Animal Migration Routes Maintained by Knowledge of Informed Elders

A new model of animal migration patterns suggests that an entire migratory route can be changed if just a few so-called "informed individuals" are removed from the larger group.

A team of European researchers report that a migratory route can disappear completely if enough informed individuals are removed.

Using bluefin tuna in Norway as a base, the researchers modeled the migration of bluefin through the region. Until the 1950s the region was saturated with bluefin tuna as they migrated through the waters there each year. The predictable presence of the fish supported a thriving fishing industry. But suddenly, over the course of just 4 or 5 years, the fish stopped migrating through the region.

This sudden erasure of a migratory route was the inspiration for the new migration model, which was developed by Giancarlo De Luca from the International School for Advanced Studies of Trieste (SISSA) and an international team of researchers from the Centre for Theoretical Physics of Trieste and the Technical University of Denmark.

"We started out by taking inspiration from the phenomenon that affected the bluefin tuna, but in actual fact we then developed a general model that can be applied to many situations of groups 'on the move'," said De Luca.

De Luca treats the collective behavior as a function of self-organization of each individual's behavior.

"The majority of individuals in a group may not possess adequate knowledge, for example, about where to find rich feeding grounds," De Luca explained. "However, for the group to function, it is enough that only a minority of individuals possess that information. The others, the ones who don't, will obey simple social rules, for example by following their neighbors."

"When the number of informed individuals falls below a certain level, or the strength of their determination to go in a certain direction falls below a certain threshold, the migratory pathway disappears abruptly," he said.

The most informed fish are, presumably, the oldest (and largest) in the group, making them prime targets of fishing operations. If too many of these large, informed fish are eliminated, the migration route may disappear as well.

De Luca calls these big, old fish "knowledgeable elders." Incidentally, if there are too many of these knowledgeable elders in a group, they stop playing a valuable role, he said.

"In fact, above a certain number of informed individuals, the group performance does not improve so much as to justify the "cost" of their training. The best cost-benefit ratio is obtained by keeping the number of informed individuals above a certain level, provided they remain a minority of the whole population."

De Luca and his colleagues published their work in the Journal of The Royal Society Interface.