Meet and Greet in the Dolphin World

By contributing writer Sarah Buckleitner

Many people believe that an important difference between humans and other animals is language--that what has brought us from fields and forests to our comfortable homes is our ability to communicate effectively with one another. And so the discovery that humans are not alone in their power of conversation is one that affects our definitions of our selves, and one opens many research opportunities for scientists.

Research into the calls made by bottlenose dolphins (
Tursiops truncatus) at sea indicates that as dolphin groups encounter one another they exchange unique whistles; researchers claim that the whistles carried information about their identity and alliances with other individuals. In captivity, dolphins and parrots can learn to use signals to convey information about their surroundings, but there isn't much research about whether or not they use these techniques in the wild.

Ed Clayton
Figure 1. A pair of bottlenose dolphins (Tursiops truncatus). (From Ed Clayton/Flickr)

Every bottlenose dolphin has a unique whistle that they develop at a young age and practice while alone. After a call has been established, males and females differ in their use of signature whistles: females' calls tend to stay stable for about a decade, while males' whistles change to reflect alliances with other individuals. They also have been known to copy the unique calls of their companions--similar to a human calling a friend's name to attract his attention.

By using passive acoustic localization while following pods in Saint Andrews Bay, Scotland the researchers found that unique whistle exchanges mainly occurred when groups first encountered each other (Figure 2). They ensured that the whistle exchanges were unique by running a sequence analysis, and also noted that none of the calls were repeated.

whistle1
Figure 2. Spectrograms of repeated whistle sequences (Letters indicate different whistle types). (From Quick and Janik 2012)

Data was collected over the course of six months, and scientists used focal boats to follow pods of dolphins during good weather. Individuals were identified with photos of their dorsal fins, and groups were defined by the distance between dolphins (less than ten meters apart equaled a group). Then using both visual data indicating the position of each dolphin and auditory data, they determined which individual had used which call and when.

By analyzing this data, researchers affirmed that dolphins exchange signature whistles when meeting at sea, and believe that these calls are meant to convey information about their identity (Figure 3). They also found that only one dolphin from each group uses its signature whistle before joining with another group, which could have various explanations:

    whistles2
    Figure 3. A histogram of all whistle exchanges and joining events for dolphin groups. (From Quick and Janik 2012)

    While this study shed new light on the way dolphins use sound to communicate, it also opened up many more questions about how these organisms use signature whistles to interact, and what that means in terms of how humans define themselves.

    References

    Quick, N., & Janik, V. (2012). Bottlenose dolphins exchange signature whistles when meeting at sea Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2537