where FR is the current flow rate (ml min-1), F.IÖ2 is the incurrent broken O2 Concentration (0.2095) and F.eÖ2 is the ex-current fraction O2 Concentration. With everyone Ta, we measured resting values from V̇Ö2, WVP and Tb using the mean of the most stable 5 minute period of V̇Ö2. For each Tawe excluded data from birds that did not remain calm based on our observations of their behavior, which we later checked with our video recordings of the experiments. The birds were believed to be postabsorptive, as grumpy digested food within 1-2 hours (Gaston and Noble, 1985) and had fasted for 14.65 ± 1.4 hours in the chamber before our heat tolerance runs began. Hence convert V̇Ö2 for RMR (W) we have Eq. 9.13 used by Lighton (2019) to calculate energy equivalents (J ml-1 Ö2) assuming a respiratory quotient of 0.71 (Walsberg and Wolf, 1995). We calculated rates of EWL (mg min-1) by converting WVP (kPa) into water vapor density (mg ml-1) using the following equation from the Sable Systems Water Vapor Analyzer Manual, then multiply by the current flow rate:
where 461.5 (J kg K-1) is the individual gas constant for water vapor. To determine how efficient an individual murre was at dissipating heat, we calculated its evaporative cooling efficiency by converting EWL to EHL (W) assuming 2.406 J mg-1 H20, and divided by MHP, assuming that low EHL / MHP values indicate less ability to dissipate heat (Lasiewski et al., 1966).