Its really a sound wave pulsing through the grey mush of each brain, so some measure of stress (force/area) or strain (differential displacement/area) might be the beast way to look at it. The damage might be done in shear where the center of the brain moves while the outside is stuck to the skull, but it would be really hard to measure that.
Maybe woodpecker brains are more free to wobble around inside their skulls so shear stresses and strains are lower than they are in people?
Maybe woodpecker brains are more free to wobble around inside their skulls so shear stresses and strains are lower than they are in people?