It might not be the animal communication Dr Dolittle-style, but researchers have found that humans can glean insights into the feelings of animals such as pigs, horses and goats based on their vocalisations.
The findings suggest that certain information within sounds, such as how intense an animal's emotions, appears to be conveyed in a similar way across species, according to the team.
People probably base their decisions on their knowledge of how humans sound when they are more or less aroused because arousal is linked to stress pathways, which is a system that is well conserved across vertebrates, said Dr Elodie Briefer, co-author of the research from the University of Copenhagen.
They looked at whether people could determine whether an animal was expressing a positive or negative emotion.
We can't really depend on what we know from humans because there are lots of differences in how species express emotions, even closely related ones, said Briefer.
Briefer and colleagues reported in the journal Royal Society Open Science that they recorded vocalisations from six animal species - horses, pigs, goats, cattle, Przewalski s horses wild horses and wild boars. The sound was made when the animal was aroused as determined by a high heart rate or movement, and whether the sound was made in a positive context, such as anticipating food, or a negative context, such as being isolated, according to the team.
The team used existing recordings of meaningless speech spoken in rage or fear to represent higher and lower emotional intensity or arousal, and in an angry or joyful way to suggest a negative or positive context.
The researchers asked 1,024 participants from 48 countries to listen online to a pair of sounds.
For each species, four pairs of vocalisations were played. For two pairs, they were asked to rate the emotional intensity of the sound as high or low, while for the other two pairs they were asked to rate the emotion as positive or negative.
The results showed that the participants correctly rated the emotional intensity of the subject 54.1% of the time, and the type of emotion 55.3% of the time.
When the team examined the data further, they found that participants did better than chance when it came to assessing vocalisations from pigs, horses, goats, humans, and for type of emotion only wild boars.
People are better at recognising domestic than wild species, said Briefer.
The arousal of pigs and horses was correctly rated 59% and 58% of the time, compared to 55% for humans, while their type of emotion was rated correctly 58% and 64% of the time respectively, compared with 68% for humans.
Briefer said that the relatively low success rate for most species, including humans, may be down to the use of the same sound for each vocalisation, such as mooing for cows or whinnying for horses, and that while ratings might have been high for horses, the relatively low success rate for most species, could be down to the use of the same type of sound for each pair of vocalisations, such as mooing for cows or whinnying for horses.
Briefer added that participants' success in rating the types of emotions varied far more than their ability to determine the intensity of the emotions.
She said that if we take it to the next level, we can train people to recognise the sounds, and that could help those working closely with animals from farmers to pet owners to understand them better.
In the past, scientists used to focus on physical health to assess animal welfare. Most people recognize the large role that emotions play in our lives.