Chimpanzees looking for a good night's sleep prefer a particular kind of wood for a nighttime nest, seeking it out even though it comes from a tree not common in their habitat, researchers found.
U.S. researchers say chimpanzees in a study area preferred Ugandan ironwood branches for their nests because of its stable, resilient and firm qualities, and chose it over other available woods despite that fact Ugandan ironwood trees represented less than 10 percent of all trees present in the study area.
Examining 1,844 nests, researchers from Indiana University and the University of Nevada found 73.6 percent had been constructed of ironwood branches even though such trees were sparse in the area studies, the Toro-Semliki Wildlife Reserve in Uganda.
Of branches taken from seven species of trees most commonly utilized by the chimpanzees for their nests, Ugandan ironwood had the most bending strength and it branches were the stiffest of all trees examined, they say.
It also presented the least distance between separate leaves on each branch, and the densely configured leaves may provide insulation to keep a sleeping chimp warm, they say.
A chimp's bed must be both durable and secure so the chimps don't face the risk of falling out of them during the night, the researchers noted, possibly into the claws and teeth of a predator.
The strength of ironwood is likely why it's the chimps' first choice, researchers said.
"Despite the fact it's relatively rare, they're saying seven out of 10 times, 'I want to sleep in this species,'" University of Nevada, Las Vegas, anthropologist David Samson says.
"Chimpanzees, like humans, are highly selective when it comes to where they sleep," he says. "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."
Choosing the best nest-building material is particularly important for the chimps because they prefer to build a new nest in a different location each night rather than sleep twice in the same one, primatologists say.
There are a number of reasons chimps may have learned to prefer ironwood over other trees, including "stiffness, strength and leaf surface area, and that they select species that provide the widest range of advantages, including predator avoidance, postural stability, thermoregulation and pathogen avoidance," the authors wrote.
