Changes in food intake, body weight, gonads and plasma concentrations of thyroxine, luteinizing hormone and testosterone in captive male buntings exposed to natural daylengths at 29° N

Abstract

We have investigated the seasonal changes in food intake, body weight, gonadal volume and plasma concentrations of thyroxine, luteinizing hormone and testosterone in male blackheaded bunting (Emberiza melanocephala) in captivity under natural daylengths at 29° N. The cycles in food intake, body weight and testis size in buntings appeared to be phase related. While the changes in body weight and testicular size were parallel to each other and correspond to the increasing daylengths of spring and early summer, cycle in food intake was almost antiphase to the cycles in body weight and testicular growth and development. Furthermore, buntings showed a distinct seasonal cycle in plasma concentrations of thyroxine, luteinizing hormone and testosterone. It is suggested that these seasonal cycles in buntings are endogenously programmed and their entrainment to the environmental photoperiod ensures the occurrence of different physiological functions at temporally fixed time of the year.