Drinking behavior and jaw muscle (EMG) activity in the pigeon (Columba livia).

The relation between jaw movements and jaw muscle activity was examined during two different types of drinking in pigeons: "tip" and "rictus" drinking. The amplitude and duration of jaw opening is greater for "rictus" than for "tip" drinking, but both types involve individual cycles of jaw-opening and closing movements, organized into bouts. Cycle duration increases gradually over the initial portion of the bout and is relatively constant thereafter. Each drinking cycle is composed of an initial rapid jaw-opening component, a sustained opening phase of variable duration and a closing movement. The initial and final phases are related, respectively, to activity in the upper beak levator (protractor) and the jaw closer (adductor, pterygoid) muscles. The amplitude and duration of the sustained phase are correlated with the magnitude and duration of activity in the lower jaw opener (depressor). The kinematic and electromyographic organization of jaw movements during drinking is discussed in relation to the morphology of the jaw apparatus and the functional requirements of the behavior.