Eavesdropping on a well-cared-for group of chimpanzees in captivity finds they use a mixture of passionate gestures, vocalizations and even sign language to get their points across with each other, and also later with humans.
Like a passionate Italian using a combination of hand movements and sounds, the chimpanzees often succeed in conveying what's on their minds, which -- in the case of chimps -- is often food, playtime and an annoyance over being ignored.
The gestures frequently happen in sequences, according to the study, which is published in the journal Animal Cognition. Co-author Mary Lee Abshire Jensvold explained how one of the studied chimps, a male named Dar, playfully forced another male, Loulis, to pay attention:
"Dar open palm slapped, a tactile gesture, on Loulis. Loulis didn't respond. Dar then used a different gesture, the foot stomp, an auditory gesture, which makes noise. Loulis responded to that gesture. This shows a persistence in communication."
Jensvold, associate director of the Chimpanzee and Human Communication Institute, and her colleagues Maureen McCarthy and Deborah Fouts studied these two chimps along with three females -- Washoe, Moja and Tatu -- at the institute. The researchers say that four of "the chimpanzees were raised in an environment like that of a deaf human child and acquired signs of ASL (American Sign Language) in this environment." When he was brought into the group, the fifth chimp, Loulis, acquired many of the language signs by copying what the other primates were doing.
When the researchers studied how the chimps communicated with each other, they noticed that sign language was worked into the mix of chimp vocalizations and gestures.
"For example, they would sign CHASE in an interaction that is a request to be followed in a game," Jensvold said.
The chimpanzees also used their own unique mix of gestures not learned or somehow derived from humans. These included moves akin to high fives, fist bumps, feet claps, head nodding or moving side-to-side, arm flails, hugs, proud swaggers and pursed lip kissing.
"There is tremendous overlap in human and chimpanzee gestures," Jensvold shared. "Many gestures that you see in chimpanzee play, such as slaps, tickles, pokes, blocks and kicks, are ones that you would see in human play. Imagine play wrestling between two humans, and you've imagined a scene with two chimpanzees playing."
In terms of chimp sounds to accompany these moves, Jensvold explained that "the vocalizations were primarily food barks, laughter, and other vocalizations that augment the context."
"Other research from our lab shows that the chimpanzees will use a mouth sound," she said, "such as a raspberry sound, to get a caregiver's attention. Then the chimpanzees begin gesturing."
The findings show that chimps adjust their communications based on how much the intended receiver is paying attention. If that individual is looking at the chimp, the chimp likely will vocalize and gesture. If the individual isn't looking, he or she probably soon will, due to moves like gentle poking and annoyed foot stomps designed to grab attention.
"Dr. Jensvold's paper is a fantastic dataset from a very unique group of chimpanzees," Catherine Hobaiter of the University of St. Andrews School of Psychology and Neuroscience told Discovery News. "It is the first time that the natural gestures that all apes share have been researched in cross-fostered apes (meaning raised in a human environment) who also employ ASL signs."
Hobaiter added, "Given their unusual rearing history, it's really very interesting to see that much of their naturalistic gesturing follows similar patterns to those that we see working in the wild with free-living chimpanzees."
Hobaiter theorizes that some long gesture sequences evolved in chimpanzees to help regulate play. "For example," she said, "they may want to speed it up, slow it down or start to wrestle or chase."