Western and Clark's grebes use novel strategies for running on water

Few vertebrates run on water. The largest animals to accomplish this feat are Western and Clark’s grebes (Aechmophorus occidentalis and clarkii). These birds use water running to secure a mate during a display called rushing. Grebes weigh an order of magnitude more than the next largest water runners, basilisk lizards (B. basiliscus), and therefore face a greater challenge to support their body weight. How do these birds produce the hydrodynamic forces necessary to overcome gravity and sustain rushing? We present the first quantitative study of water running by grebes. High-speed video recordings elucidate the hindlimb movements of grebes rushing in the wild. We complement these findings with laboratory experiments using physical models and a preserved grebe foot to estimate how slapping the water surface contributes to weight support. Our results indicate that grebes employ three novel tactics to successfully run on water. First, rushing grebes use exceptionally high stride rates, reaching 10 Hz. Second, grebe foot size and high water impact speed allow grebes to generate up to 30-55% of the required weight support through water slap alone. Lastly, flattened foot bones reduce downward drag, permitting grebes to retract each foot from the water laterally. Together, these mechanisms outline a water running strategy qualitatively different from that of the only previously-studied water runner, the basilisk lizard. The hydrodynamic specializations of rushing grebes could inform the design of biomimetic appendages. Furthermore, the mechanisms underlying this impressive display demonstrate that evolution can dramatically alter performance under sexual selectionOrganismic and Evolutionary Biolog

Replication Data for: Foot-propelled swimming kinematics and turning strategies in common loons

Data associated with the paper "Foot-propelled swimming kinematics and turning strategies in common loons" published in the Journal of Experimental Biology (2018)

Constant speed gaits should work across all speeds

This is a 1-page peer reviewed extended abstract for a talk presented at Dynamic Walking 2021The Stokesian form of the reconstruction equation of Geometric Mechanics arises when the contact forces are so large compared to body inertia that the group momentum decays almost instantaneously. As special case of this occurs when body velocity is constant. In that case it can be shown that for a variety of types of contact friction, as long as all contacts use the same type of friction, time-rescaling the body shape change would produce a geometrically identical motion at a re-scaled speed. The implication of this observation is that if an animal or robot managed to discover a pattern of shape-changes which produces a constant velocity motion, that pattern could be used for every speed. The limiting factor would not be interaction with the environment -- it would be the ability of the body to change its own shape at the desired rates.Army Research Office Defense University Research Instrumentation Program grant W911NF-17-1-0243Army Research Office Multi University Research Initiative grant W911NF-17-1-0306National Science Foundation Civil, Mechanical and Manufacturing Innovation grant 1825918D. Dan and Betty Kahn Michigan-Israel Partnership for Research and Education Autonomous Systems Mega-ProjectPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172174/1/DW2021-2.pdf84b631d7-aa77-4c16-b024-4ad83d186b3cDescription of DW2021-2.pdf : Main documentSEL

Bridging Walking and Slithering – Stokesian Locomotion

This a peer reviewed 1-page extended abstract for a talk given at the Dynamic Walking conference, 2021Both legged locomotion and slithering motions typically utilize periodic gaits – repeating cycles of body shape change that produce a net motion through the world. Legged locomotion can be viewed from the perspective of piecewise contact constraint formation and removal. Slithering and low Reynolds number swimming operate under continuous constraints of force balance, wherein dissipation removes the ability to accumulate momentum. Here we discuss how to bridge the gap between these domains of motion, thereby, among other benefits, producing models for the space of legged locomotion with slipping. The connective fabric is the use of a “Stokesian”, or “local connection” model.Army Research Office Defense University Research Instrumentation Program grant W911NF-17-1-0243 Army Research Office Multi University Research Initiative grant W911NF-17-1-0306 National Science Foundation Civil, Mechanical and Manufacturing Innovation grant 1825918 D. Dan and Betty Kahn Michigan-Israel Partnership for Research and Education Autonomous Systems Mega-ProjectPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172173/1/DW2021-1.pdf84b631d7-aa77-4c16-b024-4ad83d186b3cDescription of DW2021-1.pdf : Main documentSEL