Global warming is a big challenge for warm-blooded animals, who need to maintain a constant internal body temperature. As anyone with heat stroke can tell you, our bodies become severely stressed when we warm up.
Animals face global warming in several ways. Some move to colder areas, such as closer to the poles or to higher ground. Some change the timing of key vital events, such as breeding and migration, so that they take place in cooler times. And others evolve to change body size to cool down faster.
Our new research examined another way animal species cope with climate change: resizing their ears, tails, beaks, and other appendages. We reviewed the published literature and found examples of animals that increased appendix size in parallel with climate change and associated temperature increases.
In doing so, we identified multiple examples of animals that are likely to change shape, including species in Australia. The pattern is widespread and suggests that global warming may cause fundamental changes in animal form.
Following Allen’s rule
It is well known that animals use their appendages to regulate their internal temperature. African elephants, for example, pump hot blood into their large ears, which they then beat to disperse the heat.
The beaks of birds have a similar function: blood flow can be diverted to the bill when the bird is hot. This heat dissipation function is represented in the thermal image of a real parrot below, which shows that the beak is warmer than the rest of the body.
All this means that there are advantages in larger appendages in warmer environments. In fact, since the 1870s, the American zoologist Joel Allen noted in colder climates that warm-blooded animals – also known as endotherms – tended to have smaller appendages, while those in warmer climates warm ones usually have larger ones.
This pattern became known as the Allen rule, which has since been supported by studies of birds and mammals.
Biological patterns such as Allen’s rule can also help make predictions about the evolution of animals as the climate warms. Our research set out to find examples of animal shape changes over the past century, consistent with global warming and the Allen rule.
What animals are changing?
We found more documented examples of shape changes related to birds, specifically, beak size increases.
This includes several species of Australian parrots. Studies show that the beak size of gangster cockatoos and red-necked parrots has increased by 4 to 10 percent since 1871.
Mammalian appendages also increase in size. For example, in the masked shrew, the length of the tail and leg has increased significantly since 1950. And in the large round-leaved bat, the size of the wings increased by 1.64 percent during the same period.
The variety of examples indicates that the change of form is taking place in different types of appendages and in various animals, in many parts of the world. But more studies are needed to determine which types of animals are most affected.
A red yellow parrot, a species that increases its beak size in response to climate change. (Ryan Barnaby)
Other uses of the appendices
Of course, animal appendages have uses far beyond body temperature regulation. This means that scientists have sometimes focused on other reasons that may explain changes in the body shape of animals.
For example, studies have shown that the average beak size of the Galapagos finch has changed over time in response to seed size, which in turn is influenced by rainfall. Our research examined previously collected data to determine whether temperature also influenced changes in the beak size of these finches.
These data show that rainfall (and, by extension, seed size) determines beak size. After drier summers, the survival of small-billed birds was reduced.
But we have found clear evidence that birds with smaller beaks are also less likely to survive warmer summers. This effect on survival was stronger than that observed with precipitation. This indicates that the role of temperature may be as important as other uses of the appendages, such as food, in modifying the size of the appendages.
Our research also suggests that we can make predictions about which species are most likely to change the size of the appendix in response to rising temperatures, that is, those that adhere to Allen’s rule.
These include (with some caveats) starlings, songbirds, and a large number of seabirds and small mammals, such as the South American slender opossums.
Why does shape change matter?
Our research contributes to the scientific understanding of how wildlife will respond to climate change. In addition to improving our ability to predict the impacts of climate change, this will allow us to identify which species are most vulnerable and require conservation priority.
Last month’s report from the Intergovernmental Panel on Climate Change showed that we have very little time to avoid catastrophic global warming.
While our research shows that some animals adapt to climate change, many will not. For example, some birds may have to maintain a particular diet, which means they cannot change the shape of their beak. Other animals may not be able to evolve over time.
Therefore, while it is important to predict how wildlife will respond to climate change, the best way to protect species in the future is to drastically reduce greenhouse gas emissions and avoid as much global warming as possible. 
Sara Ryding, PhD candidate, Deakin University and Matthew Symonds, associate professor at Deakin University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.