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.
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.