MISSOULA - We live in a rapidly changing climate, where animals are being forced to adapt in peculiar ways.
This edition of A Wilder View looks at why animals are shrinking.
The mighty polar bear is now two-thirds of their size from just 30 years ago. Meanwhile, menhaden — which is a silver fish that’s widely used for animal feed and bait — has shrunk on average by 15% over the last 65 years.
But it’s not just them. Scientists have observed that birds, amphibians and mammals all are becoming smaller.
The reason for this shrinkage is climate change. As the planet heats up, many animals are finding it harder to regulate their body temperature and in order to survive, they are shrinking in size — which is impacting ecosystems and our day-to-day lives.
In 1847, zoologist Christian Bergmann made a groundbreaking observation, noticing that closely related species of mammals and birds that lived in warmer climates tended to be smaller in size. This, he reasoned, was because smaller animals have a higher surface area-to-volume ratio, meaning they lose heat faster and struggle to maintain their body temperature in cold conditions. This is now known as Bergmann’s Rule.
Body size affects everything from the ability to catch food to the chances of escaping from predators to finding a mate. Wildlife is already facing a wide range of threats like urbanization and fragmentation of landscapes — pushing certain species even closer to extinction. So, as animals get smaller in size, it will have a ripple effect throughout the ecosystem.
We have actually seen this in the fossil record as about 56 million years ago rapid global warming events were occurring. These events are similar to the greenhouse warming that we are currently experiencing. One of the changes that occurred during these events was the phenomenon of animals shrinking. These warming events accompanied with animals getting smaller caused massive extinction events from the land to the ocean. And actually was the largest deep-sea mass extinction event in the last 93 million years.
The temperature change that caused this extinction was a mere 9° Fahrenheit over a 20,000-year time period. According to NOAA in just the past 100 years our temperatures have changed by 2° Fahrenheit, which is a much more rapid pace than 56 million years ago which means wildlife barely has time to evolve to the changes.
Scientists are also finding that animals can only shrink so much until it becomes disadvantageous. A recent model of water requirements for smaller-bodied desert birds provided evidence that their small body size makes them more susceptible to dehydration on hot days. This means their size may help with cooling, but it causes trade-offs that could be deadly.
Discovering animals are shrinking sheds light on the far-reaching impacts of climate change and can help gain insight into their tolerances and better predict wildlife’s responses to future changes.