Elephants have hair on their heads to keep them cool: study

A team of scientists at Princeton University have found an answer: To keep them cool.

Unlike other animals whose hairy covering helps keep them warm in cold weather, the sparse hair of the elephant -- which tends to be found in hot climes -- helps carry heat away from the animal's skin and into the air, a study by Princeton University has found.

"Hair works as an insulator when it covers the skin," Elie Bou-Zeid, a professor of civil and environmental engineering who led the research team said.

"But in this paper, we show that sparse hair has the opposite effect. What was surprising to us when was the magnitude that we found for this positive effect," CNN quoted a Princeton news release as saying.

Elephants have the greatest need for heat loss of any modern terrestrial animal because of their high body-volume to skin-surface ratio, the report points out.

Many typical elephant behaviours help the giant creatures keep their cool -- from ear flapping to dust baths to water- spraying.

But none of this was quite enough to meet an adult elephant's need to release several kilowatts of heat every day, Bou-Zeid and lead author Conor Myhrvold said.

So they turned their attention to the little-noticed wiry hairs spaced out across the elephant's head or back -- and discovered they have a surprisingly significant effect.

In a slight breeze, the elephant's hair can enhance its ability to lose heat by up to 23 per cent, the team found.

The scientists considered the individual hairs, which vary in length and thickness depending where on the body they're found, as "pin fins," or slender protrusions that help to transfer heat.

Elephants have a maximum hair density of 1,500 hairs per square meter, compared with about 2 million hairs per square meter for the human head. The researchers calculated the average elephant to have a skin surface of 88 meters squared.

Asian elephants are notably hairier than their African cousins, the report says. Young elephants are also more hirsute than their elders.

"Elephant hair is the first documented example in nature where increasing heat transfer due to a low hair density covering may be a desirable effect," the team said.

"This elephant example dispels the widely-held assumption that in modern endotherms body hair functions exclusively as an insulator and could therefore be a first step to resolving the prior paradox of why hair was able to evolve in a world much warmer than our own."

The findings were published in the academic journal PLOS.