Meeting Abstract

97.3  Wednesday, Jan. 7  Respiratory Evaporative Water Loss During Hovering Flight in Hummingbirds POWERS, DR*; GETSINGER, PW; WETHINGTON, SM; TOBALSKE, BW; George Fox University, Newberg, OR; George Fox University, Newberg, OR; Hummingbird Monitoring Network, Patagonia, AZ; University of Montana, Missoula, MT dpowers@georgefox.edu

Evaporation of water across body surfaces is an important method for heat dissipation in vertebrates. Hummingbirds (family Trochilidae) are among the smallest vertebrate endotherms resulting in extremely high rates of metabolism evaporative water loss (EWL). High rates of EWL contribute to water turnover rates that are as much as 5X their body mass. In this study, we made the first respiratory evaporative water loss (REWL) measurements for free-living hummingbirds during unencumbered hover flight. Measurements were made on 6 species ranging in mass from 3-8 g to determine the impact of REWL on their daily heat and water budgets. All measurements were obtained using a negative-pressure, open-flow respirometry system attached to a drip-free feeder at which the birds hover fed. REWL ranged from 80-150 mg g^-1h^-1 (8-15% of body mass) which is 50 times higher than REWL measured in resting birds, and 2-15 times higher than that measured in other birds during forward flight. Heat dissipated by REWL is about 0.36 kJ g^-1h^-1 which is about 35% of their hovering metabolic rate. Thus, REWL is a notable contributor to water turnover and heat dissipation during hovering in hummingbirds. Since hovering is the most energetically expensive activity for hummingbirds, these data further our understanding of water and heat budget management by a tiny endotherm during intense activity. Supported in part by NSF IOB-0615648.