What's the best wood for constructing beds? According to chimpanzees, one wood is superior to all others for beds: Ugandan ironwood.
And chimps should know. They make their own beds and sleep in them too, as the old saying goes. Each chimp is a bed builder.
They seem to be picky as well.
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"Chimpanzees, like humans, are highly selective when it comes to where they sleep," David Samson of the University of Nevada said in a press 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."
Samson and colleague Kevin Hunt of Indiana University studied chimps at the Toro-Semliki Wildlife Reserve in Uganda, which has seven tree species commonly used by chimpanzees.
Although the chimps had plenty of trees to choose from, a vast majority of the primates selected Ugandan ironwood to construct the 1844 chimp beds/nests documented by the researchers. "Ironwood" is a common name for a large number of woods that have a reputation for hardness.
Ugandan ironwood represented just 9.6 percent of all trees in the study area, showing that the chimps really took time and effort to seek it out. What's then so special about it?
For the study, published in PLOS ONE, Samson and Hunt measured the stiffness and bending strength of 326 branches from the seven common tree species.
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Ugandan ironwood was the stiffest and had the greatest bending strength of all the trees tested. It also had the smallest distance between leaves on the branches, and had the smallest leaf surface area.
In short, it produced a firm and stable "mattress" upon which the chimps could slumber. The authors further note that chimp beds constructed out of Ugandan ironwood may provide protection from predators and pathogens, as well as provide temperature regulation and comfort.
Worldwide, there are more than 100 species of trees and shrubs with the common name of ironwood, so it's possible that this type of wood, in general, is favored by all chimps that can get their hands on it.
Image: "Charles" (an adult male chimp) shown sitting in a C. alexandri tree; Credit: David Samson