bats grew bigger wings, European rabbits sprouted longer ears and mice lengthened their tails. “Parrots were a particularly great example because many studies looked at them,” says Ryding. “That’s because museums have extensive collections and records of birds, dating back to the 1800s, and sometimes even older.” Thanks to this data, the team found that since 1871, parrots grew their beak surface area 4 to 10 percent. The roundleaf bat collection included 65 years worth of museum specimens, which let the team conclude that they increased their wing size by more than 1 percent since the 1950s.
The animals’ shapes-shifting changes make sense, researchers say. In biology, an established concept called Bergmann's rule states that creatures that live in colder climates tend to be larger and thicker than those closer to the equator—to better conserve heat. The rule is named after Carl Bergmann, a nineteenth century biologist who first described the pattern in 1847. Thirty years later, another biologist, Joel Asaph Allen further expanded the concept, stating that animals that adapted to cold climates have shorter limbs and bodily appendages—to keep the warmth in. For similar thermoregulatory reasons, the reverse is also commonly true—in hotter climates warm-blooded animals’ appendages become larger, relative to their body size.
Larger appendages like bills, ears, tails and even wings can help animals dissipate more heat into the surrounding air. In a somewhat crude comparison, an apartment radiator works in a similar way. A big radiator with a large surface area would release more heat into a room compared to a smaller one. On thermal photos of parrots, one can see the heat radiating from their beaks and talons, which are glowing bright yellow. Bigger appendages also allow growing larger vasculature that brings more blood, and thus more body heat to dispel. “According to the Allen’s rule, you have an increased amount of surface area of your appendage,” explains Ryding. “And for animals it means that when you are pumping blood into a certain appendage there’s more surface area where the heat can be lost.”
Ryding’s team also plowed through various field studies. One of them measured the bills of Galapagos finches from 2003 to 2011 and found that they enlarged in response to temperature spikes. “Galapagos finches increase their bills depending on the temperatures of the preceding year and they fluctuate a little bit,” Ryding says. Other data the researchers analyzed focused on European rabbits, which were brought to Australia and settled in areas with different weather. Those that found themselves in hotter spots developed longer ears over time. “It’s a really interesting example of how animals respond to differences in their ambient temperate after they been introduced elsewhere,” she says.
The team also found that Japanese quails, raised in laboratory settings that were hotter than their typical habitat temperatures, grew longer beaks, adjusting to the environmental changes in just one generation. Similarly, lab mice grew up with longer tails. It’s a much shorter time frame than museum or field studies, Ryding notes, and it shows that the animals can really adapt to their environments very quickly.
However, the researchers aren’t sure whether this shape-shifting is a good development or not. “It’s hard to tell what the consequences are,” says Winger. “It depends on whether these these adaptations are able to keep pace with other environmental aspects and what implications they have for finding food or avoiding predators.”
If larger ears or bills can help the animal cool off instead of overheating and dying, that’s a good thing. But certain changes may interfere with some creatures’ ability to forage. For example, for birds that feed on flower nectar, having small narrow beaks is important. “If you are a hummingbird and your beak is getting broader and wider, it may become too large to effectively feed on flowers where you are drawing your nutrition from,” says Ryding—causing the birds to become malnourished. So shape-shifting does not mean that animals are coping with climate change well, Ryding says. It just means that they are evolving to withstand it. Whether this will help them survive and thrive in the long run is less clear.
What’s clear is that the future temperature increases will turn more animals into shape-shifters, a description that evolutionary ecologist Raymond Danner at University of North Carolina, Wilmington finds not only fitting, but vivid. “The shape-shifting term is a great visual of animals changing over time in how they respond to the environmental challenges,” says Danner who also wasn’t involved in the study, but had done similar work. He adds that the study did a good job of synthesizing the growing body of evidence on this subject. “And perhaps more importantly, it showed how by re-analyzing a few datasets we can design studies to better understand shape-shifting in the future.”