Dolphin Research at the Aquarium

More than 30 years ago, a groundbreaking report demonstrated that our closest relative, the chimpanzee, had an ability that had been previously thought to be uniquely human—mirror self-recognition (MSR). Until recently, this indicator of self-awareness has seemed limited to humans and apes.

MSR is thought to correlate with higher forms of empathy and altruistic behavior and, apart from humans and apes, dolphins and elephants are also known for such capacities.

By using the mirror as a research tool, Diana Reiss has conducted comparative investigations of MSR with dolphins to further elucidate the nature of intelligence in this species. The bottlenose dolphin shows social, behavioral, and cognitive complexity comparable to that of the great apes, and thus was a compelling candidate for a study of MSR.

Developmental studies of MSR in dolphins of different ages are needed to gain a clearer understanding of when this ability emerges and how it correlates with other stages of social and cognitive development. MSR emerges in children between 18 and 24 months and correlates with the onset of other behaviors indicative of empathy and theory of mind. In young chimpanzees, this ability emerges at about 4 years of age.

MSR is thought to correlate with higher forms of empathy and altruistic behavior and, apart from humans and apes, dolphins and elephants are also known for such capacities.

Reiss is collaborating with the National Aquarium’s head of Biological Programs, Sue Hunter, on this research program with the Aquarium’s dolphins.

Scientific evidence indicated that noise may be a source of stress for bottlenose dolphins. Investigations in 2005 indicated the need for further study and led to the development of a noise-recording system.

The system allows continuous monitoring of underwater noise in the dolphin pools and recording and analysis of sounds. The system has also allowed staff to monitor sound levels during specific events such as drilling and jackhammering in areas adjacent to the pools, concurrent with observations of dolphin behavior.

Researchers concluded that, in mammals, exposure to high-intensity sound can cause tissue damage, hearing loss, and altered behavior. The effects of lower-intensity sounds may include disrupted rest, a startle response, annoyance, fear, increased aggression, and physiological changes associated with stress.

In 2008, the addition of two new hydrophones provided more accurate data on noise in the pools, particularly sounds in the low-frequency range.

The National Aquarium collects acoustic recordings of the sounds our dolphins make. The recording system was implemented in order to discover whether environmental noises cause changes in dolphin behavior. Noise events were noted, and recordings were made to determine the level of the sound in the pool. In addition, dolphin vocalizations were recorded and stored.

We have previously reported that dolphins produce a predominant and shared rising whistle contour we have termed "whistle type 2" that is individually distinctive and may serve as a contact call among animals. We have also described many other whistle types and signals in their repertoire, including a call used in maternal disciplinary contexts.

New data we have more recently collected suggest that dolphins may also produce a distress call when ill or injured. The next step in this research project is to analyze recent recordings to determine whether dolphins emit a distress call.

If such calls are produced, they have the potential to serve as an important indicator of pain, illness, or distress in stranded, rehabilitated, captive, or free-ranging animals. Therefore, the discovery and confirmation that dolphins produce a distress call would be a critical advancement in animal welfare science and could positively impact our veterinary care and management of captive and free-ranging dolphins.