Dolphins Remember Each Other

Long-term social memory, a crucial cognitive faculty, holds ecological significance as it facilitates the identification of memorable social bonds. For species such as the bottlenose dolphin, possession of such memory could serve as a vital tool in evaluating social threats and alliances within their intricate and dynamic social structure, which encompasses socialization, hunting, and other group-related activities. A noteworthy study conducted in 2013 provided evidence that dolphins possess the ability to recognize each other over extended periods, challenging the prevailing perception of their memory span.

In a study disseminated in the esteemed journal Proceedings of the Royal Society B, researchers sought to investigate the capacity of forty-three bottlenose dolphins, living in human care facilities across the United States, to differentiate between the whistles of familiar and unfamiliar individuals. The vocalizations of these dolphins, including their high-pitched whistles produced in social contexts, were meticulously recorded. The researchers used records from six reputable institutions: Brookfield Zoo, Indianapolis Zoo, Minnesota Zoo, Texas State Aquarium, The Seas at Epcot, and Dolphin Quest: Bermuda, which regularly rotated their animals for breeding purposes. Based on these records, the researchers established which dolphins had previously cohabited and which had never encountered each other.

To evaluate their memory, the researchers employed an underwater speaker to repeatedly play recorded whistles of various dolphins and observed the animals' responses. Upon hearing the familiar whistles, the dolphins exhibited reactions such as turning towards the speaker, swimming in its direction, or contacting the gate safeguarding the acoustic equipment. In contrast, when exposed to unfamiliar whistles, the dolphins quickly lost interest and displayed minimal responses. The dolphins' reactions to the whistles of unfamiliar animals diverged significantly from their responses to the whistles of animals they had previously encountered. Notably, whenever the dolphins heard whistle recordings produced by other familiar dolphins, they actively approached the speaker, hovering in its vicinity and whistling to elicit a response. This behavior was observed irrespective of the dolphins' age, gender, or relationship status, encompassing unrelated dolphin pairs cohabiting together and family members.

The study delved into the long-term memory of dolphins that had been separated for varying durations, ranging from four to twenty years. Surprisingly, the quantitative analysis of their reactions revealed that the length of separation had no substantial impact on their recognition of familiar whistles. Regardless of whether they had been apart for five or fifteen years, the dolphins exhibited comparable levels of response. One remarkable example of long-term memory despite separation was Bailey, a female Atlantic bottlenose dolphin who lived at Dolphin Quest Bermuda during the study. For twenty years, she had cohabited with another female dolphin named Allie at the Dolphin Connection in the Florida Keys. The researchers played recordings of their whistles in their current residences, including the Brookfield Zoo, where Allie was living at the time of the study. Remarkably, both dolphins recognized each other's whistles despite not having physically seen each other in two decades.

Several species, not limited to dolphins, exhibit extraordinary memory capabilities. Research has shown that monkeys possess the ability to recognize the faces of fellow monkeys even after a three-year separation, while elephants can recognize the vocalizations of others a decade after their last encounter. This study, conducted by Jason Bruck in 2013, delved into the exceptional memory of dolphins. The study highlighted a remarkable case where a dolphin named Bailey recognized the vocalizations of another dolphin named Allie through an underwater speaker, despite not having physically seen her for twenty years. This suggests that dolphins may possess the longest-held memories among extant animal species, surpassing many others by a significant margin.

Research on bottlenose dolphins has revealed that they approach speakers emitting whistles of relatives rather than those of unfamiliar animals. Additionally, dolphin mothers frequently produce the whistles of their calves when separated, which scientists believe is analogous to calling their "names" to locate them.

These findings raise pertinent questions regarding dolphins' responses to whistles and their cognitive processes. While it is tempting to speculate, the extent to which anthropomorphic concepts such as "names" align with dolphin cognition remains uncertain. Researchers aspire to explore the representation of mental imagery in dolphins in the future to gain a deeper understanding of their cognitive capacities.

Citation:

Bruck, J. N. (2013, October 7). Decades-long social memory in bottlenose dolphins. National Institutes of Health (.gov). Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757989/