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Choosy Chimps Use Strongest Wood for a Nice, Firm Bed

Image: Ugandan chimp
Charles, an adult male chimp, is sitting in a Ugandan ironwood tree.David Samson / Univ. of Nevada

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Chimpanzees can be as choosy as humans when it comes to the beds they sleep in — and they prefer a firm, stable, resilient place to flop.

That's what researchers concluded in a paper published Wednesday in the open-access journal PLOS ONE, based on a survey of chimpanzee nests in Uganda's Toro-Semliki Wildlife Reserve. The bottom line? The sturdiest, leafiest lumber was by far the chimps' favorite bed-building material.

"Chimpanzees, like humans, are highly selective when it comes to where they sleep," the University of Nevada's David Samson said in a news release. "This suggests that for apes there is something inherently attractive about a comfortable bed — down to what kind of wood you use to make it."

Image: Ugandan chimp
Charles, an adult male chimp, is sitting in a Ugandan ironwood tree.David Samson / Univ. of Nevada

Samson and a colleague, Kevin Hunt of Indiana University, surveyed the types of wood used in 1,844 nests. They found that a species known as Ugandan ironwood (Cynometra alexandri) was selected for 73.6 percent of the nests, even though it accounted for only 9.6 percent of the trees in the sample area.

Then the researchers measured the stiffness and bending strength of 326 tree branches from the seven most commonly used species. Ugandan ironwood rated highest on both those scales. It also had the smallest distance between leaves on the branch, and the smallest leaf surface area.

Samson and Hunt suggest that chimps select ironwood branches because they provide the best protection from threats, pose the lowest risk of breaking and causing a fall — and are also leafy enough to be comfortable. So the next time it's bedtime for Bonzo, offer him Ugandan ironwood.

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