Differences in aggressiveness between brooded and non-brooded domestic chicks

Abstract

Eleven chick groups ( Gallus gallus domesticus) — seven with and four without a mother hen — were observed from hatching to 29–49 days of age. The strain used was the Old Swedish Bantam, which in many respects resembles the Red Junglefowl. The ontogeny of behaviour was studied and special interest was put on the development of aggressive behaviour and if the presence of a brooding hen had any influence on this. It was found that the frequency of aggressive behaviour during the period was higher in the non-brooded groups than in the brooded ones. The difference is significant for age classes from 15 to 45 days of age. A test on the correlation between the frequency of aggressive behaviour and the behaviour patterns most often preceding encounters gave no correlation in eight out of ten groups (one group was not possible to test because of its small value on aggression), although the “pre-encounter” activities were also found to be more frequent in the non-brooded groups. This result indicates that it is not only a higher general activity in the non-brooded groups that gives more aggressiveness, but that the hen specifically influences the aggressive motivation in her chicks. This might depend on a hypothetical super-dominance of the hen vis-à-vis the chicks. The duration of the encounters and the behaviour components involved also differed between the two categories; the mean duration was longer and there were components of actual fights in the non-brooded groups.