Meeting Abstract

P3.19  Thursday, Jan. 6  The Energetic Cost of Stabilization in Cross Wind During Hovering in Hummingbirds CORDER, KR*; POWERS, DR; TOBALSKE, BW; George Fox University, Newberg, OR; George Fox University, Newberg, OR; University of Montana, Missoula, MT kcorder07@georgefox.edu

Recent studies have characterized the flight power curve for hummingbirds and elucidated the energetic costs of flying across a range of wind speed including 0 m/s (hovering). However no studies have addressed the energetic costs associated with body stabilization when ambient airflow includes crosswind components common in natural environments. To measure the contribution of stabilization to hovering metabolic rate (HMR) we placed a feeder in a wind tunnel that required calliope hummingbirds (Stellula calliope; n = 4) to hover feed with their longitudinal axis perpendicular to the direction of air flow (cross flow) and measured HMR using open-circuit mask-respirometry at 2, 4, and 6 m/s. HMR did not differ between cross wind speeds (mean = 0.48 + 0.12 mL O2 g^-1min^-1), but was significantly lower (1.5X) than HMR at 0 m/s and significantly higher (1.5X) than forward flight at 2, 4, and 6 m/s. During cross wind measurements hummingbirds rotated their posterior body away from the direction of airflow with the degree of rotation increasing with wind speed (21º at 2 m/s, 37º at 4 m/s, and 54º at 6 m/s). By rotating in this manner, hummingbirds oriented their wings such that it appeared incurrent airflow could reduce the induced power required for flight and, thereby, reduce HMR compared to hovering at 0 m/s. Because body rotation is incomplete, aerodynamic efficiency (lift : drag ratio) is likely less than that of forward flight making cross wind HMR more energetically expensive than forward flight at comparable wind speeds. Supported in part by NSF IOS-0923606 and IOS-0919799.