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Chimps Prefer Nests Made of Ugandan Ironwood, New Study Says

According to the study by a group of biologists from the United States, chimpanzees (Pan Troglodytes) are intended to choose a certain type of wood when making their nests.


A male chimpanzee at the Toro-Semliki Wildlife Reserve, Uganda. Image credit: © Caroline Deimel, 2012.

It is the common practice for large-bodied hominoids to build their nest. As for chimpanzees, most of them prefer to choose certain kinds of tree species where they like to sleep more frequently. However, the reason why they would do it is unknown.

In order to find out whether the physical characteristics of trees would affect the selection behavior of nesting site, Dr David Samson from the University of Nevada and Dr Kevin Hunt from Indiana University had made measurement of the physical properties of wood from common tree species at Uganda’s Toro-Semliki Wildlife Reserve.

By doing so, they measured 326 branches from the seven tree species in regard to their stiffness and bending strength, because the chimps often selected such tree species for nesting location. In addition, they also measured leaf surface area to identify the unique structure or architecture of these seven species respectively.

From the study of 1,844 nests sampled, the scientists found that chimpanzees had chosen Ugandan ironwood (Cynometra alexandri) as their nests by 73.6 percent, although it accounted for just 9.6 percent of all trees in the area where the samples were collected.

Among all the trees tested, Ugandan ironwood (also called as Muhimbi in local dialect), was the stiffest tree with the greatest bending strength and the smallest distance between leaves on the branches, thus having the smallest leaf surface area.

Dr Samson and Dr Hunt said that the reason why chimpanzees chose the Ugandan ironwood or similar tress mainly depended on the properties of such trees, which might protect chimpanzees from predators and pathogens and also offer them temperature regulation and comfortable sleep they needed. .

Dr Samson, the first author of the article published in the journal PLoS ONE explained that as humans did, chimpanzees were fastidious in finding a place to sleep. It showed that the apes were naturally born to care more about a comfortable bed and they were even highly selective of wood they used to make it.

Journal reference:

Samson DR, Hunt KD. 2014. Chimpanzees Preferentially Select Sleeping Platform Construction Tree Species with Biomechanical Properties that Yield Stable, Firm, but Compliant Nests. PLoS ONE 9 (4): e95361; doi: 10.1371/journal.pone.0095361