Elastic feathers spreading fluid-impact force*

Northern Gannets are seabirds that frequently employ a hunting tactic called ‘plunge-diving’ in which they dive through the water surface at high-speeds to catch underwater prey; often reaching speeds of up to 24 m/s at the moment of impact. It can result in forces as high as 500 N acting on the bird’s neck during impact, yet the bird escapes uninjured, despite making 20-100 dives per foraging trips. However, little is known about how such high impact forces affect the rest of the body. The goal of this study is to investigate the role played by the feathers in spreading the hydrodynamic forces on the skin around the impact zone. We model the feathers as elastic beams taking into account their pre-curvature and non-uniform cross-section. Results from our experiments with polycarbonate beams suggest that the interaction of feathers on the skin patch redistributes the force, thereby reducing the impact on any particular area of the skin.