A new paper says that unpredictability is a consistent trait in the animal world, just like it is humans.

Anyone who owns a cat knows that, right?

Not really. Though animals are known to show consistent individual differences in behavior, and pet owners may refer to it as them displaying 'personality', a new paper refutes prior beliefs and says that some individual animals, just like humans, are consistently more unpredictable than others over time.

Unpredictability is a known and accepted aspect of human behavior much like we've always viewed predictable aspects of personality. However, until now it has never been studied in animals, the authors say.

"We all know someone who is notoriously unpredictable –happy, friendly, supportive one day and grumpy and unhappy the next. My experience is that those people tend to be extroverts. Even though I don't know what to expect of them, I am often torn between liking them because they are easy to talk to and fun to be with, and disliking them for their volatility," said Associate Professor Peter Biro, a behavioral ecologist with Deakin's School of Life and Environmental Sciences and lead researcher on this study. Until now, unpredictability has only been studied extensively in humans, where it has been linked to learning, aging, and to certain diseases that produce erratic behavior due to fluctuations in brain chemicals.

"The results of this new study shed light on another important aspect of animal personality that has previously not been considered."

Working with Dr. Bart Adriaenssens at the University of New South Wales, Biro observed the behavior of adult male mosquitofish over 132 days. They found that the behavior of some individuals was consistently more predictable in a given context than others. Mosquitofish were used for the study because they are widespread and easily sampled from ponds in and around cities.

"We observed that individuals differed in their average levels of activity, but also differed in variability about their average activity," Biro explained. "Some individuals chose to be active, others chose to be sedentary, some were consistent in their chosen level of activity, others not. But, we found no association between activity levels and predictability.

"What this tells us is that the fish differed in how unpredictable they were, and that this unpredictability is a consistent attribute over time.

"We believe that unpredictability might represent a form of behavioral flexibility that facilitates learning, or makes animals unpredictable to predators or competitors. Some have even referred to this phenomenon as representing 'free will' in animals. Our study, having confirmed that unpredictability is a trait, now sets the stage for further studies to test for this phenomenon in other species, and to tease out the causes and consequences of this behavioral variation."

Citation: Peter A. Biro, Bart Adriaenssens, 'Predictability as a Personality Trait: Consistent Differences in Intraindividual Behavioral Variation', The American Naturalist, Vol. 182, No. 5 (November 2013), pp. 621-629 DOI: 10.1086/673213/dryad.h8c10