Many news and scientific reports suggest that if the climate continues warming, it will spell the end for many animals. Life on our planet is tough. While some animals may not be able to adapt as fast as climates are warming, studies are finding that other animals may be able to compensate for increasing air temperatures. Whether you are an animal that can create internal body heat or not, the effects of a warmer body are the same. As an animal's body temperature increases, the chemical reactions inside its body also increase, dramatically speeding up its energy use. For example, a 10°C increase in body temperature generally makes energy use two to three times higher. However, several studies show that some animals, including a few birds, can suppress their metabolism to save energy and decrease the body heat they generate, helping them to avoid overheating. With this in mind, Jochen J. Voges, Marc T. Freeman and Andrew E. McKechnie from the University of Pretoria, South Africa, and Blair O. Wolf from the University of New Mexico, USA, wanted to know if only a few birds have this ability, or if more birds can suppress their metabolism to compensate for warming up.
To answer this question, Voges and colleagues took published and unpublished datasets of the resting metabolism of 30 small to large birds (9–430 g) from different environment types in South Africa, North America and Australia. Birds normally keep their metabolism and body temperatures relatively constant when they are sitting at a comfortable air temperature. But when many birds get too hot, they pant, much like a dog, allowing water to evaporate from their mouths, cooling them down. This panting also increases their metabolism and produces more body heat. To ensure they excluded panting, heat-stressed birds, the researchers only included metabolic measurements of birds with body temperatures ranging from 39 to 44°C. The team then used these data to calculate how much a bird's metabolic rate increases with rising body temperatures.
Voges and colleagues found that 29 out of the 30 bird species had lower metabolic rates than expected for how warm their bodies and the environment were. The team's findings suggest that birds decrease the body heat they generate by lowering their metabolism. And by generating less body heat, the birds will need to lose less water through evaporation to keep themselves cool, helping them avoid dehydration. The team points out that lowering metabolism would not only help birds stay cooler and more hydrated in hot, dry environments, but it would also help birds living in hot, humid environments. Because the air in hot, humid environments typically holds as much water as it can, meaning that water cannot evaporate from the birds when they pant. By reducing their metabolism, birds also reduce the body heat they generate, which keeps them from overheating. Although the scientists found that species varied in their ability to lower their metabolism, they suggest that reducing metabolism to avoid overheating and dehydration was likely passed down by the common ancestor of all birds.
With the flood of negative information about the potential impacts that climate warming will have on animal life, it can be hard to feel optimistic about the future. And the disappearance of many birds from their native ranges is alarming, to be sure. But this study by Voges and colleagues suggests that birds may have a few cards they can still play to stay in the game. Hopefully, their ability to lower their metabolic rate will help them to persist in a changing world.
