Two species of flying squirrel living in the tropical rainforests of Hainan Island off China carve grooves around nuts so they can be wedged in the forks of twigs without falling out.
Suqin Fang at Sun Yat-Sen University in Guangzhou, China, says one one of these species may have learned the behaviour from watching the other, though this is hard to establish. If this did happen, it would be the first known example of an animal culture being transmitted between different species. “We think this is worth further study,” says Fang.
Some squirrels in the tropics hang clusters of nuts over tree branches rather than burying them in the ground, probably because buried nuts rapidly germinate or decompose in warm, wet conditions. Storing individual nuts in trees is much trickier because they typically have rounded shapes.
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Yet in 2005, when team member Han Xu of the Chinese Academy of Forestry went to study plants in the tropical rainforests on Hainan, he was intrigued to see nuts placed in the forks between twigs. The nuts stay in place even if the branches are shaken because the twigs fit into a groove chewed in a circle around the middle of the usually acorn-shaped nuts.
Other researchers have known about this for at least 40 years, Fang says, and local people for much longer. But after finding no scientific report about this behaviour, last year Xu, Fang and their colleagues decided to study and describe it.
The team found and documented around 150 stored nuts in a 5-hectare area of forest, in a wide variety of young trees and shrubs. The researchers say the squirrels’ carpentry works in a similar way to traditional Chinese mortise-and-tenon joints.
They then set up 32 infrared cameras to monitor some of the stored nuts. They found two species of squirrels came to check the nuts or retrieve them: a subspecies of the Hainan flying squirrel called Hylopetes phayrei electilis and the particoloured flying squirrel (Hylopetes alboniger).
The videos don’t show the initial carving and placement of the nuts. But while checking nuts, the animals sometimes refine the grooves to improve the fit, says Fang, so the team is confident they have found the animals responsible. Only once did the team record another species of squirrel stealing the nuts.
“There are nine different squirrel species living in Hainan Island, but only these two squirrel species have this behaviour,” says Fang.
The researchers think this nut carpentry is a learned behaviour, meaning it is an example of an animal culture that is passed from individual to individual. What’s more, the fact that two species in the same area do it implies that one species learned it from the other.
“I cannot think of a journal article reporting social learning from one species to another,” says at the University of St Andrews in the UK, who studies animal culture. “This may be just because it is indeed rare luck to record such a thing, rather than it never happening.”
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