Hunting Together in the Animal Kingdom

Lions do it, hyenas do it, orcas do it—they hunt in groups. To be more precise: they cooperate when they hunt. While psychologists are most interested in whether and how these mammals form a shared goal, biologists are most interested in their success. Evolutionary biology tells us that cooperative hunting must be adaptive or helpful for individual survival and reproduction; otherwise, we would not observe it today. It has evolved because those lions, orcas or hyenas who somehow coordinated their actions while hunting were probably more successful than the ones who did not. They outperformed the lone hunters and could reproduce better.

Source: R.Winkelmann, used with permission

Cooperation in the ocean

But cooperative hunting does not only occur within a species, it even happens across species boundaries. The biologist Redouan Bshary became famous by investigating cooperation between different fish species in coral reefs. He has found that groupers often hunt together with moray eels, wrasses or octopuses. Groupers are quite large and often cannot fit in the crevices of reefs where their prey hides. Thus, they team up with smaller and more agile fish species.

When a grouper has spotted a potential prey fish, it indicates it to its hunting partners by positioning itself vertically with its head down in front of the hiding place. This signal is only executed when potential hunting partners are nearby and can respond. Once the signal is given, the partners respond by inspecting the reef crevices indicated by the grouper. Finally, one of the two partners will catch the prey, either the grouper standing on guard or their agile partners who catch the prey in the reef crevices. It is important that both of them are sometimes successful, otherwise they would not join the hunt next time (Vail et al. 2013)

But this is not the only inter-species hunt in the ocean. A very recent study has investigated how dolphins hunt with humans in Brazil (Cantor et al. 2023). Traditional net-casting fishers wait in the lagoon for wild bottlenose dolphins to appear. The fishers then watch the dolphins’ behavior, looking for cues that tell them when to cast their nets to catch fish. Not only do the dolphins indicate where the prey is—mullets in this case—they even herd mullet schools towards the fishers! Dolphins then give a cue to the fishers to cast their nets. This form of cooperative hunting is extremely successful: fishers catch nearly four times more mullet and dolphins have a 13 percent increase in survival rates.

Success

Indeed, hunting success is what matters most in whether such cooperative behavior is established. Thus, will we keep hunting dolphins at some point, as we keep hunting dogs? I am afraid not, as it is predicted that the future of the cooperative hunting of fishers and dolphins in Brazil is threatened. The populations of mullet continue to decline. At some point, the joint hunt will probably not make sense anymore, not for the fishers and not for the dolphins, because the hunting success will decline for both of them. As a result, this art of this unique fishing practice might die out. What a pity.