TONIC IMMOBILITY AND HIGH-INTENSITY CALLS IN A PRECOCIAL CHICK AS A FUNCTION OF AGE, DIET, AND TIME OF DAY

Tonic immobility (TI) and high-intensity vocalizations are two antipre dator behaviors employed by domestic chicks (Gallus gallus) which vary in their function and the proximate mechanisms that govern them. In t he present study, we sought to determine the influence of age (3 or 10 days old), diet (control or tryptophan-free), and time of testing (A. M. or P.M.) On the duration of TI and the number of calls produced in domestic chicks. Older chicks remained immobile significantly longer t han younger chicks as did subjects on the control diet or those tested at night. However, 3-day-old chicks had significantly shorter TI dura tions only when tested in the A.M.: TI did not differ between age grou ps when subjects were tested in the P.M. Three-day-olds called signifi cantly more than 10-day-olds when given the control diet and when test ed in the P.M. but vocalization frequencies did not differ between age groups during the A.M. testing or when given the tryptophan-free diet (T-). Vocalization rate (calls/TI duration), however, was significant ly greater during the A.M. testing. These results emphasize the import ance of considering circadian rhythms and behavioral development. Furt hermore, an integrative view of the proximate mechanisms and adaptive functions of TI and high-intensity vocalizations is presented. (C) 199 4 John Wiley & Sons, Inc.