Cross-posted from the Times UK
By MARK HENDERSON, Science Editor
To the untrained urban ear, one horse’s whinny might sound pretty similar to the next. To another horse, however, it is the voice of an individual, with scientists showing that the animals can match a face to a neigh.
A study of 24 horses from a Sussex stable has found that all were capable of recognising other members of the herd by their voices, providing the strongest evidence yet for vocal identification in animals.
The results suggest that the equine brain is capable of complex recognition skills that are important for negotiating the pecking order of the paddock.
“If you asked 30 years ago, most scientists thought that only humans had this cross-modal ability to associate voices with individuals,” said Leanne Proops, of the University of Sussex, who led the study.
“We’ve shown clearly that horses have the ability to mix cues from different senses to identify individuals.”
The Sussex team staged an ingenious experiment: first, a subject horse was held still while a second horse from the same herd was led past it, before disappearing behind a barrier. After a wait of ten seconds, the scientists then played a tape recording of a neigh, from the place at which the horse was seen last. The recording was either of the horse that the subject animal had just seen, or from a different horse that was also familiar.
When the subject animal heard a neigh from a different horse, it responded more quickly and looked in the direction of the sound for significantly longer than when the call and horse matched. This indicates that the horse noticed the incongruity between the animal it had seen and the whinny, thus it looked in its direction for longer, bemused by the mismatch.
Similar methods are used to test the observational skills and counting abilities of babies. A baby who sees two toys placed behind a screen, but three toys when the screen is removed, will stare for longer because this does not meet with expectations.
Ms Proops, who is studying for a doctorate in psychology, said the ability to distinguish individuals by their voices could be important in equine social structures. “You need to be able to tell who is above and below you in the pecking order,” she said.
Details of the research are published in the journal Proceedings of the National Academy of Sciences.
Previous studies have demonstrated that individual animals can discriminate between others with nonvisual clues. However, these have left doubt as to whether this demonstrates true identification of an individual, or just the ability to tell that calls from individuals are different. The Sussex study is the first to show that an animal can identify an individual by its call. The Times online >>