  This study explores the impact of feathers on the hydrodynamic drag
experienced by diving birds, which is critical to their foraging efficiency and
survival. Employing a novel experimental approach, we analyzed the kinematics
of both feathered and non-feathered projectiles during their transition from
air to water using high-speed imaging and an onboard accelerometer. The drag
coefficients were determined through two methods: a direct calculation from the
acceleration data and a theoretical approach fitted to the observed velocity
profiles. Our results indicate that feathers significantly increase the drag
force during water entry, with feathered projectiles exhibiting approximately
double the drag coefficient of their smooth counterparts. These findings
provide new insights into the role of avian feather morphology in diving
mechanics and have potential implications for the design of bio-inspired
aquatic vehicles in engineering. The study also discusses the biological
implications of increased drag due to feathers and suggests that factors such
as body shape might play a more critical role in the diving capabilities of
birds than previously understood.
