New Study by Georgetown Scientists Shows Dolphin Personality Stable for Decades
While a few studies show that human personality traits last a long time, until now, the same has not been shown for wild animals. In a first-of-its-kind study published in Communications Biology, Ph.D. candidate Taylor Evans (G’21) and Janet Mann, Ph.D. and professor in the Department of Biology show that bottlenose dolphins have stable behavioral traits that last for decades.
“This work is exciting because it helps us understand what drives individual differences in behavior, and how dolphins respond to changing environments, whether natural or human-induced,” says Mann. “Additionally, dolphins have high social complexity in that they maintain individually specific long-term bonds over decades. Stable ‘personality’ might be an essential feature of social complexity.”
The Dispositions of Dolphins
In their study, the researchers discovered that “these dolphins display very clear social ‘personalities’ in their behavior.”
“{These personalities} begin to show early on in the calf period and last through old age, despite all the changes dolphins face in their long lives,” says Taylor Evans, Ph.D. candidate and lead author of the study.
Evans has studied personality in other species, including sea anemones, but finds the variation in dolphin behavioral traits most compelling.
“There was a striking range of sociality between individuals, with some dolphins spending almost all of their time alone and others rarely sighted without other dolphins nearby,” explains Evans.
This is comparable to the introverted and extroverted axis in human personality.
Mann, who is senior author of the study, is the leader of the Shark Bay Dolphin Research Project.
“Given that bottlenose dolphins are dependent on their mothers for up to 8 years and live into their 50s —that is, they have slow life histories like humans, other primates and elephants — such stability is remarkable,” says Mann. “Furthermore, dolphins live in a dynamic society characterized by “fission-fusion” – meaning that who they are with changes frequently throughout the day, much like humans. This means they can ‘choose’ when to socialize, hunt or rest – less constrained by what their associates are doing.”
Using 32 years of longitudinal data for 179 dolphins, the scientists were able to show that several measures of social behavior such as the number of associates, time spent alone and time spent in large groups were stable from infancy to adulthood and within the adult period. These measures were also correlated; predictably, dolphins who spent most of their time alone had fewer associates.
Some dolphins tend to be loners while others are much more gregarious, a pattern that carries on throughout their lives. The research team also found that males were less stable across time than females, likely because daughters closely mimic maternal behavior while sons invest considerable time developing social bonds such as alliances that are critically important for mating success.
These findings have important implications for how we think about social behavior.
“Instead of being something easily adjustable and plastic, sociality seems to be a stable preference that dolphins maintain across time and context,” Evans explains. “It’s really important to consider that individuals are not interchangeable, especially given that social connections influence processes like information transfer, disease transmission, and responses to environmental change.”
-by Shelby Roller (G’19)
