Sexual development and free-running period in quail kept in constant darkness

In Japanese quail (Coturnix coturnix japonica) sexual development may occur in total darkness (DD). Linked to sexual maturation, variations of the rhythm of feeding activity were observed: in DD, the amount of activity increased and the period of the free-running rhythm lengthened. During the first weeks in DD all the quails presented a free-running period less than 24 hr (22.3 +/- 0.5 hr; N = 50). At the end of the experiment, the more a bird was mature, the greater the lengthening of its period. In DD, testosterone implants in castrated male quails can mimic these modifications but we failed to find any correlation between the number of implants (i.e., the level of testosterone) and the extent of the lengthening.