Monday, March 17, 2014

Don't Sweat It: How elephants beat the heat

by Rebecca Shoer

A common question people ask us about elephants (aside from
"Do they ever stop eating?") is whether or not elephants sweat.  All three species of elephants (savannah, forest,
and Asian) live in hot and even tropical climates, ones in which humans
definitely sweat a lot.  This means that,
for humans at least, we need to drink extra water to stay hydrated; as the days
warm up here in Thailand, I find myself drinking two or three liters of water a
day.  But what about elephants?  They drink around two hundred liters of a water a day, and this is just on an average day!  Do they sweat to beat the heat?  And if they do, just how much more water do
they need to be drinking to stay hydrated?

Water is one of the most important limiting factors in an
elephant's environment.  This is because an
elephant will much more quickly deplete a water source than a food source, and
like most animals she can survive longer without food than water.  In fact, one of the main roles of an elephant
matriarch is to lead her herd annually from watering hole to watering hole.  If they arrive at a known watering hole and
find that it's dry, the elephants will dig in the soil to access the water
trapped below.  And they don't just use
this water for drinking: elephants use water to cool off, and mixed with dirt
they can cover themselves with a protective mud coat.  Of course, elephants also love the water for
fun and play: just watch this clip of Lamyai playing in the water in the grasslands!

Elephants need a lot of water, and they need it every day--the elephants here get two to three baths a day.  Because of this, it would be unreasonable and unfeasible for an elephant to sweat extra during the hot season--she would not be able to drink enough water to make up for the loss of moisture through her skin.  Perhaps, as elephant ancestors moved and their habitats warmed, individuals that sweat less survived and reproduced more than their sweatier cousins.  This process continued over centuries and millennia until the arrival of the modern Elephas maximus.  Now, even on a hot day, you will find that a toasty elephant doesn't have a sweaty brow to match your own.  In fact, there is only one place on an elephant's body that she can sweat from, and it's a tricky place to spot!  Looking at this picture, can you see her sweat?

Photo by Elise Gilchrist

If you guessed her toenails, you were right!  Elephants do possess sweat gland tissue equivalent to that of humans in the cuticles of their toe nails (Lamps et al. 2001).  Why did they retain these miniscule glands, if they most likely do little to cool them off?  Well, it all has to do with natural selection: so long as a trait isn't harmful, or doesn't reduce an individual's ability to reproduce, it will persist through the generations.  Even thousands of years from now, elephants may still have these small glands between their toes.

So if they can't sweat, how do elephants cool off?  Well, we already mentioned one method: a good dip in the pond and a nice mud pack can keep an elephant nice and cool.  They also use their amply-sized ears to keep cool: not only do they flap like giant fans, but the skin on their ears is so thin that the blood itself is cooled by this flapping motion.  Indeed, elephants' blood may be cooled anywhere from 2 to 8 degrees centigrade, which then circulates throughout the rest of their body. 

Picture by Rebecca Shoer

Finally, three recent studies have revealed previously undiscovered thermoregulation strategies of both Asian and African elephants.  First, Asian elephants have been shown to allow their internal body temperature to fluctuate significantly during hot days (Weissenbock et al., 2011).  This may sound like an odd strategy to keep cool, but the true benefit of this strategy becomes apparent over night: Asian elephants allow their body temperature to dip much lower than other animals, and this gives them a sort of internal shield against the heat during the day.  Second, the same research group found that African elephant have "thermal windows," or areas around their bodies where the skin is thin and there is a large concentration of blood vessels (Weissenbock et al., 2010).  These "windows" give the elephants even more areas from which to cool off their blood, and thus keep their body temperature cool.  Lastly, a third study found that elephants' sparse body hair is actually used to dissipate heat from their bodies (Myhrvold et al., 2012).  The hairs allow elephants to increase body heat loss (and thus decrease body temperature) up to 20%.  It may seem counterintuitive, but this is the first documented example of hair being used to cool off an animal instead of keeping it warm!

Nong Sam is extra hairy to help him cool off while he's growing. 
Picture by Rebecca Shoer

No matter how much we think we may know about elephants, they are still full of mystery, from their intelligence and behavior to even their most basic biology.  As the population of all elephants continues to decline, and with so few labs in the world researching these incredible individuals, we are in a race against time to try to discover the secrets of these spectacular species.

Lamps, L.W., Smoller, B.R., Rasmussen, L.E., Slade, B.E., Fritsch, G., Goodwin, T.E.. 2001. "Characterization of interdigital glands in the Asian elephant (Elephas maximus)." Research in Veterinary Science. 71(3):197-200.
Myhrvold, C.L., Stone, H.A., and Bou-Zeid, E. 2012. "What is the use of elephant hair?" PLoS ONE. 7(10)e47018.
Weisseböck, N. M., Arnold, W., and Ruf, T. 2011. "Taking the heat: thermoregulation in Asian elephants under different climatic conditions." Journal of Comparative Physiology. 182(2):311-9.

Weissenböck, N. M., Weiss, C. M., Schwammer, H. M., Kratochvill, H. 2010. "Thermal windows on the body surface of African elephants (Loxodonta africana) studied by infared thermography." Journal of Thermal Biology. 35(4):182-188.

1 comment:

  1. Please avoid all kind of elephant activity in Thailand, here is why;

    .. that includes any government supported protection centers, because it is a corrupt country.

    If you want to see elephant, the most human way would be to see them in wild, in many national parks across Thailand. Khao Yai, Kaeng Krachan and Kui Buri National Parks only few;