Meeting Abstract
The beak and beak-braincase interface of woodpeckers are hypothesised to serve as a shock absorber to minimise the harmful deceleration of the woodpecker’s brain upon impact when pecking trees. This idea has become the common believe of how these birds protect their brain against injury, and seems supported by the presence of a relatively large zone of spongy bone at the frontal region of the braincase. However, since any absorption or dissipation of the head’s kinetic energy upon impact implies lower peak forces exerted by the tip of the beak on the tree, evolving any type of shock absorber will probably impair the bird’s hammering performance. To study this ‘woodpecker shock absorption paradox’, we first analysed the kinematics of the upper beak and braincase (eye centre position) based on high-speed videos (up to 4000 frames per second) of two black woodpecker individuals (Dryocopus martius) during pecking, and found that decelerations virtually did not differ between the beak and the braincase during impact, indicating a very stiff beak-braincase interface. Secondly, forward dynamic modelling of wood penetration events by a head with variable degrees of shock attenuation confirms the adaptive advantage of such stiff cranial systems without shock absorption. Finally, numerical modelling predicted that intra-cranial pressure in D. martius safely remained below half of those corresponding to the approximate threshold of concussions in primates. Together, these results show that the multi-component cranial skeleton of the black woodpecker is used as a stiff hammer during pecking to optimise pecking performance, and not as a shock absorbing system to protect the brain.
