In April 2015, a TV crew was filming at the Royal Burgers Zoo in the Netherlands. It was the intention to film chimps in the enclosure from close-by and from above with the means of an aerial drone. When the drone came a bit closer to the primates, a female chimpanzee named Tushi made two sweeps with a branch that she held in a hand; the second one was successful and downed the drone. Now, in a paper published in the journal Primates, two researchers from the zoo explain the event as yet another example of chimps’ make-do attitude to using whatever is on hand as tools, and sometimes as weapons.
Tushi used a stick to attack the drone; behind her Raimee is also sitting with a long stick. Image credit: Jan A. R. A. M. van Hooff / Bas Lukkenaar.
“A trial run was made without recordings being made,” the authors, Jan van Hooff and Bas Lukkenaar of the Royal Burgers Zoo, said about the incident. “When the drone took off from the ground and made some maneuvers near and over the area, its visual appearance and humming noise caused some excitement initially. At this stage all chimpanzees were still on the ground.”
“Then a flight was made with the camera live. This flight started from outside the enclosure to make a survey shot of the area. The camera drone slowly entered the airspace above the apes at a height of 33 to 50 feet (10 – 15 m). By this time the chimpanzees were quiet again.”
The operator then closed in on two chimps that had settled at a height of about 16 feet (5 m) on the side of the scaffolding where the drone was and had been.
These were Tushi, born in 1992, and the female Raimee, born in 1999.
“Tushi moved towards the end of a beam in the direction of the hovering drone. The operator of the drone had clearly underestimated the significance of the fact that both individuals had carried with them a long twig when they climbed the scaffolding. This is not a frequently observed behavior of these chimpanzees,” the researchers said.
“When the drone came close, Tushi made two long sweeps with her branch, which she held in her left hand. The second one was successful and brought the drone down. The drone was broken, but the camera continued filming.”
The stick that was used to hit the drone was a willow twig of about 6 feet (1.8 m) in length. There are often willow twigs lying around. These are remnants of willow branches that have been given to the chimpanzees as a feeding pastime.
van Hooff commented: “the use of the stick as a weapon in this context was a unique action. It seemed deliberate, given the decision to collect it and carry it to a place where the drone might be attacked.”
“This episode adds to the indications that chimpanzees engage in forward planning of tool-use acts,” added Lukkenaar.
“This incident also shows the apes cautiously inspecting the contraption and even throwing it around before they lose interest in it.”
The chimps at the Royal Burgers Zoo have never explicitly been taught how to use different tools, according to the team, but they have had ample chance to watch humans handle all kinds of implements.
Previous studies showed that the chimps spontaneously and innovatively use up to 13 types of tools in a variety of ways, especially utilizing sticks of different sizes. They appear to choose the size, shape and weight of the tools with a particular use in mind.
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Jan A. R. A. M. van Hooff & Bas Lukkenaar. Captive chimpanzee takes down a drone: tool use toward a flying object. Primates, published online September 3, 2015; doi: 10.1007/s10329-015-0482-2
