Horses and Pigs Perceive Hard Sounds – ScienceDaily

Horses and Pigs Perceive Hard Sounds - ScienceDaily

The way we speak matters to animals. Horses, pigs, and wild horses can discriminate between negative and positive sounds from their conspecifics and close relatives, as well as from human speech. This, according to new research in behavioral biology at the University of Copenhagen. The study provides insight into the history of emotional development and opens up interesting perspectives regarding animal welfare.

The idea of ​​horse whisperers – those with a knack for communicating with horses – may make many laugh. But according to new research from the University of Copenhagen and ETH Zurich, there could be something to their whispering abilities. As part of an international collaboration, with researchers Anne-Laure Maigrot and Edna Hillmann, behavioral biologist Elodie Briefer from the Department of Biology at the University of Copenhagen investigated whether a range of animals could distinguish between positively and negatively charged sounds.

“Results showed that domestic pigs and horses, as well as Asian wild horses, can tell the difference, both when sounds come from their own species and close relatives, as well as from human voices,” explains Elodie Briefer. Pigs have been studied along with wild boars, their wild relatives. Just as with the two related horse species, the pigs clearly reacted to how emotionally charged the sounds of their counterparts were. In fact, to the same extent as when it came to sounds of their own kind.

Animals have even shown the ability to distinguish between positively and negatively charged human voices. While their reactions were more subdued, all but the boars reacted differently when exposed to human speech laden with positive or negative emotions.

human gibberish

Researchers played recordings of animal sounds and human voices from hidden speakers.

To prevent pets from reacting to specific words, positive and negative human speech was performed by a professional voice actor into a kind of gibberish without any meaningful sentences.

The animals’ behavioral responses were recorded in a number of categories used in previous studies – everything from the position of their ears to their movement or lack thereof.

Based on this, the researchers concluded that: The way we speak matters to animals.

“Our results show that these animals are affected by the emotions we charge our voices with when we talk to them or are around them. They react more strongly – usually faster – when encountered with a negatively charged voice, compared to those who have a positively charged voice is first addressed to them. In certain situations, they even seem to reflect the emotion to which they are exposed” specifies Elodie Briefer.

Do animals have an emotional life?

Part of the purpose of the study was to investigate the possibility of “emotional contagion” in animals – a sort of mirror of emotion. Situations where an expressed emotion is assumed by another. In behavioral biology, this type of reaction is considered the first step in the category of empathy.

“If future research projects clearly demonstrate that these animals reflect emotions, as this study suggests, it will be very interesting in terms of the developmental history of emotions and the extent to which animals have an emotional life and a level of consciousness,” says Élodie Briefer.

The study was unable to detect clear observations of “emotional contagion”, but one interesting result was in the order in which the sounds were delivered. The sequences in which the negative sound was played first elicited stronger reactions in all but the boars. This included human speech.

According to Elodie Briefer, this suggests that the way we talk around animals and how we talk to animals can have an impact on their well-being.

“This means that our voices have a direct impact on the emotional state of animals, which is very interesting from an animal welfare point of view,” she says.

This knowledge not only raises ethical questions about how we perceive animals, and vice versa, it can also be used as a concrete way to improve the daily lives of animals, if those who work with them know about it.

“Where animals have reacted strongly to hearing negatively charged words first, so does the other way around. That is, if initially addressing animals in a more positive voice and friendly, when they are met by people, they should react less. They can become more calm and relaxed”, explains Elodie Briefer.

The next step for the researcher from the University of Copenhagen is the switchover. She and her colleagues are now studying how well we humans are able to understand the emotional sounds of animals.

How the researchers did

  • The animals in the experiment were either privately owned (horses) or from a research station (pigs) or lived in zoos in Switzerland and France (Przewalski’s wild horses and wild boars).
  • The researchers used animal sounds with a previously established emotional valence.
  • Animal sounds and human voices were played to animals from hidden speakers.
  • This required high sound quality to ensure that the natural frequencies were best heard by the animals.
  • The sounds were played in sequences with either a positive or negatively charged sound first, then a pause, — and then sounds with a reverse valence, ie the reverse emotion.
  • The reactions were recorded on video, which the researchers were then able to use to observe and record the animals’ reactions.

Three theses can explain animal reactions

The researchers worked with three theories about the conditions they hoped to influence the reactions of the animals in the experiment:


  • According to this theory, according to the evolution of species, i.e. evolutionary history, animals with a common ancestry may be able to perceive and interpret the sounds of others by virtue of their biology common.


  • Close contact with humans, over a long period of time, may have increased the ability to interpret human emotions.
  • Animals capable of sensing human emotions might have been preferred for breeding.


  • Based on learning. The specific animals in the study may have learned to better understand humans and other species, with whom they were in close contact where they were housed.

The conclusion is as follows. Of the horse species, the phylogeny thesis best explained their behavior. On the other hand, the behavior of porcine species corresponds best to the domestication hypothesis.

The study was initiated at ETH Zürich and funded by the Swiss National Science Foundation