By Clare Wilson
“Maaah.” Goat calls might all sound the same to us, but the animals seem to recognise when one of their herd-mates is happy or sad from their bleats alone.
When goats hear a series of calls that change in emotional tone, they look towards the source of the sound – and their heart-rate readings indicate the animals’ own emotions are swayed by the noises.
Luigi Baciadonna of Queen Mary University of London and colleagues recorded goats bleating in different emotional states to see how they are affected by hearing each other’s calls.
To elicit positive sounds, they recorded goats that could see someone approaching with a bucket of food. To get negative ones they let an animal see another being fed while not getting any food themselves, or kept one in isolation for five minutes. “This was not extreme distress – I don’t think most people could tell the difference in their calls,” says Baciadonna.
Bleats with meaning
Then, to a different goat, the team played a bleat every 20 seconds, with nine positive ones followed by three negative or vice versa. At the start, the animal looked towards the source of the sound, but this tailed off as it got used to it. When the switch between emotional bleats happened, the goat was more likely to look again – but only with the second call of the batch of three. “There’s a bit of a delay in spotting the difference,” says Baciadonna.
The team also tried to see how the goats hearing the recordings felt, by measuring the variation in time between each heartbeat. In people, a high value for this is linked with more positive mood, while low values correlate with feeling depressed or stressed. Sure enough, when goats heard the happy bleats, their heart-rate variability was higher than when they heard the sad ones.
“I don’t doubt any of this,” says David Harwood, senior vice-president of the UK’s Goat Veterinary Society. “Goat owners are always telling us how intelligent their animals are.”
Journal reference: Frontiers in Zoology , DOI: 10.1186/s12983-019-0323-z