Recently Lucile wondered if hydrodynamic interactions, such as the ones ongoing in a fish school that allow each fish to spend less energy when compared swimming alone, existed up in the air, upon groups of bird... Yes Lucile ! And bird flocks (collective flying bird groups) - right image - behave in a very similar way to fish schools - left image -, to defend against predators, feed more efficiently and optimise their global energy ! An interesting - and very short ! - article about this phenomenon, [14], discusses the case of great white pelicans, Pelecanus onocrotalus, flying in a uniform speed of 48 km/h, and compares their energy ‘expenditure’ (consumption) when flying alone or ‘in formation’ (in a group) ‘V’ shaped. The authors simply measured the wing-beat frequency from videos they recorded, and the heart rate of the pelicans with an electronic heart-rate logger. Their graph is presented just below: x axis are the different flying modes/altitudes and y axis is the heart rate (for the colored columns) and wing-beat frequency (for the dots). Numbering of dots indicates the position in the group: ‘1’ for being the leader, etc, etc. Evidently, the pelicans save a significant amount of effort/energy by flying in formation, compared when flying alone ! Also, the same results regarding the difference of wing-beat frequencies between individuals of different positions in the group are observed in the first graph of my last post [15], for fish’ tail-beat frequencies: individuals at the front of a group seem to spend more energy than those located at the back or middle of it. This is because each pelicans, or birds from any other bird flocks, uses the air movement and vortex wakes generated from their adjacent neighbours; each wing moves in an upwash field that is generated by the wings of the other birds in the formation. Isn't this extraordinary ?? This energy saving advantage is probably a principal reason for the evolution of flight formation in large birds that migrate in groups (since they’re heavy…). REF: [14] Article: Weimerskirch, Martin, Clerquin, Alexandre & Jiraskova - 2001 - Energy saving in flight formation - Nature, Vol. 413, pages 697-698 [15] Blog Post: Hanaé (me) - 2016 - SCHOOLING TO OPTIMISE HYDRODYNAMIC INTERACTIONS - Weebly: http://stagelfdv.weebly.com/home/schooling-to-optimise-hydrodynamic-interactions Oh no WAIT ! You’re not done with this post yet ! Since reading gets boring, watch this nice TED-Ed video on ‘How do schools of fish swim in harmony ?’ and ‘How do the tiny cells in your brain give rise to the complex thoughts, memories, and consciousness that are you ?’
3 Comments
Leon
9/12/2016 03:14:51 am
Hey ,
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HanaƩ
15/12/2016 02:43:42 pm
Good evening Léon,
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Leon
25/12/2016 02:54:39 pm
My bad i didn't precise that i was talking about predators of bigger size.
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