Fig. 5. Mean flight cost increases linearly with increased wing loading (diamonds); however, there were large variations in flight cost between flights in the same and different individuals and therefore the increase was not significant (GLM; F_4,65=0.11, P=0.98). The relationship for the mean flight cost was described by y=0.43x+16.63, r²=0.93. Adding a 10% body mass ventrally (square) had a lower flight cost than adding the same mass dorsally, but this was not significant (paired t-test; T=0.4, P=0.7).