Fig. 4. Changes in mean hourly pH of the stomach contents of seven male king penguins (birds 1–7) during the first week of their incubation fast. Daily and minimum mean values found for control birds are indicated by broken and dotted lines, respectively. Absence (–) or presence (+) of bile pigment coloration in the food is indicated at the beginning and the end of the period studied. Values are means ± S.D.