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Science 16 May 2008:
Vol. 320. no. 5878, pp. 931 - 934
DOI: 10.1126/science.1156023
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Reports

Surface Tension Transport of Prey by Feeding Shorebirds: The Capillary Ratchet

Manu Prakash,1 David Quéré,2 John W. M. Bush3

The variability of bird beak morphology reflects diverse foraging strategies. One such feeding mechanism in shorebirds involves surface tension–induced transport of prey in millimetric droplets: By repeatedly opening and closing its beak in a tweezering motion, the bird moves the drop from the tip of its beak to its mouth in a stepwise ratcheting fashion. We have analyzed the subtle physical mechanism responsible for drop transport and demonstrated experimentally that the beak geometry and the dynamics of tweezering may be tuned to optimize transport efficiency. We also highlight the critical dependence of the capillary ratchet on the beak's wetting properties, thus making clear the vulnerability of capillary feeders to surface pollutants.

1 Center for Bits and Atoms, Massachusetts Institute of Technology (MIT), 20 Ames Street, Cambridge, MA 02139, USA.
2 Physique et Mécanique des Milieux Hétérogènes, UMR 7636 du CNRS, Ecole Supérieure de Physique et de Chimie Industrielles, 10 rue Vauquelin, 75005 Paris, France.
3 Department of Mathematics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)