The chimps' ability, documented in the latest issue of the journal Primates, demonstrates that these animals can learn without trial and error, since one mistake for them could be fatal.
The discovery also explains why wild chimpanzees living in Bossou, Guinea, suffer from very few snare-related injuries and deaths versus chimps living in other places.
"At Bossou, hunters are trying to catch cane rats," co-author Gaku Ohashi told Discovery News. "Sometimes duikers (a type of antelope) are trapped. Villagers at Bossou do not eat chimpanzees because they think of chimps as the reincarnation of their ancestors. However the snares cause indiscriminate damage, ensnaring any and all animals that come into contact with them."
Ohashi, a research fellow at the Japan Monkey Center, and colleague Tetsuro Matsuzawa observed the Bossou chimpanzees from July 2002 to March 2003 and then again from April to Sept. 2004. During those times, the researchers recorded six instances where five different wild male chimps took steps to deactivate snares they encountered.
One adult male chimp heard a female chimp, accompanied by her one-year-old infant, whimpering next to a duiker carcass in a snare. According to the researchers, the male chimp slapped the duiker, grimaced and then jumped away. He then grasped the snare with his hands and vigorously shook it. This same male had previously shaken another snare, causing it to break.
On another day, this male was with a few other adult chimps and a six-year-old juvenile male. When the group encountered a snare, the juvenile managed to completely deactivate the snare by causing ropes attached to it to become untied.
These, and the other documented instances, suggest the snare deactivation techniques may "have been passed down through the generations and carried on in the group as culture," Ohashi and Matsuzawa wrote.
"Some time in the past, an individual that had been ensnared might have started this behavior," explained Ohashi, who added that "young chimpanzees acquired this technique without any injuries."
In other locations, chimpanzees that survive snare injuries can be maimed for life. In Kalinzu Forest, Uganda, for example, 10 out of 16 identified males had injuries on their limbs. In Budongo Forest, also in Uganda, one-fifth of all chimps exhibited limb deformities due to snares.
Vernon Reynolds, a primate expert who serves as an adviser at the Budongo Forest Research Project, told Discovery News that the observations made at Bossou are "exceptional, not having been reported from any other site."
Reynolds isn't sure why the male chimpanzees at Bossou have the ability to deactivate snares, while chimps elsewhere do not. Wild chimpanzees in Africa, however, seem to often exhibit concern over the devices.
"Our chimps at Budongo make alarm calls at snares and also, on one occasion at least, our alpha male removed a snare from an adult female," Reynolds said.
Ohashi hopes better education at locations where the snares are used -- parts of East and West Africa -- could make hunters more aware of the unintended consequences of their actions. At Bossou, a local nongovernmental organization has also started farming cane rats in the village.
"If farming cane rats provides adequate subsistence for local people at Bossou," Ohashi and Matsuzawa conclude, "then snare hunting activity for bush meat may become less necessary and the risks facing chimpanzees should subsequently diminish."
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