Fig. 8. (A) Bilateral vagotomy did not eliminate body temperature (T_b) depression in response to stepwise hypoxia. Vagotomized ducks exposed to hypoxia (black and white circles) began reducing T_b during 9% inspired O₂ (black arrow), and reached lower mean T_b than intact ducks (dark grey circles). (B) Bilateral vagotomy abolished the increase in bill surface temperature that occurs in intact ducks during hypoxia. Vagotomized ducks kept in normoxia for equivalent durations (white circles) did not alter T_b or bill temperature; data for these controls are only shown at the end of each 15 min period for clarity.