It was thought that spongy bone in woodpeckers’ heads cushioned their brains from onerous knocks, however actually their skulls are stiff like a hammer



Life



14 July 2022


Woodpeckers’ skulls aren’t constructed to soak up shock, however slightly to ship a more durable and extra environment friendly hit into wooden.

Woodpeckers hammer their beaks onto tree trunks to speak, to search for meals or to create a cavity for nesting. Spongy bone between the birds’ brains and beaks was as soon as thought to cushion their brains from the repetitive blows. However the tissue really helps their heads faucet swiftly and deeply with minimal vitality use, very like a well-designed hammer, says Sam Van Wassenbergh on the College of Antwerp in Belgium.

“We had a sense that this didn’t make any sense, this shock absorption [theory],” he says. “A hammer with shock absorption constructed into it’s merely a foul hammer.”

Van Wassenbergh and his colleagues analysed 109 high-speed movies of six captive birds as they hammered on wooden: two black woodpeckers (Dryocopus martius), two pileated woodpeckers (Dryocopus pileatus) and two nice noticed woodpeckers (Dendrocopos main).

They discovered that, within the milliseconds after a beak strike into the wooden, the birds’ eyes and heads slowed down at primarily the identical fee because the beaks did – which means that the spongy bone in entrance of the attention wasn’t compressing, nor absorbing, the results of the blow.

The staff then created digital fashions of pecking woodpeckers to check what would occur if the spongy bone did soak up shock. Whereas the cushioning would result in much less jarring for the mind, it additionally meant that the birds’ beaks couldn’t drive as deeply into the wooden, says Van Wassenbergh. In truth, with a purpose to get a deeper hit into the tree, the birds must work more durable with much more highly effective strikes of the top, in impact cancelling out any advantages of shock absorption.

Male pileated woodpecker

A male pileated woodpecker

Shutterstock/Mircea Costina

Regardless of the shortage of shock absorption, the staff discovered that the birds’ brains aren’t susceptible to a concussion as a result of the affect isn’t robust sufficient. Given the dimensions and weight of woodpecker brains, located inside fluid-filled circumstances of their skulls, they might solely maintain mind harm in the event that they pecked twice as quick as they naturally do, or in the event that they hit surfaces 4 instances more durable than their pure wooden targets.

“It’s simply regular {that a} smaller organism can stand up to these greater [forces],” says Van Wassenbergh, drawing a parallel with flies hitting home windows at even greater forces: “They only take off and fly once more.”

The time period “spongy bone” doesn’t imply that the bone is tender or can compress, he says. Fairly, it signifies that the bone is porous and light-weight – which is essential for flying birds. “The bone is simply robust sufficient for the perform that it must do,” he says.

Journal reference: Present Biology, DOI: 10.1016/j.cub.2022.05.052

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