Listen to gorillas 'sing' for their supper: Male apes produce tuneful calls and 'hum' while they eat their favourite plants, flowers and seeds
- The behaviour was seen in two groups of western lowland gorillas
- Adult male gorillas sung and hummed far more than females and juveniles
- Scientists believe the males may be directing the meal with their song
- It could also be a sign of contentment when eating food they like
They are the biggest primates on the planet, yet despite their imposing strength and size, gorillas can often display surprising moments of tenderness.
Now new research has revealed the male giant apes, well known for their booming chest beating roars, have another gentler side to them – they like to sing.
Biologists have found wild western lowland gorillas producing tuneful calls and deep hums while eating various different food types, perhaps as a sign of contentment.
Scroll down to hear the calls
Adult male western lowland gorillas have been found to sing and hum when they are eating (pictured). The males produced the distinctive calls more often than females in their group and seemed to do so only as they ate. Researchers believe the singing could form part of group cohesion during meal times
Adult males, including the dominant silverbacks, sing far more than females or juveniles, producing deep vibrating calls, making them the tenors of the forest.
The scientists who observed the behaviour said the animals only sing when eating.
The gorillas tended to sing most when they were enjoying aquatic plants, flowers and seeds, which are considered to be favourite foods.
Insects such as ants accounted for the least singing.
The researchers added that the songs are surprisingly quiet for such large animals, suggesting they are not used to alert other members of a group about the discovery of a food.
GORILLAS SEEN USING TOOLS
Anyone who has seen footage of gorillas in the wild will be struck by how hauntingly human-like their movements and behaviour can be.
But for the first time the great apes have been seen using tools, something that was believed to have separated them from our own species.
Last year scientists reported seeing a mountain gorilla in Rwanda using a stick to capture and then eat ants.
Previously the behaviour had only been seen in chimpanzees.
During a two hour period of monitoring a group of gorillas, researchers observed a silverback using his left hand to collect driver ants from a hole in the ground.
When he first inserted his hand into the hole, he quickly removed it and ran away shaking his arm to remove the biting ants.
A female who witnessed what happened, however, then tried it for herself.
After being bitten, she then selected a piece of wood off the ground that was approximately eight inches long that was taped at one end.
She inserted the stick into the hole and then withdrew the stick, licking the ants off of the stick.
Instead they speculate the male gorillas may be simply directing the meal with their songs, providing their group with a signal that they are eating and so should they.
Writing in the journal Public Library of Science One, Dr Eva Maria Luef, from the Max Planck Institute for Ornithology in Germany, and her team said: 'Alternatively, sense of well-being in general may elicit food associated call vocalisations in gorillas.
'The fact that specific foods elicited more calling and simultaneous calling of multiple individuals may indicate that attitude toward, and possibly contentment over, the food source plays some role in the production of food-associated calling in gorillas.
'Food-associated calling could be an expression of well-being in gorillas when feeding on specific, preferred foods.'
This suggests male gorillas may simply be reassuring others in their group that they are happy with the meal they have found.
Singing may also play a role in maintaining group cohesion during mealtimes.
The researchers tracked and studied two populations of wild western lowland gorillas in the Mondika area of the Republic of Congo.
They found whenever the animals were eating they tended to produce two very distinct types of call.
Singing by the gorillas was typified by multiple, short, differently pitched sounds in close succession (spectrogram pictured). The scientists who observed the behaviour said the animals only sing when eating
Female western lowland gorillas (stock picture) and juveniles were not seen to 'sing' or hum as often as the dominant males in the group. This led the researchers to speculate the males may be directing the group's eating activity or perhaps reassuring them that they are happy with the food they are consuming
While singing consisted of multiple, short, differently pitched sounds in close succession, humming was characterised by prolonged low frequency tones.
In other great apes, such as chimpanzees and bonobos, food-related singing has been observed before, however, it is thought to advertise the discovery of tasty morsels to their group.
Many mammals and birds also vocalise when they find or consume food.
However, the behaviour has only been seen anecdotally before in gorillas and the new study is the first to examine it scientifically.
Humming in the gorillas was characterised by prolonged low frequency tones (spectrogram pictured)
The researchers found the gorillas tended to sing and hum more often for specific types of food (a juvenile male eating a fruit pictured). They were most likely to sing when eating aquatic plants, flowers and seeds. Insects however produced the fewest calls
Surprisingly they found the large dominant males tended to sing more than the smaller females and juvenile gorillas in the groups.
Dr Luef and her colleagues now hope to conduct further work to assess what purpose the calls may serve and to see if specific foods produce distinct types of humming or singing.
Dr Luef said: 'Silverback males may have to call more frequently since they are often the ones initiating changes in group activity.'