Why Don't Woodpecker Beaks Get Stuck in Trees?

Have you ever wondered how woodpeckers are able to peck into trees repeatedly, furiously searching for food, without getting their beaks stuck? I haven't really either but a team of researchers at the University of Antwerp in Belgium were very interested in the answer.

The research team already knew that woodpeckers hammer their beaks into wood, not any different than us hammering a nail, but they figured there must be something unique going on in the process.

To get to the bottom of this strange process, the team used a high-definition, high-frame-rate camera from Mikrotron, specifically the Mikrotron 1.3 mp recording camera which creates slow-motion, high-resolution videos for kinematics analysis.

First, let's understand what happens with a normal nail being hammered. A process called deformation occurs whenever a sharp object penetrates a softer, porous, and fibrous tissue such as wood. When this happens, the wood clamps around the object which then creates shear forces that resist against the object being pulled back. So if you apply this to a woodpecker's beak, it would be assumed that it heavily affects and compromises its performance to forage for its breakfast.

For their study, the research team recorded high-speed videos of black woodpeckers (Dryocopus martius) in lateral view during pecking with the Mikrotron cameras set in an uncompressed 10-bit monochrome format.

One of the woodpeckers was filmed while pecking wood at a video frame rate of 500 frames per second and a resolution of 1280 x 1024 pixels. A second woodpecker was filmed at 1533 frames per second and 704 x 564 pixels. Out of many videos created, 10 beak retraction events were selected for in-depth analysis based on view perspective and image sharpness. Pixel coordinates of eight anatomical landmarks were tracked frame-by-frame with either XMAlab 1.5.5 or Progressive Tracker software.

Kinematic video analysis of the black woodpeckers showed how they manage to quickly withdraw their beaks, revealing a two-phase pattern. First, a few degrees of beak-tip-down rotation about the nasofrontal hinge causes the tip of the upper beak to be retruded while its proximal end is lifted. Next, the head is lifted, causing beak-tip-up rotation about the nasofrontal hinge while the lower beak starts retruding and initiates the final freeing.

The team concluded that these consecutive actions facilitate beak retraction by exploiting the likely low frictional resistance between the upper and lower beak surfaces, allowing them to slide past each other. It also demonstrates the counter-intuitive value of maintaining cranial kinesis (the ability to move the upper beak relative to the brain and skull) in a species adapted to deliver forceful impacts. This suggests that efficiently dealing with stuck beaks is important for the successful execution of bouts of short-interval pecks, normally about 20 pecks per second. During this process, the woodpeckers make extensive use of cranial kinesis.

By using Mikrotron's camera, the University of Antwerp researchers were able to quantify the kinematics of a previously unknown behavior exhibited by black woodpeckers. So, how do woodpeckers avoid getting their beaks stuck in wood? Simply by the fact that they can quickly retract their upper and lower beaks in quick succession, facilitating the release of their beaks. Or in plain terms, once they peck into wood, before pulling out they open their beaks to create more room to pull them out.

For more information, visit www.svs-vistek.com or www.mikrotron.de. Mikrotron is a brand of SVS-Vistek.