ROLE OF BEAK MORPHOLOGY IN IMPACT PROTECTION OF WOODPECKER BRAIN
– A FINITE ELEMENT STUDY
Lizhen Wang1, Jason Tak-Man Cheung2, Fang Pu1, Deyu Li1, Ming Zhang3, Yubo Fan1,*
1
Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Science and
Medical Engineering, Beihang University,
2
Li Ning Sports Science Research Center, Beijing
3
Department of Health Technology and Informatics, The Hong Kong Polytechnic University;
*email: [email protected]
INTRODUCTION
Human head impact injuries caused by a sudden force
impact are very common in aviation lifesaving, car crash
accident, war or sports activities. Yet, an intriguing example
of nature is woodpecker which is free from head injury even
it drums trunk continually at a speed of about 6-7 m/s and a
deceleration of about 1000g [1,2]. Woodpecker must have
special morphology to attenuate repetative impact force to
sustain rapid pecking without skull or brain injury. In this
study, the biomechanical role of woodpecker beak
morphology during impact was investigated using the finite
element (FE) approach.
METHODS
A three-dimensional (3D) FE model of woodpecker head
was developed (Fig.1-b) based on the actual geometry of
woodpecker obtained from micro-CT images (Skyscan1076,
Skyscan, Belgium) with spatial resolution of 18 μm.
(a)
(b)
which was considered as one single body within the skull
without considering the cerebral-spinal fluid (CSF). The FE
results were validated based on kinematics measurements.
Different FE simulations were done having the whole head
collided with a rigid wall at an initial velocity of 0.05m/s,
0.5m/s, 1m/s, 3m/s and duration of 10-20 ms. Parametric
analysis was done by changing the relative length of the
upper and lower beak of the FE model (Fig.1-b,c,d) to
evaluate its biomechanics effects on brain displacement and
strain during beak impact.
RESULTS AND DISCUSSION
The outer tissue layer covering the upper beak was 1.6 mm
longer than that of the lower beak; on the contrary, the high
strength bone structure of the upper beak was about 1.2 mm
shorter than the lower beak. It was expected that length
variation with upper and lower beaks would influence the
impact mechanics with the tree trunk and load transmission
to the brain. Brain injury was shown to correlate with strain
and strain rate [4]. By comparing the FE predicted strain at
the anterior and posterior cerebrum as well as the anterior
cerebellum during impact (Fig. 1-b,c,d), it was found that
equal upper and lower beak length consistently induced
higher Green Lagrange strains at all three locations of
woodpecker brain.
Table 1: Predicted peak Green Lagrange strain of three
selection regions of the brain during pecking.
Peak Green Lagrange
Three location on the brain
strain ( μ )
BeakLower>BeakUpper
BeakLower=BeakUpper
BeakLower<BeakUpper
(c)
(d)
Anterior
cerebrum
Posterior
cerebrum
Anterior
cerebellum
0.04
0.69
0.08
0.02
0.03
0.05
0.06
0.11
0.18
CONCLUSIONS
Of the many features characterizing birds, the beak is iconic
especially for the woodpecker. A longer lower beak bone
was found to reduce the strain of the brain effectively during
impact. Beak morphology was found to affect impact
mechanics and tissue strain, which might play an important
role for preventing woodpecker brain injury.
REFERENCES
Figure 1: (a) The micro-CT image of great spotted woodpecker head; and
FE model of the (b) BeakLower>BeakUpper, (c) BeakLower=BeakUpper, (d)
BeakLower<BeakUpper.
The model consisted of skull, upper/lower beak, hyoid and
brain. The material properties of skull and beak, hyoid were
derived from mechanical tests. Viscoelastic properties of
human brain [3] was assumed for the woodpecker brain,
1. Spring, L. W. Condor 67, 457-488, 1965.
2. May, P. R.et al. Archives of Neurology 36, 370-373, 1979.
3. Stalnaker,R. Mechanical properties of the head, West Virginia
University. 1969.
4. Lee, M.C. et al. Journal of biomechanics 22, 537-542, 1989.
ACKNOWLEDGEMENTS
National Natural Science Foundation of China (Grant No.10925208) and
the National Key Lab of Virtual Reality Technology for funding.