Rainforest chimpanzees dig wells for cleaner water

A team of researchers led by the University of Kent has discovered that rainforest chimpanzees dig wells to reach cleaner water, and the idea is catching on. Such behavior is not common in the animal kingdom, and the few species that have been observed digging to access water are primarily in dry, hot regions. This is the first time the well-digging behavior has been observed in rainforest chimpanzees.

“Access to resources shapes species’ physiology and behavior. Water is not typically considered a limiting resource for rainforest-living chimpanzees; however, several savannah and savannah-woodland communities show behavioural adaptations to limited water,” wrote the study authors.  

“Here, we provide a first report of habitual well-digging in a rainforest-living group of East African chimpanzees (Pan troglodytes schweinfurthii) and suggest that it may have been imported into the community’s behavioural repertoire by an immigrant female.”

The study was focused on rainforest chimpanzees in the Waibira community of Uganda. A young immigrant female named Onyofi, who arrived in 2015, was the first to be seen digging a well. The experts say that she was immediately very proficient, which suggests that she perhaps grew up in a well-digging community.

In the days and weeks to follow, several other young Waibira chimpanzees and adult females were seen digging wells. While the adult males were seen using the wells dug by others, they were never seen digging them. 

“Well digging is usually done to access water in very dry habitats – in chimpanzees, we only know about three savannah living groups who do so,” said study lead author Hella Péter.

“What we’ve seen in Waibira is a bit different from those groups. First, they live in a rainforest, so most people assume getting water shouldn’t be a challenge – but it looks like the yearly few months of dry season is enough to cause some trouble for them!”

“What’s also interesting is that the wells all appear next to open water, so the purpose of them is likely filtering, not reaching the water – the chimpanzees might get cleaner or differently flavoured water from a well, which is fascinating.”

Onyofi was carefully watched both by young chimps and other adults as she dug. This indicates she was the first to bring this idea to the Waibira community. 

The researchers say that her wells seemed popular, with other chimpanzees drinking from them directly, or using chewed up leaves or moss, demonstrating that there seems to be some added benefit to well-water.

“One of the most interesting things was seeing the other chimpanzees’ responses to Onyofi’s digging – even large dominant males would politely wait for her to finish digging and drinking, and only then go and borrow her well, which is pretty unusual around such a valuable resource,” said study co-author Dr. Catherine Hobaiter.

“We’re curious to see what happens once some of the young males who can dig grow older – maybe they will be acceptable teachers for the big males, and they’ll stop relying on others to dig wells for them.”

The study is published in the journal Primates.

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By Chrissy Sexton, Earth.com Staff Writer