Fig. 2. The calibration if the ¹³C-labelled bicarbonate technique in cockatiels 20–30 min after injection. (A) There was no significant relationship if isotope elimination rate (k_c) alone is used for the comparison with the metabolism (_O2) measured simultaneously by indirect calorimetry (regression; y=10.6x+3.8, r²=0.11, F_1,20=2.35, P=0.14) with a low r² of 10.99%. (B) The relationship of oxygen consumption to the product of elimination rate and bicarbonate pool size was significant (regression; y=5.12x+0.3, r²=0.72, F_1,20=49.54, P<0.001) with a high r² of 72.3%.