Research press release


Nature Physics

Birds of a feather



A Jelicたちは、3台のカメラを用いて400羽の野生のムクドリの群れを撮影し、それぞれの鳥の個々の軌道を三次元で追跡できるようにした。その結果得られた知見は、この集団運動モデルとは食い違っている。つまり、数羽の「最上位の鳥」がはじめに飛行方向を変え、その数羽の鳥は編隊内の互いに近いところにいることがわかったのである。その後、飛行方向の情報は、約0.5秒以内に群れの全ての鳥に伝わる。従って、こうした迅速な情報伝達は拡散的ではなく、むしろ量子物質の相転移や対称性を破る特性を説明する言語を用いて、この集団挙動を記述できる。

Changes to the flight course of a flock of starlings can be described using a linear dispersion model, where information about the altered direction of the first bird propagates to others in a bird-to-bird transfer of information. These results, reported this week in Nature Physics, reveal the underlying mathematical similarities between collective motion in bird flocks and quantum phenomena in bulk systems.

Around sunset, starlings fly in tight formations of a few hundred to tens of thousands, and sometimes up to millions, of individuals. How they manage to move coherently without colliding or breaking up the formation has been debated. One presently supported model states that bird flight is a collective motion, with no particular leader, in which information is diffusively transported between birds.

Asja Jelic and colleagues filmed a flock of 400 starlings in the wild using three cameras, enabling them to track the individual trajectory of each bird in three-dimensions. Their findings conflict with the collective motion model: they found that a few ‘top birds’ change direction first, and that they are positioned near to each other within the formation. The directional information subsequently reaches all the members within roughly half a second. Thus, the rapid information transfer is not diffusive, but rather the collective behaviour can be described using the language of phase transitions and symmetry breaking characteristic of quantum matter.

doi: 10.1038/nphys3035


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