Progesterone in male white-crowned sparrows, Zonotrichia leucophrys gambelii

Abstract

During the course of a photoperiodically induced cycle of testicular growth and regression in Zonotrichia leucophrys gambelii the concentration of progesterone in plasma was found to range from about 400 to about 1000 pg/ml but was at no time significantly different from that of controls held on constant short days (8L 16D). There were no apparent correlations between its concentration and those of luteinizing hormone, testosterone, or dihydrotestosterone, or with the phase of development of the testes, or with the onset of molt. The plasma levels of progesterone of four castrated males were within the ranges of those of the photostimulated birds and of the short-day controls, suggesting that at least the major source of plasma progesterone is extratesticular.