2013年9月11日水曜日

Context-dependent hierarchies in pigeons

Máté Nagy, Gábor Vásárhelyi, Benjamin Pettit, Isabella Roberts-Mariani, Tamás Vicsek, and Dora Biro
PNAS August 6, 2013 vol. 110 no. 32 13049-13054

ハトの社会階層の話。
「日頃の社会的支配/被支配関係(例:誰が餌を先に食べる権利を持つか)」と「群れで移動する際のリーダー/フォロワー関係(例:誰が行き先を決めるのか」は一致しなかった。言い換えると、「日頃の社会的関係において優位な個体」と「移動の際にリーダーとなる個体」は異なっていた。
つまり、ハトの社会階層は固定されたものではなく、状況によって柔軟に変わり得る。

Hierarchical organization is widespread in the societies of humans and other animals, both in social structure and in decision-making contexts. In the case of collective motion, the majority of case studies report that dominant individuals lead group movements, in agreement with the common conflation of the terms “dominance” and “leadership.” From a theoretical perspective, if social relationships influence interactions during collective motion, then social structure could also affect leadership in large, swarm-like groups, such as fish shoals and bird flocks. Here we use computer-vision–based methods and miniature GPS tracking to study, respectively, social dominance and in-flight leader–follower relations in pigeons. In both types of behavior we find hierarchically structured networks of directed interactions. However, instead of being conflated, dominance and leadership hierarchies are completely independent of each other. Although dominance is an important aspect of variation among pigeons, correlated with aggression and access to food, our results imply that the stable leadership hierarchies in the air must be based on a different set of individual competences. In addition to confirming the existence of independent and context-specific hierarchies in pigeons, we succeed in setting out a robust, scalable method for the automated analysis of dominance relationships, and thus of social structure, applicable to many species. Our results, as well as our methods, will help to incorporate the broader context of animal social organization into the study of collective behavior.

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