Supplemental File 4 weights from Hydration affects the physical and mechanical properties of baleen tissue

Baleen, an anisotropic oral filtering tissue found only in the mouth of mysticete whales and made solely of alpha-keratin, exhibits markedly differing physical and mechanical properties between dried or (as in life) hydrated states. On average baleen is 32.35% water by weight in North Atlantic right whales (<i>Eubalaena glacialis</i>) and 34.37% in bowhead whales (<i>Balaena mysticetus</i>). Baleen's wettability measured by water droplet contact angles shows that dried baleen is hydrophobic whereas hydrated baleen is highly hydrophilic. Three-point flexural bending tests of mechanical strength reveal that baleen is strong yet ductile. Dried baleen is brittle and shatters at about 20-30 N mm<sup>-2</sup> but hydrated baleen is less stiff; it bends with little force and absorbed water is squeezed out when force is applied. Maximum recorded stress was 4 times higher in dried (mean 14.29 N mm<sup>-2</sup>) versus hydrated (mean 3.69 N mm<sup>-2</sup>) baleen, and the flexural stiffness was >10 times higher in dried (mean 633 N mm<sup>-2</sup>) versus hydrated (mean 58 N mm<sup>-2</sup>) baleen. In addition to documenting hydration's powerful effects on baleen, this study indicates that baleen is far more pliant and malleable than commonly supposed, with implications for studies of baleen's structure and function as well as its susceptibility to oil or other hydrophobic pollutants.