Fig. 3. Relationship between the equilibrium of ¹³C-labelled bicarbonate with varying amounts of CO₂. The enrichment values have been log-converted and plotted against the log-converted volume of CO₂ added in moles. The relationship was linear and significant (Regression; y=0.72–1.25x, F_1,31=7367.5, P<0.001). The equation for the relationship was used to calculate the size of the body bicarbonate pool (N_c) in moles and subsequently ml of CO₂ given a known isotope enrichment for each bird. See text for details.