Mother gorillas use a type of baby talk when communicating with infants, according to scientists.
The team studied captive western lowland gorillas, watching and filming the animals as they interacted.
These animals have a wide repertoire of communication gestures, so the team focused on facial expressions and hand signals used in play.
They published their findings in the American journal of Primatology.
Eva Maria Luef from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, led the research.
She and her colleague Katja Liebal filmed 120 hours of footage of the gorillas at Leipzig Zoo and Howletts and Port Lympne Wild Animal Parks in the UK.
Analysing this footage revealed that, when they played with infants, adult females used more tactile gestures than they used with other adults; they would touch, stroke and lightly slap the youngsters.
The infants also received more repetition, explained Dr Luef.
She described one particularly motherly gesture which the researchers call hand-on.
This is where mothers put the flat hand of their hand on top of the [infant's] head, said Dr Luef. It means 'stop it.'
Gorillas often use this gesture with one another; it is a signal that appears to mean that an animal has had enough. But with an infant, the female would repeat the action several times.
The researchers describe this motherly communication as non-vocal motherese.
They say that it helps infants to build the repertoire of signals they will use as adults, in order to communicate with the rest of the gorilla group.
It also shows that older animals possess a certain awareness of the infants' immature communication skills, said Dr Luef.
Learning to talk
Prof Richard Byrne from the University of St Andrews said that he doubted the research shed any light on the evolution of human babytalk.
The researcher explained the importance of the way in which adults talk to babies, describing it as a natural but very smart way of conveying the details of how we construct complex grammar.
But he added that, since gorillas do not acquire language, they have no need of such an adaptation.
So I suspect this is not the same at all, he said.
[But] it is interesting that the adults gesture in a different way to babies than among each other.
This suggest that adults understand that communicating to infants is going to be tricky, and plan their gesturing accordingly.
