Cooperative hunting

Cooperative hunting is when meat-eating animals hunt together in groups that contain both division of labor and role specialization. It is a rare behavior that evolves when two or more individuals successfully capture more prey and suffer fewer costs together than when alone. 80-95% of carnivores are solitary and hunt alone; however, certain species have been found to participate in cooperative hunting, including lions,wild dogs,spotted hyenas,chimpanzees, and humans. In addition to mammals, cooperative hunting behavior has also been documented in birds of prey and large marine vertebrates such as fish and moray eels. Cooperative hunting has been linked to the social organization of animal species and the evolution of sociality and thus provides a unique perspective to study group behavior.

Understanding how cooperative hunting could evolve requires considering the circumstances that would make it beneficial.

In 1988, ecologists Craig Packer and Lore Ruttan surveyed the breadth of documented instances of cooperative hunting to make a game-theoretical model to explain under what circumstances cooperative hunting evolves. In their model, individuals can choose one of four hunting strategies:

Each of these strategies has a certain efficiency based on the size and number of prey that can be captured in a hunt.

The model shows that cooperative hunting for a single large prey is an evolutionarily stable strategy (ESS)--a strategy that an individual adopts because failure to do so reduces the individual’s fitness—only when solitary hunting is much less efficient. This is usually due to a prey species being too large to be taken down by an individual, meaning hunting efficiency is low and hunting cost is high. In this case, the increased benefit in hunting efficiency from cooperation must compensate for the division of available meat among cooperators. Furthermore, cooperatively hunting groups are prone to invasion by cheaters and scavengers who avoid the drawbacks of hunting, so the added benefit of cooperative hunting must also outweigh these costs. Otherwise, cheating and scavenging can also be evolutionarily stable strategies. The proportion of these strategies increases in larger groups, since only a certain number of individuals are required to help make the kill, allowing others to directly benefit without participating in the hunt.

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