When Mimicry Matters: Sheep Mimic Important Individuals And Behaviours

Social animals routinely mimic the behaviors of their social partners.  This ubiquitous phenomenon is the cornerstone of group cohesion and effective group functioning. After all, if each individual acted independently of the others in its group, the group would diffuse and cease to exist. As a result, it is the nature of social beings to mimic one another. As Louis Armstrong said, “When you’re smiling, the whole world smiles with you.”

Much of this social mimicry is nonconscious and automatic, such as yawning when someone else yawns or laughing when others laugh. In fact, it is suggested that nonconscious behavioral mimicry is so prevalent that it often goes unnoticed, instead, it is the absence of mimicry that sometimes stands out and signals to us that something is not right.

While it is clear that behavioral mimicry is necessary and beneficial for group-living, the mechanisms underlying this phenomenon are unclear. Not every behavior is mimicked all the time. So, what determines whether a behavior is mimicked or not?

We addressed this question using a wild population of bighorn sheep in the Rocky Mountains of Canada.  Bighorn sheep live in complex social groups that undergo fission-fusion dynamics, similar to humans. This means that the individuals present within a social group change regularly, and sheep must keep track of many different relationships and decide who to stay with when a group fissions (a decision that is likely to depend, at least partially, on mimicry of others). We used vigilance behavior (i.e. an animal raising its head from grazing to scan its surroundings) to examine how behavioral mimicry spreads from one individual to the next. Vigilance behavior is a frequent and easily observable behavior, making it feasible to study in wild animals.

In our first study, we examined whether behaviors were more likely to spread between social partners that possessed characteristics thought to increase their attentiveness towards one another. The underlying mechanism proposed is that individuals with a desire to remain in the same group (e.g. relatives, affiliates, etc.) will pay greater attention to one another, and this greater attentiveness will translate into a higher likelihood of mimicking the behavior of that individual. The relationship between social partners was examined through their proximity to one another, the amount of time the individuals spent together, whether the individuals were oriented in the same direction, the age of each individual, and their hierarchical rank within the group.

In our second study, we assessed whether particular attributes of the behavior being performed made it more or less contagious.  We examined the time it took for an animal to raise its head from grazing, how long they gazed in a single direction for, whether they ceased chewing when they became vigilant, and whether they looked in multiple directions before returning to grazing.  Once again, we predicted that the cues that increased attentiveness towards the vigilance behavior would make that behavior more contagious. We also investigated whether these vigilance behavior cues differed between instances of vigilance that were routine (i.e. randomly scanning the environment) vs. induced (i.e. something in the environment stimulated the animal to raise its head).

If induced vigilance bouts are characteristically different from routine bouts, then animals may learn to use these cues to inform their own vigilance behavior. For example, if an animal raises its head faster in the presence of an inducing stimulus, such as a potential predator, then other animals may learn to associate the quicker head raise with the presence of a relevant stimulus and respond accordingly. However, it may also be that quicker head-raises are atypical and therefore “stand out” and attract the attention of nearby animals. These two mechanisms are not necessarily mutually exclusive and may work together to create situations in which mimicry occurs.

With regards to the relationship between neighboring individuals, we found that mimicry was greater when animals were closer together, when they were oriented in the same direction, and when they were associates (i.e. they spent a large proportion of their time beside one another). We also found that animals of similar rank were more likely to mimic one another, which may be related to association status, as similar aged/ranked individuals are more likely to affiliate. These findings support the idea of a positive feedback loop for keeping social groups together: affiliated individuals pay more attention to one another, and as a result, are more likely to mimic one another. This mimicry, in turn, keeps individuals close to one-another (both physically and attentively), and they continue to affiliate.

With regards to the attributes of a behavior that could affect rates of mimicry, we found that only one of the four variables we examined affected whether the behavior was contagious. That variable is whether an animal ceases chewing upon becoming vigilant. Surprisingly, rates of contagion increased 4-fold when an animal ceased chewing, suggesting that it is an important variable that is potentially attention-grabbing.

As the lead author of the study notes, “While I was surprised that none of the other three variables led to an increase in mimicry, I was not surprised to see the large effect size associated with chewing cessation. As someone who has worked with horses for many years, I have noticed that not only other horses but also many people are very attentive to a horse’s vigilance behavior when they cease chewing.”

Future research would benefit from testing whether this is a universal finding that can be replicated both within and across a variety of different grazing species. Furthermore, assessing whether age plays a role in the development of this mimicry response would assist in teasing apart the two proposed mechanisms for mimicry mentioned above: learning by association, or attentiveness to the behavior.

Overall, these studies indicate that both the relationship between two individuals and how a behavior is performed, contribute to the likelihood of a behavior being mimicked. Nonconscious behavioral mimicry is an important aspect of effective social functioning in both humans and other social animals, and we are only beginning to understand why and how behaviors spread throughout these groups.

These findings are described in the article entitled Doing what your neighbour does: neighbour proximity, familiarity and postural alignment increase behavioural mimicry, recently published in the journal Animal Behaviour. These findings are also described in the article entitled Vigilance behaviour is more contagious when chewing stops: examining the characteristics of contagious vigilance in bighorn sheep, recently published in the journal Behavioral Ecology and Sociobiology. This work was conducted by Petra L. McDougall and Kathreen E. Ruckstuhl from the University of Calgary.