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1. Ovarian development in Zonotrichia leucophrys gambelii subjected to long daily photoperiods is a logarithmic function of time until a weight of approximately 50 mg. is attained. Although there is a slight non-photoperiodic ovarian growth especially in first-year birds, it is clear that long daily photoperiods are essential for normal ovarian growth and constitute the basic environmental information used in the control of the ovarian cycle.2. The photoperiodic control mechanism in the female differs from that of the male in that the logarithmic growth phase brings the ovary to only approximately one-tenth of its maximum weight, whereas the logarithmic growth phase of the testes in photostimulated males brings them to about one half of maximum (See TABLE II in Source Pdf) weight. In addition, the female differs from the male in that complete gonadal development can be induced only rarely in captivity with either artificial or natural photoperiodic stimulation, whereas sufficiently long daily photoperiods...

The characteristics of the gonadal photoperiodic responses in the White-crowned Sparrow, Zonotrichia leucophrys gambelii, have been examined by the use of cyclic photoperiodic regimes consisting of a day with a long photoperiod followed by n days with short, non-stimulatory daily photoperiod, n with the range 0-5; responses measured were the rates of gonadal growth and the concentration of pituitary gonadotropin. The gonadotropic effect of a single 20-hour photoperiod extends through at least seven days with short (8-hour) non-stimulatory photoperiods. The apparently simplest interpretation of the results of the experiments suggests that there must be separate, although perhaps not completely independent, control schemes for synthesis and release of pituitary gonadotropin.