Acta Mechanica Sinica

, Volume 31, Issue 2, pp 181–190 | Cite as

How does a woodpecker work? An impact dynamics approach

  • Yuzhe Liu
  • Xinming QiuEmail author
  • Tongxi Yu
  • Jiawei Tao
  • Ze Cheng
Research paper


To understand how a woodpecker is able accelerate its head to such a high velocity in a short amount of time, a multi-rigid-segment model of a woodpecker’s body is established in this study. Based on the skeletal specimen of the woodpecker and several videos of woodpeckers pecking, the parameters of a three-degree-of-freedom system are determined. The high velocity of the head is found to be the result of a whipping effect, which could be affected by muscle torque and tendon stiffness. The mechanism of whipping is analyzed by comparing the response of a hinged rod to that of a rigid rod. Depending on the parameters, the dynamic behavior of a hinged rod is classified into three response modes. Of these, a high free-end velocity could be achieved in mode II. The model is then generalized to a multihinge condition, and the free-end velocity is found to increase with hinge number, which explains the high free-end velocity resulting from whipping. Furthermore, the effects of some other factors, such as damping and mass distribution, on the velocity are also discussed.

Graphical Abstract


Woodpecker Muscle torque High impact velocity  Whipping Hinged rod 



The authors gratefully acknowledge the support of the National Natural Science Foundation of China (NSFC) (Grant 11372163) and the National Fundamental Research Program of China (Grant 2011CB610305). The third author (T.X. Yu) gratefully acknowledges the support of the NSFC Key Project 11032001.


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Copyright information

© The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Yuzhe Liu
    • 1
  • Xinming Qiu
    • 1
    Email author
  • Tongxi Yu
    • 2
    • 3
  • Jiawei Tao
    • 1
  • Ze Cheng
    • 1
  1. 1.Department of Engineering MechanicsTsinghua UniversityBeijingChina
  2. 2.Department of Mechanical and Aerospace EngineeringHong Kong University of Science and TechnologyKowloonChina
  3. 3.Ningbo UniversityNingboChina

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