Diving birds and wettability-tunable leaves

In this talk, I will discuss two problems in which mechanics principles affect form and function of animals or plants, as a result of evolutionary adaptations in nature. The first problem is how several seabirds (e.g. Gannets and Boobies) dive into water at up to 24 m/s without any injuries. This study examines the effects of their beak shape and dense feathers during water entry to reduce or spread the impact force on the body. We found that a specific beak and skull shape was chosen to minimize the water-entering force, and dense feathers also spread the impact too. The second problem is how tree leaves change their surface structure over season. In the fall, the wettability of Katsura leaves increases primarily due to the erosion of the second-tier (epicuticular wax) roughness features and the flattening of the first-tier (epidermal cells) surface features. Increased wettability during the fall may accelerate the leaf shedding processes by catching dew or rain droplets.