The Consequences of Reverse Sexual Size Dimorphism for Oxygen Consumption, Ventilation, and Water Loss in Relation to Ambient Temperature in the Prairie Falcon, Falco mexicanus

Abstract

The reversed sexual size dimorphism of prairie falcons is near the extreme found among raptorial birds. Mean basal metabolic rate (BMR) for males (390.2 ± 15.0 ml O₂/h) and females (504.8 ± 23.3 ml O₂/h) and mass-specific metabolism (0.79 ± 0.05 ml O₂/g h and 0.67 ± 0.03 ml O₂/g h, respectively) differ significantly between sexes. Females have a slightly broader thermal neutral zone (TNZ) than males; the upper critical temperature ($T_{uc}$) is ∼ 35 C for both sexes, and the lower critical temperature ($T_{lc}$) is 19 and 22 C, respectively. Below the $T_{lc}$ mass-specific rate of heat loss is the same in both sexes; the males' mean mass-specific conductance is 81% of the allometrically predicted value, and the females' is 86%. Mass-specific conductance of males diminishes more than that of females as ambient temperature ($T_{a}$) decreases. Mean tidal volumes and mean minute volumes ($\dot{V}_{I}$) are smaller in males than in females, but ventilatory patterns are similar for the sexes. Mean frequency a...