Aerodynamics of owls during flapping flight; comparative study: great horned owl, tawny owl and boobook owl

Owls are known for silent flight during gliding and flapping thanks to their unique wing morphology. However, the current knowledge regarding their aerodynamic capabilities is incomplete. Here, we investigate owl’s aerodynamics; steady and unsteady contributions estimated from near wake flow measurements using long duration time resolved PIV. Three different owl’s species were flown in a wind tunnel in two flight configurations: perch-to-perch and steady flapping flight. Using long-time sampling data, several wingbeat cycles have been analyzed in order to cover both the downstroke and upstroke phases during flight. Drag and lift were obtained using the momentum equation for viscous flows and were found to share a highly unsteady behavior. The owls’ aerodynamics appeared to be different when comparing the two different flight modes over the two wingbeat phases. However, similarity was observed during transition phases. When comparing the flight performance of owls to other birds tested in the same facility, we found that the owls generate significantly more drag and less lift during steady flapping flight.