[The infradian rhythm in changes of thyroxine level and related periodicity of feather replacement during the molting in passerine birds].

In the course of 15 days, the thyroxine and corticosterone level was measured daily in blood serum of molting starlings, Sturnus vulgaris, by use of enzyme immunodetection method. Revealed are three-day rhythm in changes of thyroxine level and four-day one in changes of corticosterone level, both rhythms being synchronized in different birds. A beginning of growth of new oar feathers coincides with maximum thyroxine concentration in blood serum and also demonstrates a three-day period. In free-living passerine birds (Passer montamus, Parus major, Chloris chloris) a three-day rhythm is found in the dynamics of feather replacement. This rhythm is manifested synchronously in the studied species that differ in timing of post-nuptial molting. Established is the synchronous manifestation of three-day rhythm in changes of thyroxine level and feather replacement during molting in different passerine species and different birds of the same species.