Ontogeny of the ultradian rhythm of activity in Japanese quail

As soon as they hatch, gallinaccous chicks follow broody hens. This matriar chal unit presents a temporal organization of activity. The ontogeny of thi s ultradian rhythm of activity was followed in Japanese quail during their first 3 weeks of life. Under controlled laboratory conditions, 12 groups of four chicks were recorded using an activity monitoring system. They were o bserved between the ages of 3 and 17 days. Chicks in groups presented an ul tradian rhythm of activity, with a period that increased significantly from 14.3 +/- 1.4 minutes when chicks were 2 days old to 26.0 +/- 1.9 minutes w hen they were 16 days old. The increase of ultradian periodicity was partic ularly pronounced during their first and third weeks of life. Finally, the ultradian period was correlated positively with body weight of the chicks.