An infradian rhythm of changes in the thyroxine level and related periodicity in feather replacement during passerine bird molting

Abstract

The blood serum thyroxine and corticosterone levels of molting starlings (Sturnus vulgaris) were determined daily by enzyme immunoassay over 15 days. A 3-day rhythm for changes in the thyroxine content and a 4-day rhythm for corticosterone were observed, taking place synchronously in different individuals. The beginning of new flight feather growth coincided with maximal thyroxine concentration in the blood serum and also displayed a 3-day periodicity. A 3-day rhythm was also observed in the feather replacement dynamics of free-living passerines (Passer montanus, Parus major, and Chloris chloris). This rhythm was synchronous in the examined species, although they differed in the timing of their postnuptial molt. A synchronous manifestation of a 3-day rhythm of changes in the thyroxine level and feather replacement by molting in individuals of both the same and different passerine species has been observed.