Function and biomechanics of head-bobbing in pigeons
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1
Queen's University, Department of Psychology, Canada
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2
Queen's University, Department of Biology, Canada
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3
Queen's University, Department of Mechanical Engineering, Canada
Head-bobbing in pigeons and other birds is widely considered an optokinetic response which ensures retinal image stabilization during the hold phase and rapid transition into a new position during the thrust phase. However, similar retinal image stabilization is achieved by many other birds and most other vertebrates by means of saccadic eye movements. It is not clear why some bird species developed the potentially more expensive strategy of head-bobbing.
In our experiments, we conducted a detailed analysis of both the kinematics of body and head and the kinetics of the reaction forces exerted on the ground to explore the effects of head-bobbing on the biomechanics of locomotion. Pigeons were trained to walk back and forth between two feeders. In doing so, they traverse two force plates. Equipped with passively reflecting markers, we also register the kinematics of head and body by means of high-speed optical motion capture technology.
We estimate energy consumption by modelling pigeon gait in terms of the dynamics of an inverse pendulum – a model that has been applied successfully the bipedal walking of humans. According to this approach negative work is performed when a foot first strikes the ground, which then has to be compensated with positive work in order to lift the foot off the ground half a gait cycle later. Without any means to transfer energy between these two phases, the walking animal has to come up with the metabolic energy to cover both types of work. Any means to store the negative work exerted at heel strike and exploit it as a source for the positive work required during push-off would make locomotion energetically more efficient.
We present a model which indicates that head-bobbing can provide this function. It assumes that the neck functions as a spring that connects the masses of body and head. Thus, it periodically transforms the kinematic energy of the head as it moves relative to the body alternates into elastic energy that it contains in its extreme positions. We show that the phase of the head-bobbing behaviour relative to the leg movements and both the amounts and the timing of the horizontal ground reaction forces measured over the gait cycle support this model.
In conclusion, we show that rather than being energetically costly, as it may first seem, head-bobbing can help to reduce overall energy consumption during locomotion by transferring work between different phases of the gait cycle. Independently of improving energetic efficiency, it can be used to derive the required push-off force by means of muscles in the neck rather than in the feet. The strategy may thus be used by birds with legs that are thin and poorly equipped for forceful push-off.
Acknowledgements
This study was funded by NSERC and CIfAR
Keywords:
Biomechanics,
head-bobbing,
Locomotion,
Optokinetic Response,
pigeon
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for Participant Symposium)
Topic:
Motor Systems
Citation:
Troje
NF,
Kroker
AM,
Bobyn
K and
Li
Q
(2012). Function and biomechanics of head-bobbing in pigeons.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00351
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Nikolaus F Troje, Queen's University, Department of Psychology, Kingston, Ontario, K7L3N6, Canada, troje@yorku.ca