Woodpecker Pecking Drew AltschulWhy it is that woodpeckers do not get brain injury from pecking? • People get brain injury if the brain decelerates at about 100g over about 5 millisecond (the time of a typical impact in a car crash) • Measurements on woodpeckers indicate that they tolerate decelerations of up to 1500g over about 0.5 milliseconds during pecking • (g is the acceleration of gravity) (millisecond = 1/1000 second) May PRA Fuster JM, Habe J and Hirschman A (1979)Woodpecker Drilling Behavior Arch Nerol 36, 370-373Woodpecker Pecking • High speed video images taken at 2000 frames per second • Get one image every 0.5 milliseconds • Declerations of 600-1500g during impact May PRA Fuster JM, Habe J and Hirschman A (1979)Arch Nerol 36, 370-373Scaling • The stress on the brain in an impact is the force/area • The force is the brain mass times the deceleration stress = force area = mass  deceleration areaScaling • Assuming that the brain tissue of humans and woodpeckers can tolerate the same stress: mhdh mwdw = Ah Aw • m = mass h = human • d = deceleration w = woodpecker • A = area = r2Scaling • Rearranging, dw = mh mw Aw Ah dh = mh mw rw 2 rh 2 dh • m = mass h = human • d = deceleration w = woodpecker • A = area = r2Scaling mh = 1400 grams rh = 60mm mw = 2 grams rw = 7mm giving: dw ~10 dh The woodpecker brain can withstand about 10 times the deceleration that a human brain can. Photos of human head and woodpecker head, showing relative size, removed for copyright reasons.Scaling • The deceleration that the human brain can tolerate depends on the duration of the deceleration: Goldsmith W (2001) The state of head injury biomechanics: past, present and future: Part 1 Critical Reviews in Biomedical Engineering 29, 441-600.Scaling • The duration of the woodpecker deceleration during pecking has been measured to be 0.5 milliseconds • For this duration, the human brain can withstand about 500g deceleration • The woodpecker can withstand about 10 times this, or 5000g • Maximum measured decelerations of 1500g are well below