By Rebecca Morelle
Science reporter, BBC News
The tactics used by elephants to keep their cool in extreme desert heat have been caught on camera.
A BBC crew filmed the tusked beasts spraying themselves with water that they had stored in a reservoir in their throats several hours earlier.
Although this behaviour was first documented 100 years ago, the team believes this is the first time desert elephants have been filmed doing it.
The footage was recorded over six months in the Namib Desert, Namibia.
It forms part of Natural World's Elephant Nomads of the Namib Desert programme.
Cameraman Martyn Colbeck, who has spent the last two decades filming elephants, said: "Elephants normally drink every day, but the desert elephant has adapted to go up to five days without drinking.
"Just behind the tongue they have this little pouch called the pharyngeal pouch. This is an area that is used partly in communication - it allows the elephants to have all of the deep calls, but they can also store several litres of water in it.
"The desert elephants obviously regularly keep water in this pouch, but it is very rare to see them actually use it."
Elephants, old and young, sprayed themselves with stored water
Mr Colbeck was able to film the elephants take advantage of their water reservoirs as extreme temperatures hit the region.
He told the BBC News website: "Seven elephants left the main river system and went right up into the mountains to get to a plant that they like eating."
However, once the creatures had reached the top of the mountain, the temperature shot up to 45C (113F) and shade was extremely limited.
He said: "At midday, the elephants started to regurgitate the water that they had stored earlier that morning into the tips of their trunks.
"They sprayed it on to the outside of the ear that was facing the wind to cool down; they also sprayed it on to the inside of the ear where all the really thick veins lie to maximise the cooling effect.
"The bulls, the females and the calves were all doing it - this went on every 20 minutes for several hours - they must have had several litres stored," Mr Colbeck explained.
"This is a very unusual thing to see. Before this, I'd only seen it twice in 18 years - and this is the first time we have filmed it."
Elephant Nomads of the Namib Desert will be shown on BBC Two on Wednesday 26 March at 2000 GMT