Media playback is unsupported on your device Media caption Critically endangered chimpanzees in the Ivory Coast craft extra-absorbent drinking sticks, remote cameras reveal.

Researchers have used camera traps to film tool-use that is unique to chimpanzees in Ivory Coast.

The footage revealed that the clever primates habitually make special water-dipping sticks - chewing the end of the stick to turn it into a soft, water-absorbing brush.

Primate researchers examined the "dipping sticks" and concluded they were made specifically for drinking.

The findings are reported in the American Journal of Primatology.

Lead researcher Juan Lapuente, from the Comoe Chimpanzee Conservation Project, in Ivory Coast, explained that using similar brush-tipped sticks to dip into bees' nests for honey was common in chimpanzee populations across Africa.

"But the use of brush-tipped sticks to dip for water is completely new and had never been described before," he told BBC News.

"These chimps use especially long brush tips that they make specifically for water - much longer than those used for honey."

The researchers tested the chimps' drinking sticks in an "absorption experiment", which showed that the particularly long brush-tips provided an advantage.

"The longer the brush, the more water they collect," said Mr Lapuente.

"This technology allows Comoe chimpanzees to obtain water from extremely narrow and deep tree holes that only they - and no other animal - can exploit, which [gives] them a superb adaptive advantage to survive in this dry and unpredictable environment."

Image copyright Kathelijine Koops

This suggests that this particular population of chimpanzees has what the researchers call a "drinking culture" - a custom shared throughout this group of making these special water-dipping sticks to help them through the dry season.

The population belongs to the Western Chimpanzee sub-species, now critically endangered.

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