Cooperative Hunting in Dolphin Schools
Bottlenose dolphins are widely known to be relatively smart in comparison to other animals. When comparing a human’s ratio of the actual brain mass to the predicted brain mass, our encephalization quotient ranks to be 7.4-7.8, and that of the dolphin’s is ranked directly after us at 4.14. Brain size is one of the more prominent indicators of the intelligence of a living thing. Another factor that is indicative of intelligence is flock size. Dolphins hunt in packs and have complex social systems, and the cooperative hunting technique is an appropriate example of power ranking in a social network.
Cooperation in the hunting techniques of a school of dolphins exhibits a network exchange theory of sharing the prey amongst other dolphins in the pod. As mentioned in class, we learn that people’s payoffs from negotiation in the theory of network exchange are a combination of obtaining the most money and some notion of being treated fairly. It is a play of the Dictator game, where any individual would prefer to feel like they treat others well in addition to gaining from the exchange. In the case of dolphins hunting for prey, the payoff would entail the amount of fish they can catch as prey.
The two methods of hunting include the “wall method” and the “horizontal carousel method”. As described in the research paper “A Hybrid, Multi-Agent Model of Foraging Bottlenose Dolphins”, the wall method consists of a group of dolphins driving the fish to a wall, either consisting of the shore or another group of dolphins, and they feed off their prey when they bounce off the wall. The carousel method is a formation of a group of dolphins in a tight circle around the fish and the circle gets tighter and smaller until the formation is small enough for the dolphins to feed off the fish by charging at them.
During hunting, the dolphins that belong to a specific school correspond to a specific network layout, with the largest dolphin of the school being the leader and thus the node with the most power in the network. The largest male dolphin would be the leader, and its responsibility is to search an unexplored area and assess the risk and gains of the surroundings. When a new area is being explored, the role of the leader is to form a subset of less dominant dolphins to examine the area and serve as second leaders in command. This means that instead of interpreting the situation as a loss for the leader who would have otherwise had all the fish to himself, the designation of “sub-team” leaders increases the chances of catching fish for food for the leader and reducing the risk of running into predators due to the extra pairs of vigilant eyes. This corresponds to the network exchange theory, where the leader is linked to all the dolphins in the school, and the sub-leaders are the second in command that are linked to subsets of the main herd that they each lead. The closer a particular dolphin in the herd is in communication to the leader, the more power it possesses out of the main herd.
As the number of fish each dolphin is able to eat varies during the hunting period, the stability of the outcome can either depend on the number of fish each pair of dolphins (nodes) in the school (network) can eat or the lack of risk being eaten by a predator. The outcome of the network is stable then if any pair of dolphins in the school eat a total of more than one fish or neither of the dolphins of the pair get eaten by a predator. With the increase of the number of dolphins in the network, the school is safer in numbers as more dolphins will have more power in the herd as they would be required to look out for any danger to the herd during feeding.
Sources:
http://users.ece.gatech.edu/~magnus/Papers/hre_ADHS09.pdf
http://en.wikipedia.org/wiki/Encephalization_quotient