How a chimp goes mattress hunting

Chimpanzees can’t go to a mattress store when they need a bed. They have to create one each night from tree branches.

Francesco Veronesi/Flickr (CC BY-NC-SA 2.0)

Note: The following scene is fiction (probably). Stay tuned for the real story below.

Two chimps, a mother and daughter, are touring a mattress store. They’re looking for beds to sleep in for the night. Actually, they’re looking for materials to make their beds — or nests, as they’re properly called. This is something chimps do every night for their entire lives after they’re weaned.

“What characteristics are you looking for in your bed?” asks the salesman. “Firm? Soft? Perhaps something that will protect you from biting insects? That will determine which trees are best for building your nests.”

“Well,” starts mom, “this is daughter’s first night building a nest of her own. Why don’t you explain our options.”

“If a good night’s sleep is what you want, then you should choose something with smaller leaves, a denser canopy and branchings shaped like a tripod,” the salesman explains. “Thermoregulation, though, will need a dense, leafier canopy. If you’re looking to avoid predators, you’ll want a tall tree with a broad canopy. But you should probably head over to one of the shops near a waterway or gorge, so you can use a slope to get even higher up. And if mosquitoes and the diseases they carry are your biggest worries, then you should consider trees that have compounds in the leaves, bark or sap that can keep those insects at bay.”

“All of those things sound good, mama,” daughter says. “How can I get all of them?”

“‘All’ might be asking for a bit much, but you should give ironwood a try,” the salesman recommends. “It’s what most of your fellow chimps use here in the Toro-Semliki Wildlife Reserve — that’s what the humans call our area of Uganda. Nearly three-quarters of our nests use branches from those trees. They’ll give you a firm bed with good insulation. And they might even repel insects. But they can be hard to find, since they make up less than 10 percent of the forest.”

“I’ve also used branches from oil palm trees,” mom says.

“Yes, those are among our biggest sellers here in Toro-Semliki,” the saleman says. “They’ll give you an entirely different nest. They’ve got large leaves and thorny stems. But these branches should help to keep predators away and might make communication between members of your group easier.”

“So, what do you think, daughter?” mom asks. “Which should we choose for your first nest?”

“Um, well, maybe ironwood?” daughter says tentatively.

“Excellent choice,” says the salesman. “Can’t go wrong with ironwood.”

“Yes, we’ll take the ironwood,” says mom. “And, daughter, we’ll practice your basketweave technique when we get back to our group.”

“Aw, mom, do I have to?”

The study

One of the more unusual traits apes share is that we sleep on beds. For apes other than humans, this means building a sleeping platform or nest every night. Young apes learn these skills from their moms and start making their own nests after they’re weaned. To make these thick and springy mattresses, the animals bend and break stiff, strong branches and interweave them.

David R. Samson of the University of Nevada, Las Vegas and Kevin D. Hunt of Indiana University in Bloomington surveyed 1,844 chimpanzee nests in Uganda’s Toro-Semliki Wildlife Reserve to find out what trees the animals were using to make their nests. They also surveyed the forest to see which species of trees were most abundant. And they measured the tree branches for properties such as strength and leaf surface area. The results of their study were published April 16 in PLOS ONE.

Of the nests investigated, 73.6 percent were made with ironwood, a species that made up only 9.6 percent of trees in the researchers’ forest transects. Ironwood was the stiffest and most stress-resistant of all the tree species tested.

“Chimpanzees select species of trees that possess physical properties that result in nests that are sturdy and resilient, optimizing comfort and reducing the risk of falls,” the researchers write.

The ironwood also probably provides a good deal of comfort, as its branches have a great density of small leaves. The thicker foliage also provides insulation. And the tree may indeed have insect-repellent properties, the researchers write.

The chimps learn to favor these particular trees — and the basketweave technique — by watching their moms. No annoying mattress salesmen, confusing fliers or annoying store jingles required.

Sarah Zielinski

Sarah Zielinski is managing editor of Science News for Students. She has a B.A. in biology from Cornell University and an M.A. in journalism from New York University. She writes about ecology, plants and animals.

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