Meeting Abstract

67.3  Thursday, Jan. 6  High evaporative water loss during endurance flight results in elevated lean mass catabolism in Swainson’s thrushes (Catharus ustulatus) GERSON, A.R.*; GUGLIELMO, C.G.; University of Western Ontario; University of Western Ontario agerson2@uwo.ca

Long distance migrant birds catabolize a mixture of lipids and protein during flight. Although many theories have been proposed, empirical evidence for the role of protein catabolism in endurance exercise remains unclear. For instance, protein may be utilized as a source of water during long distance flights since protein catabolism yields five times more endogenous water (0.155 g H2O/kJ) then the catabolism of lipids (0.029 g H2O/kJ). Therefore, the goal of this study was to determine if flight under dehydrating conditions results in elevated lean mass catabolism. Swainson’s thrushes (Catharus ustulatus) were flown in a wind tunnel at 18 ºC under conditions of high evaporative water loss (10% RH; HEWL) and low evaporative water loss (80% RH; LEWL). Each individual bird flew a minimum of two flights of matching duration, one under each condition. Flight order was determined randomly, and birds had a minimum of 4 days to recover from a previous flight. Flight duration ranged from 30 min to 5 h. Fuel mixture during flight was determined using plasma metabolites and by determining the changes in fat mass and lean mass during flight using quantitative magnetic resonance body composition analysis. Under HEWL conditions, birds utilized a fuel mixture with a higher proportion of lean mass and lower proportion of fat than under LEWL conditions. Flight costs as determined by the caloric value of the changes in body composition were similar. These data indicate that lean mass is preferentially catabolized during endurance flight under dehydrating conditions in a migratory bird, which could have functional consequences to flight performance or refueling time.