Do horses remember each other?

Q.I recently hauled my horse into a boarding stable to ride. He’d never been there before, but there was one horse he saw and cried to, and they both got very excited, whinnying and calling to each other. I could swear by how they acted they could be old friends, and it got me wondering if they had met in the past. Is it possible for a horse to remember old acquaintances and herdmates?

—Via e-mail

A.With so many stories describing enthusiastic reunions between horses that had been separated for years, it’s tempting to believe that they must remember past companions. But scientific evidence for long-term individual recognition in horses is lacking, so the answer to your question is “maybe.” Here’s what we do know:

Horses recognize individuals in their current social group.

There’s no doubt that horses can remember individuals in their current social network; they recognize and treat familiar horses differently from one another. Individual recognition is widespread across animals; it insures stability of the social group because each member can distinguish between allies, competitors, neighbors, and strangers.

Unique “signature” cues communicate an individual’s identity to others. Horses can tell one another apart by sight,1 sound, and odor. Horses whinny to maintain contact over long distances; this call also reveals the horse’s size, sex, and identity2. Horses sniff each other to gather information from body odors3, and they detect airborne pheromones using the flehmen response4. Horses also spend a lot of time smelling feces, which conveys information about sex, social status, and identity: In one study, horses spent more time smelling the feces of others that had been aggressive toward them in the past.5

Other animals remember past acquaintances over months or years.

How long a horse’s memory of former acquaintances persists after they are separated hasn’t been studied, but long-term individual recognition over months or years has been documented for other animals, including birds, seals and sea lions, and monkeys.

Long-term social memories are influenced by the nature of the relationship between two individuals and what happens while they are apart. Were they companions, competitors, or casual acquaintances? Did they spend a day or a decade together? In some animals, past opponents and dominant members of the group are remembered best, while in others memories of friends and collaborators are more lasting. If an animal joins a new social group old memories might fade, replaced by memories of current companions.

Horses are an obvious choice for research on long-term individual recognition.

In the absence of scientific research, people tend to form opinions based on anecdotal evidence, but this information can be one-sided. For example, we rarely hear stories about horses that don’t remember past acquaintances, but I will share one here. Last fall my mare was reunited with a former companion; they had been pasturemates for six years, and then apart for 10 years. I couldn’t wait to see how they would greet each other, and I expected a lot of excitement. Instead, after a bit of sniffing, they completely lost interest in one another. Did this reaction mean they forgot, or was it that they remembered each other so well that an elaborate greeting was unnecessary? This raises another unresolved question—how do horses typically react when they meet up with past acquaintances?

Horses are an obvious choice for future research on long-term individual recognition. Maybe a budding equine scientist will take up the challenge and provide a definitive answer to your question: “Can a horse remember an old acquaintance?”


References

1Proops, L., McComb, K. and Reby, D. (2009). Cross-modal individual recognition in domestic horses (Equus caballus). PNAS 106(3), 947-951.

2Lemasson, A., Boutin, A., Boivin, S., Blois-Heulin, C., and Hausberger, M. (2009). Horse (Equus caballus) whinnies: A source of social information. Animal Cognition 12(5), 693-704.

3Péron, F., Ward, R., and Burman, O. (2014). Horses (Equus caballus) discriminate body odour cues from conspecifics. Animal Cognition 17(4), 1007-1011.

4Marinier, S.L., Alexander, A.J., and Waring, G.H. (1988) Flehmen behavior in the domestic horse: Discrimination of conspecific odours. Applied Animal Behaviour Science 19(3-4), 227-237.

5Krueger, K and Flauger, B. (2011). Olfactory recognition of individual competitors by means of faeces in horse (Equus caballus). Animal Cognition 14(2), 245-257.