GETTING an elephant to swallow a large metal pill is no easy task. 鈥淭hey are very intelligent animals and will check the food you prepare for them,鈥� says Nicole Weissenb枚ck.
Even hiding the 3-centimetre-long capsules in bananas 鈥� an elephant favourite 鈥� doesn鈥檛 work. 鈥淚f they bite on them, they don鈥檛 even crush them, they spit them back out,鈥� Weissenb枚ck says. Instead, she discovered, the trick is to wait until their mouths are open and then chuck the pills down their throats along with some tasty treats.
The metal pills contain not medicine but temperature sensors and radio transmitters. For big animals, staying cool is a challenge 鈥� and yet elephants, the largest land animals in the world, live in some of the hottest places. So how do they survive the heat? Weissenb枚ck and others have decided to find out, and they鈥檝e discovered that elephants have evolved some surprisingly sophisticated tricks.
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Large, warm-blooded animals not only generate a lot of internal heat, they have a smaller surface area relative to their volume. To maintain their body temperature when it鈥檚 hot, then, an elephant has to lose far more heat per unit of surface area than a person. The bigger the elephant, the bigger the problem. What鈥檚 more, elephants don鈥檛 sweat. They don鈥檛 pant either, probably because it doesn鈥檛 work well for such a huge animal.
Instead, of course, elephants have their huge ears, which act as radiators. They鈥檙e pretty effective: calculated that at a temperature of 20 掳C, a 2000-kilogram African elephant could shed all its excess heat through its ears alone. But African elephants can weigh up to 7000 kg and have to survive temperatures that can soar above 40 掳C. The ears of Asian elephants, meanwhile, are just a third of the size of African elephants, so they can only lose a third as much heat through them. Clearly, ears are not enough.
We鈥檝e known about some of their other strategies for a while. One is to flap their ears, to increase heat loss. Another is to head to the nearest pool. Not only does water provide , but , providing a lasting cooling effect as it slowly evaporates.
Thermal windows
When Weissenb枚ck, who is at the , Vienna, in Austria, took thermal images of six African elephants at Vienna Zoo, her team discovered another trick. They were expecting to see the ears show up as hot patches as the elephants shed heat, but they found many other hot patches on the animals鈥� bodies, including on their legs and flanks. Only elephants鈥� ears were thought to have the dense networks of blood vessels required to heat up the skin to this extent, but it now appears many other areas are just as well equipped ().
What鈥檚 more, elephants seem to have an astonishing degree of temperature control. As it got warmer, the team had expected to see the whole of each ear heat up. Instead, only small patches warmed at first, and the pattern varied from ear to ear. The temperature differences between the hot and cold patches were vast 鈥� as high as 20 掳C. 鈥淚t鈥檚 really quite amazing,鈥� says Weissenb枚ck.
As the temperature rose higher still, the hot areas expanded and eventually merged. All mammals have skin areas that can act as 鈥渢hermal windows鈥� through which heat escapes, but elephants are the first animals known to open, close and merge their windows in this way.
Weissenb枚ck thinks this ability allows elephants to fine-tune their body temperature in moderate weather. 鈥淭hey are only used when the elephant is comfortable 鈥� he is not freezing and he doesn鈥檛 feel too hot,鈥� she says. Other researchers have speculated that elephants can even cool specific organs depending on which skin patches heat up.
Heat flow from these patches is increased in another, unexpected way: by hair. While elephants appear to be bald, they are in fact covered in sparse hairs. 鈥淭hey鈥檙e bristly and wiry, and very thick,鈥� says .
Thick hair keeps mammals warm by trapping a layer of insulating air next to the skin, reducing heat loss. But elephant hair is too sparse for that. Instead, Myhrvold wondered if the hairs could act as tiny heat fins, increasing heat loss. While he was an undergraduate at Princeton University, he began investigating this effect by tweaking a computer model normally used to calculate the effectiveness of the heat exchangers used for cooling electrical components. The altered model suggests that elephants鈥� hairs can boost heat loss from skin by up to 20 per cent ().
鈥淲e are finding out a lot of surprising things about these animals,鈥� says Myhrvold. His work suggests that hair is not just a relic of their past, but may have evolved to help keep elephants cool. In fact, perhaps hair originally evolved for cooling rather than warming, he speculates.
鈥淭heir sparse hair boosts heat loss by up to a fifth. In fact, perhaps hair originally evolved for cooling, not warming鈥�
But even this host of tricks for shedding heat is not enough in extreme conditions. Then, elephants resort to a radical strategy. This is where the pill-like temperature sensors come in. Weissenb枚ck鈥檚 team managed to get 17 Asian elephants at zoos in Germany and Thailand to swallow the capsules. It鈥檚 the only way to monitor an elephant鈥檚 core temperature, says Weissenb枚ck. 鈥淵ou can鈥檛 really use rectal measures,鈥� she says. 鈥淵ou鈥檇 have to go one and a half metres inside the elephant to get the core body temperature.鈥�
In Germany, where the ambient temperature was around 21 掳C, the elephants鈥� core temperature varied by around half a degree over the course of a day. But in Thailand, where the temperature was around 30 掳C, they varied by more than 1 degree (see graph). From a minimum of 35.5 掳C at night, the elephants鈥� core temperature rose as high as 38 掳C during the day ().
So the elephants in Thailand are turning size to their advantage. Large bodies are not only hard to cool, they also take time to warm up. By letting their body temperature drop abnormally low during the night, the elephants can endure higher temperatures during the day without getting dangerously hot. A few other animals do this too 鈥� a camel鈥檚 temperature can range from 34 掳C to over 41 掳C 鈥� but the strategy was thought to be the preserve of desert mammals.
Weissenb枚ck thinks African elephants must also adopt this trick to stay cool, but no one has yet monitored core temperatures in African elephants exposed to extreme heat. Other large animals, such as rhinoceroses and , may well do the same.
What is clear is that as the planet warms, staying cool is going to become an ever bigger challenge for large animals. With night-time temperatures rising even faster than daytime ones in many regions, even the strategy of chilling down at night to survive hot days might not be enough. Some parts of elephants鈥� current ranges could become too hot for them to survive. 鈥淚t is pretty obvious that elephants are going to have to change their behaviour,鈥� says Myhrvold. They may change physically, too. Perhaps elephants will be forced to resort to the most radical strategy of all for a large animal: shrinking.
This article appeared in print under the headline 鈥淛ust chilling鈥�
