As we enter the dog days of summer, people will try all sorts of things to escape the heat, from sweating in front of a fan to drinking a piping hot cup of tea (which actually does help). But body heat is about more than comfort—it's a question of survival. Rising body temperature puts more stress on various functions, for instance, increasing blood flow and putting strain on the heart and brain. With global temperatures consistently hitting record highs, how efficiently an animal can keep cool could spell the difference between existence and extinction.
When it comes to our natural method of regulating body temperature, humans are among the only animals in the world who cool down by perspiration. But our scaled, furred or feathered friends aren't left to suffer helplessly in the heat. Some creatures have evolved unique—and sometimes disgusting—adaptations to deal with scorching temperatures.
Sweating might be the most familiar way to cool down, mainly because it's the favored method of humans. Sweat is made mostly of water with some potassium, salt and other minerals. As it evaporates from the skin, it carries heat away and reduces your overall body temperature. Sweat is produced in sweat glands, which are activated by the hypothalamus, the area of your brain that controls certain key biological processes, including your heart rate, your blood pressure and your body temperature. The average human body has between two and five million sweat glands.
Humans aren't the only animals with sweat glands, but we are one of the few species that produces large amounts of perspiration to cool off. While sweating might lead to awkward encounters on a hot day, some scientists think that it also gave us an evolutionary advantage. Daniel Lieberman, professor of Human Evolutionary Biology at Harvard University, argues that our ability to sweat let us run longer distances at faster speeds than other animals. This meant humans could hunt game during the hottest parts of the day, when other predators were forced to rest. Other experts, such as anthropologist Nina Jablonski at Pennsylvania State University, say that sweating provided more efficient cooling that allowed us to evolve bigger, hotter brains.
In addition to higher primates (monkeys, apes and humans), horses are among the only other animals in the world that perspire profusely—making them one of the few that could challenge humans in a marathon.
Storks might be graceful birds, but their preferred method for cooling off is anything but. Several species of storks, as well as vultures, will defecate on their legs to cool down. Since bird poop is mostly liquid, it works the same way that sweating does, through evaporative cooling. As the poop dries on the birds' legs, heat is carried away, bringing down their body temperature.
Animals that don't sweat must find other means of cooling off. For pigs, hippos, boars and buffalo, nothing says "summer refreshment" quite like a roll in the mud. Similar to sweating, wallowing helps animals cool down via evaporation. As water from the mud evaporates from an animal's skin, it carries heat away and brings down body temperature, sometimes by as much as 3.6 degrees Fahrenheit. Why choose mud over a dip in clean water? It has nothing to do with a pig's penchant for dirt—water in mud evaporates more slowly than clear water, allowing the animals to feel cooler for longer.
While temperature regulation is the main motivation for wallowing, researchers have found that pigs will roll in the mud in cool weather too. It's possible cool pigs choose to wallow to remove parasites, or even just because of a behavioral preference. In a 2011 study, Marc Bracke at the Wageningen University and Research Center in the Netherlands suggested that the tendency to wallow evolved in pigs' ancient ancestors, and that pigs lack sweat glands because they wallow, as opposed to wallowing because they lack sweat glands.
The large ears of a jackrabbit (hare) might be adorable, but they're also functional: a large network of blood vessels running through the ears allows a hare to regulate body temperature as needed. If a hare is too cold, these blood vessels constrict to conserve body heat. If the outside temperature is above the hare's internal temperature, the blood vessels dilate, increasing their surface-area-to-volume ratio and encouraging heat loss. By regulating body temperature through their ears, the desert-dwelling hares are able to conserve water, because they don't lose moisture through sweating or panting.
Elephants also use their ears for temperature regulation. Elephants flap their ears like fans, helping cool the blood flowing through the vessels in their ears. Between the flapping and the thin skin, blood moving through the ears can cool by as much as 14 degrees Fahrenheit. To magnify the effect, elephants also will spray water on their ears.
In 2012, Stanford biologists H. Craig Heller and Dennis Grahn released a device that used similar methods to cool human skin. The cooling glove works by pulling blood vessels in the hands closer to the surface of the skin and then cooling them down via cold air circulating through the glove. The device, the researchers say, could be used to help ease muscle fatigue during exercise.
As warm-blooded creatures that lack sweat glands, birds have to find unique ways to regulate their body temperature. For those that don't want to resort to pooping on themselves, there's gular fluttering, or vibrating muscles and bones in the throat. Gular fluttering helps regulate temperature by increasing evaporation through the membranes in the throat—the more a bird vibrates them, the more the moist throat membranes are exposed to air, allowing for better evaporation. Because the process involves only a small amount of muscle and bone, it doesn't require a lot of energy, making it a fairly efficient mode of cooling. Types of birds that employ gular fluttering include pelicans, herons, doves, owls, quail and nighthawks.
When you think of an animal sleeping to escape the elements, you probably think of bears hibernating through frigid winter months. But there's a flip side, and it's called estivation, when animals "sleep" through scorching temperatures. Estivation helps animals survive by slowing their metabolism, which means they don't need to eat as much during hot months when vegetation and prey can be scarce. Some animals, like certain snails, estivate to prevent drying out by retreating back into their protective shells. Other animals, like the lungfish, will estivate underground, burrowing into the mud near water, where it remains dormant until the next wet season.
More mundane creatures also estivate. A 2013 study of common earthworms, for instance, found that the worms are capable of surviving in drought-ridden areas for weeks at a time thanks to estivation. That's good news for arid parts of the country, like eastern Colorado, which need earthworms to mix soils in dry, no-till areas of agricultural production.
Breath is hot, so when animals want to cool down, it's no surprise that they try to get their hot breath away from them as quickly as possible. Rapidly expelling hot air and drawing in cooler air is known as panting. When the cool air comes in contact with the moist lining of the lungs and throat, it helps the animal reduce its body temperature. You've definitely seen dogs do it—canines sweat through their paws but also pant to cool off more efficiently. But you might be surprised to know that pet pooches aren't the only ones taking advantage of panting's cooling properties: birds have been known to pant, as well.
Sometimes getting out of the sun is the best way for an animal to avoid overheating. Reptiles control their body heat via the environment, so if an area is too hot or sunny, they'll simply move to a shadier area to cool off. Conversely, if they want to warm up to boost their metabolism, they'll seek the sun. Because they don't use any type of internal regulation, reptiles spend less energy dealing with their temperature, meaning they need far less food than other animals. But their dependence on the outside world also leaves them extremely susceptible to environmental changes—even a cloud passing in front of the sun can affect small reptiles.
Sensitivity to the environment means that climate change poses a big problem for reptiles—some scientists estimate that 20 percent of lizard species could go extinct by 2080 if warming trends continue. Even if somehow we could completely halt global warming tomorrow, six percent of lizard species are still doomed to extinction thanks to the greenhouse gases currently present in our atmosphere. Mexico's blue spiny lizard, for example, has been forced to spend more time hiding from the sun rather than hunting or reproducing, something that's driving it to extinction.