DRINKING BEHAVIOR AND JAW MUSCLE (EMG) ACTIVITY IN THE PIGEON (COLUMBA-LIVIA)

The relation between jaw movements and jaw muscle activity was examine d during two different types of drinking in pigeons: ''tip'' and ''ric tus'' drinking. The amplitude and duration of jaw opening is greater f or ''rictus'' than for ''tip'' drinking, but both types involve indivi dual cycles of jaw-opening and closing movements, organized into bouts . Cycle duration increases gradually over the initial portion of the b out and is relatively constant thereafter. Each drinking cycle is comp osed of an initial rapid jaw-opening component, a sustained opening ph ase of variable duration and a closing movement. The initial and final phases are related, respectively, to activity in the upper beak levat or (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 jam opener (depressor) . The kinematic and electromyographic organization of jaw movements du ring drinking is discussed in relation to the morphology of the jaw ap paratus and the functional requirements of the behavior.