How Trees Help Animals Keep Their Cool

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June 09, 2015 | 7,009 views

Story at-a-glance

  • Tree trunks can be more than 40 degrees Fahrenheit cooler than the air around them
  • Koalas hug trees to help cool their bodies down; they even have thinner fur on their bellies for this purpose
  • Leopards, primates, bats, squirrels, and reptiles may also “hug” trees to help regulate body temperature

By Dr. Becker

One of the ways your body keeps cool is by sweating, but fur-covered animals can’t sweat the way you do. Instead, they have other methods of keeping cool when the temperatures rise. Panting is one of the most well-known.

When your dog pants, he may take more than 300 breaths a minute. This rapid inhalation of cool air, coupled with exhalation of hot air, helps lower his body temperature (dogs also sweat through their paws).1,2

Many animals have an even more unique way of staying cool, one that you may not have heard before: hugging trees!

Why Animals Hug Trees to Stay Cool

Tree trunks can be more than 40 degrees Fahrenheit cooler than the air around them. When researchers observed 30 koalas during a spell of hot weather in Australia, they were often found hugging trees. This is not only characteristic of koalas, it also serves an important purpose in helping them cool off.

During extreme heat waves, up to one-quarter of certain koala populations have died. Having access to trees could make a major difference in the animals’ ability to survive during extreme heat.3 Lead researcher Dr. Natalie Briscoe, from the University of Melbourne, told Science Daily:4

Access to these trees can save about half the water a koala would need to keep cool on a hot day… Access to cool tree trunks would significantly reduce the amount of heat stress for koalas.”

In fact, when the researchers took heat imagery of the koalas, they were able to see their body temperatures respond to the cooling trees. The animals even have thinner fur on their bellies, which the researchers believe helps them maintain close contact with the tree trunk. Zoologist Michael Kearney of the University of Melbourne told Discovery News:5

“The blood flowing through the body would continually replenish cooled blood near the parts of the koala in contact with the tree with warm blood from other parts of the body, with the ultimate effect of cooling the whole body down."

Other Animals Hug Trees to Stay Cool Too

Koalas are not the only animals that “hug” trees to stay cool, either. Leopards, primates, bats, and, possibly, squirrels are known to do so, and even your house cat may lounge on a tree branch to cool off (if he’s allowed outdoors).

Cold-blooded animals, such as reptiles, also hug trees to help regulate their body temperature, and they may even be able to gather warmth from trees on cold days, although this hasn’t yet been confirmed.

Interestingly, animals will seek out specific trees to hug, as some are cooler than others. The researchers found Acacia trees to be the coolest, and it turns out these trees are favorites of koalas and other animals. Kearney continued:6

“Trees with smooth bark seem preferable because they have what's called a 'high thermal conductivity,' which means heat flows faster into or out of the object. Also, larger trees with thicker trunks are cooler.”

If you’re wondering why trees are so cool, researchers aren’t entirely sure, but it could be because they draw up cool ground water and also because they’re slow to change temperature in response to the surrounding temperature. Unfortunately, deforestation is taking away this vital habitat for many species. Kearney explained:

The availability of cooler trees should be considered when assessing habitat suitability under current and future climate scenarios.7

…How climate impacts organisms depends not only on their physiology, but also whether they can buffer themselves against climate variability via their behavior. One of the ways species can withstand hot temperatures is by seeking out cool microclimates, but only if their habitat provides such refuge.”8

Six Other Unique Ways Animals Stay Cool

We’ve covered panting and tree hugging, but there are quite a few other methods that animals use to beat the heat as well. Among them:9

  1. Sweating: Humans aren’t the only animals that sweat to stay cool. Primates, including monkeys and apes sweat, as do horses, who may perspire so profusely they start to “froth” or “foam.”
  2. Pooping: Some stork species, along with vultures, will poop on their legs to cool off. Remember, bird poop is mostly liquid, so it acts similar to sweating’s “evaporative cooling.” As the poop dries on their legs, it helps take body heat away.
  3. Rolling in mud: Pigs, hippos, boars, and buffalo love to roll in the mud to cool off. The mud sticks to their skin, and as the water it contains evaporates it carries heat away, helping to bring down body temperature. Pigs are unique in that they roll in mud even on cooler days, perhaps to remove parasites or simply because they like to.
  4. Blood vessels in the ears: Jackrabbits’ large ears help regulate body temperature by constricting or dilating blood vessels. The blood vessels will dilate on a hot day, which helps with heat loss. Elephants also use their ears to help cool off by flapping them like fans. This helps cool the blood flowing through the ears, which can lower body temperature significantly.
  5. Throat vibrations: Birds, including pelicans, herons, doves, owls, quail, and nighthawks, vibrate the muscles and bones in their throat, a process called gular fluttering. The vibrations expose the throat membranes to air, helping with evaporation and cooling.
  6. Estivation: Estivation is similar to hibernation, except the animals slow their metabolism and “sleep” through hot months. Certain snails, lungfish, and earthworms all use some form of estivation to survive extreme heat and droughts.

[+]Sources and References [-]Sources and References

  • 1, 9 Smithsonian.com August 7, 2014
  • 2 Paw Nation July 2, 2013
  • 3, 8 Biology Letters June 2014; 10(6)
  • 4, 7 Science Daily June 14, 2014
  • 5, 6 Discovery News June 3, 2014