Driver-Barrier Behavior: How Dolphins Work Together To Catch A Meal

Figure from Hamilton et al. 2022.

By Mira Johnson, Field Assistant

Like many coasts along Florida, the Nature Coast is home to many resident bottlenose dolphins. But what makes this area an exceptionally remarkable field site for the Cedar Key Dolphin Project is the unique behavior called Driver-Barrier foraging, which is known to only take place there.

Driver-Barrier foraging behavior is a role-specialized foraging tactic performed by bottlenose dolphins to catch mullet. The behavior fittingly received the name, Driver-Barrier, for its involvement of one individual serving the role of Driver and one or more as Barrier(s) to forage. The interaction begins with a Driver rapidly circling a school of mullet in a clockwise direction. As the driver herds the mullet, Barrier dolphins position themselves by the outlet of the closing circle to meet the Driver. Once trapped in the circle, in an attempt to flee, the mullet leap out of the water where the dolphins await the fish with their heads above the surface (see diagram on the right).

What a crazy way to catch fish! But just how do these dolphins coordinate such a complex interaction? This is one of the many questions we are hoping to answer by studying Driver-Barrier using techniques such as video, photography, acoustics, and GPS. Video recordings (i.e., hand held camera, drone, and Insta 360) and photographs help us identify individual dolphins as drivers or barriers and determine how many fish they catch. To investigate the use of vocalizations during Driver-Barrier events, we also submerge hydrophones (underwater microphones) in the water. This device allows us to record whistles that we otherwise cannot hear from the surface! The GPS lets us pinpoint where the Driver-Barrier behavior happens, while the drone allows us to obtain an aerial view of the behavior. Observing from this unique perspective has been very helpful in understanding how the Driver and Barrier work together to herd fish. To see Driver-Barrier in action, watch our video at YouTube!

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From our research, we have learned a lot about this fascinating role-specialized behavior. One of the things we have learned from using acoustics is that echolocation is likely the cue used to coordinate Driver-Barrier behavior. During a Driver-Barrier event, there is a notable lack of whistles which suggests that dolphins must be relying on some other cue than vocalizations to coordinate movement. It is unlikely that the primary cue is visual, as the low water clarity in which Driver-Barrier takes place makes for poor visibility. Therefore, it is thought that dolphins are listening to and reacting to each other's clicks.

Interesting! So echolocation does seem to help coordinate this behavior. But then the question becomes, who is responding to who? Research suggests that Barriers are likely listening to the Driver’s echolocation to coordinate movement and timing. However, whether the Barriers are using the driver’s echolocation directly or indirectly (i.e., eavesdropping) is still unclear. 

As you can see, although there is a lot that we have learned from studying Driver-Barrier, there is still much to be uncovered. As we look forward to this field season, we hope to continue to gather data on Driver-Barrier that will hopefully help us answer some of our next questions, like 1) does every Driver and Barrier work a foraging event in the same way or are there differences in technique? 2) How do dolphins learn this behavior? Is it from their cohorts or from their mothers? All good research leads to more and more questions to be answered!

To learn more about Driver-Barrier, please feel free to read some of the publications by Dr. Gazda and colleagues referenced below. You can find PDFs in our publications section on our website. 

Hamilton, R. A., S. K. Gazda, S. L. King, and R. C. Connor. 2022. Bottlenose dolphin communication during a role-specialized group foraging task. Behavioural Processes. 104691. https://doi.org/10.1016/j.beproc.2022.104691

Gazda, S.K. 2016. Driver-barrier feeding behavior in Bottlenose dolphins (Tursiops truncatus): new insights from a longitudinal study. Marine Mammal Science. doi: 10.1111/mms.12314 (PDF)
Gazda, S.K., R.C. Connor, R.K. Edgar, and F. Cox. 2005. A division of labour with role specialization in group-hunting bottlenose dolphins (Tursiops truncatus) off Cedar Key, Florida. Proceedings of the Royal Society of London Series B-Biological Sciences. 272: 135–140.