New research shows that like humans, chimpanzees also worry about comfort and safety when they sleep. Scientists have found that chimpanzees often choose trees that offer safety, stability and comfort when making beds.

The study was conducted by researchers David Samson and Kevin Hunt from the University of Nevada and the Indiana University respectively. The pair found that chimpanzees often choose Ugandan ironwood trees when looking for a good place to sleep. Compared to other types of wood, Ugandan Ironwood offers firmness, stability and durability, which makes it a good choice for making beds. The researchers published their findings in the online journal PLOS ONE.

"Juvenile and adult apes devote considerable time and energy to the construction of a new sleeping platform or "nest" at the end of their daily active period," said Samson and Hunt. "Current data suggests that infants and young juveniles (i.e. nursing young) acquire skills over years both through observation of their mother and practice and begin making their own nests after weaning."

The researchers studied chimpanzees living in the Toro-Semliki Wildlife Reserve in Uganda. After studying the choices the chimps made to create 1,844 nests, the scientists found that 73.6 percent of the time, the chimps would choose Ugandan ironwood. The fact that this type of tree only made up around 9.6 percent of the trees in the area rules out simple convenience. The relative scarcity of Ugandan ironwood in the area supports the researchers' theory that the chimps chose this type of wood due to specific reasons.

"Chimpanzees, like humans, are highly selective when it comes to where they sleep. 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," added Samson.

Samson and Hunt also gathered data about the strength, capacity to bend and stiffness of 326 tree branches that came from seven of the chimps' favorite tree species. They found that Ugandan ironwood performed admirably in terms of bending strength and stiffness. Moreover, the fact that Ugandan ironwood branches also had very little distance between each leaf may have added to the wood's appeal for chimp bed making.

The researchers concluded that using ironwood branches afforded the chimps the best protection from potential dangers when they sleep. Moreover, using this type of wood also minimized the risk of the nest breaking apart while a chimpanzee was sleeping. Chimpanzees may also find that the amount of leaves in ironwood branches made for relatively comfortable beds.

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