Chimpanzees 'choose beds with care'
Chimpanzees choose their beds with the same care and attention to comfort as their human cousins, research has shown.
Like many people perusing the showrooms of Habitat or John Lewis, they prefer a mattress that is springy and firm.
The apes build high sleeping platforms out of branches, but are fussy about what tree species they take them from.
Scientists found that the favourite bed material for chimps on the Toro-Semliki Wildlife Reserve in Uganda was Cynometra alexandri, known locally as "ironwood" because of its density and strength. Yet "ironwood" accounted for just 9.6% of trees in the area studied.
Of 1,844 chimp nests examined by the researchers on the 548 square kilometre reserve, 73.6% were constructed from C.alexandri.
Tests on 326 branches from seven tree species most often used to build chimpanzee beds showed that "ironwood" was the stiffest and had the greatest bending strength.
It was therefore ideal for comfortably supporting an ape weighing 30 kilogrammes or more.
C. alexandri also had the smallest leaf surface area, and the narrowest gaps between leaves on the branches.
Researcher Dr David Samson, from the University of Nevada in the US, said: "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."
Chimpanzees building nests weave together branches and foliage to create a thick springy "mattress" which can be anything from 10 to 150 feet off the ground.
Sleeping platforms provide protection from predators, and help to regulate temperature and keep biting insects at bay.
But another purpose is simply to allow a good night's sleep, scientists believe.
The researchers wrote in the online journal Public Library of Science ONE: "A compliant yet constraining structure reduces stress on tissues and the functional concavity of the nests obviates the need to adjust posture during sleep to prevent falls.
"This sleep quality hypothesis holds that apes construct sleeping platforms to allow uninterrupted sleep and to promote longer individual sleep stages, resulting in a higher sleep quality."
They concluded: "Chimpanzees are aware of the structural properties of C. alexandri branches and choose it because its properties afford chimpanzees sleeping platforms that are firm, stable and resilient."