Fig. 12
Plastic tube with a reference solution of saturated potassium chloride with an enclosed glass tube with a solution that increases in pH upon diffusion of hydrogen ions into the tube from the external aquatic environment. Electrodes record the electric potential between the two solutions (a) (adapted from [48]). A pH sensor used to record gastric pH and temperature within the stomachs of foraging emperor penguins (b) (taken from [48])