Causal Factors Controlling the Brooding Cycle of Broody Junglefowl Hens with Chicks

Abstract

This study was designed to find evidence for the causal factors responsible for the length of the brooding cycle (brooding, preening, feeding, exploring, dustbathing, and then brooding again) of broody hens with chicks. In part I, we examined brooding and non-brooding behaviors during the first 8 days after the chicks hatched. Eight groups of birds were monitored continuously during the 14-h daily light period with a time-lapse video recorder. The amount of time spent brooding per cycle declined over days, while the amount of time spent in other activities increased. Nonetheless, the total cycle length remained approximately constant at about half an hour between days 3 and 7. Correlations between brooding and non-brooding within cycles were small, but positive, as were correlations between successive brooding cycles. Frequency distributions of cycle length showed large variability both within and between hens. Autocorrelation functions provided evidence of significant periodicity in brooding behavior, but the periods also varied greatly both from day to day and between hens. These results all suggested that an ultradian clock was not responsible for the observed constancy in cycle length over days. In part II, 18 broody hens with chicks were deprived of dust from day 6 to day 8. Deprivation of dust per se had only small effects on the behavior of the hens. Reintroduction of dust on day 8, however, led to immediate, sustained dustbathing by all hens, which affected the length of the brooding cycle and the sequence of behaviors within a cycle. These results were interpreted as a reflection of competition between behavior systems, although the existence of an ultradian clock could not be ruled out.