Award-winning journalist JEFF GOODELL has been at the forefront of environmental journalism for three decades. In his latest book Heat he examines the impact temperature rise will have on the future and how we can stop it. In this extract we discover the various strategies animals use to deal with heat.
To understand the power of heat, you have to think of it not just as a change in temperature, but as an evolutionary hurdle. Heat management is a survival tool for all life on Earth, and the strategies to deal with it are as diverse and colourful as the animal kingdom itself.
Elephants are particularly fascinating. They spend a lot of time in the sun. To cool off, they seek shade and water. (In Botswana, I once watched a young elephant frolic in a muddy watering hole on a hot day like a six-year-old kid at summer camp.) Their thin hair and flapping ears help with heat dissipation. More important, as temperatures rise, their hides become more permeable. Their skin effectively opens up, allowing them to perspire, even though they don’t actually have sweat glands.
Koalas hug trees with bark that is cooler than the air temperature. Kangaroos spit on their arms to wet them and cool off. Some squirrels use their bushy tails as parasols. Hippos roll in mud (water evaporates more slowly from mud, keeping them cool longer). Lions climb trees to get off the hot ground. Rabbits send blood to their big ears, using them as radiators. Vultures and storks defecate on their legs. Herons, nighthawks, pelicans, doves, and owls cool themselves with gular fluttering, a frequent vibration of their throat membranes, which increases airflow and thus increases evaporation. Giraffes’ beautifully patterned skin functions like a network of thermal windows. They direct warm blood to the vessels at the edges of the spots, forcing heat out of the animals’ bodies.
Other animals build structures to cool themselves, in some ways not so different from the way humans construct air-conditioned buildings. Termites build an elaborate system of air pockets within their mounds. Bees harvest water when they’re on their travels, then return to the hive and pass it by mouth to hive bees, which spread the droplets on the honeycomb. Other bees fan the water with their wings to cool the hive.
The silver Saharan ant, which thrives in a scorching environment in the Sahara and on the Arabian Peninsula, has evolved some remarkable heat-coping strategies. When a silver Saharan ant goes in search of food, it has 10 minutes before the desert heat will literally fry it. It ventures out in temperatures above 50 degrees, usually to scavenge the corpses of heat-killed animals. The ants go out only when it’s too hot for the lizards that prey on them but still cool enough that they don’t get cooked instantly. To avoid the superhot sand, they run fast – up to a metre per second, which, given their small body size, is the equivalent of a human running 725 kilometres per hour. The beautiful silver hue of the ant comes from unique triangular hairs on its body, which reflect away heat (just as wearing a white shirt keeps you cooler than wearing a black shirt).
To anyone who is used to riding a horse, camels are strange, calm, smelly, uncharismatic animals. The one I rode didn’t really seem to care much whether I was on him or not.
But you can’t talk about heat and animals without talking about camels. Not long ago, I spent a few days riding an Arabian camel across the Wadi Rum, a desert region in Jordan. To anyone who is used to riding a horse, camels are strange, calm, smelly, uncharismatic animals. The one I rode didn’t really seem to care much whether I was on him or not. My Jordanian guide said the camel did not have a name, and the guide did not seem to have much affection for him, which just made me feel sorry for the poor beast having to trudge across the desert with me on his back.
Camels evolved in North America roughly 40 million years ago, and their best-known features– their long eyelashes, their wide feet, their humps– may have come in response to North American winters. They crossed the land bridge at the Bering Strait about 14000 years ago, ending up on the Arabian Peninsula, among other places. They have been domesticated for thousands of years, nearly as long as horses.
Despite (or perhaps because of) their origins, camels are extremely well adapted to life in hot deserts. They have translucent eyelids that allow them to close their eyes and keep walking during sandstorms. They can also close their nose to keep sand out and water in. Thick tissue over a camel’s sternum allows it to easily raise its head above the hot ground when it is lying down. A camel’s hump shades and insulates internal organs from heat. Contrary to some myths, the hump doesn’t store water, it stores fat– which it can tap into when food is scarce. When a camel doesn’t eat for a long time, its hump sags.
For all living things, life in a hot climate requires careful water management, and camels are supremely good at it. They have unusual oval blood cells, which can circulate through thick blood, and quickly expand when water is available. During the winter and cold seasons, a camel can go without water for months. Under very hot conditions, it may drink only every eight to 10 days and lose up to a third of its body weight through dehydration. A dehydrated camel urinates only drops of concentrated urine, which look like white stripes on its hind legs and tail (it’s actually salt crystals). The way camels process their urine not only conserves water, but it also allows them to drink water that is even saltier than seawater, and to eat salty plants that would be toxic to most other animals. Their feces are so dry, they can fuel fires.
