Game Theory Explains Unusual Bird Behavior

March 12, 2009

Game theory offers a possible explanation of an unusual foraging strategy used by young ravens, when they search for food in groups rather than individually. Models commonly used by economists to analyze financial trends suggest how this curious behavior arises.

The study "is a rare example of how game theory has been used to predict behavior in animals in the real world," said research team member Sasha Dall of the University of Exeter (Cornwall). It "shows the potential for game theory to help biologists understand how different social structures and behaviors evolve in different environments and in response to human activities."

Ravens feed on the carcasses of large animals. They typically search for food individually, and the finds are then defended by adult pairs. Unpaired younger birds

gather in communal roosts from which they search individually for carcasses but, after a find, recruit other young ravens to help keep away adult foragers.

The researchers identified one raven roost—in Anglesey, Wales—where some juveniles behaved differently. These birds coordinated their foraging, setting out in gangs and roosting separately from other birds.

To better understand, and perhaps predict, this singular activity, researchers designed a mathematical model based on game theory principles and models used by economists to identify the most profitable behaviors of individuals in different situations.

The study revealed that two strategies emerge as evolutionarily stable and most profitable for ravens looking for food. One is for birds to search independently for food, then recruit each other to protect the find. The other is for birds to forage in groups.

Which behavior occurs depends on the local landscape and other factors that influence the availability of carcasses. "Gang-based foraging from independent roosts is likely to appear and persist when searching in groups is not particularly inefficient compared to individuals searching independently and sharing their effort by recruiting from a central roost," the researchers noted. This will be the case if the area searched is not particularly large—for example, it can be searched by a group in a day—or it is in open habitat, within which carcasses are visible from a distance.

The Anglesey roost is in an agricultural, deforested area of Wales where carcasses of farm animals are often available, so food is more plentiful than in wild areas. By operating in gangs, the ravens not only find food readily but also gain social status by being among the "finders" of food.

The study, "Rich Pickings Near Large Communal Roosts Favor 'Gang' Foraging by Juvenile Common Ravens, Corvus corax," appears in PLoS One (25 February 2009).

Source: University of Exeter, Feb. 24, 2009.