Abstract
We examined seasonal changes of the gonadal glands (testes and ovaries) of Jungle Crows C. macrorhynchos living in the Kanto area, Japan. Adult (male: N=50, female: N=32) and juvenile (male: N=66, female: N=34) Jungle Crows were trapped between October 2003 and September 2004. In April and May, weights of testes, weights of ovaries and diameters of largest follicles in adult crows were greater than during other seasons. No juvenile crows had enlarged testes or ovaries with well-developed follicles as in adult crows, thus they seemed to be sexually immature. However, gonadal sizes were also greater in April and May in juvenile crows than during other seasons. Juvenile crows may respond to some environmental stimuli, such as changes in photoperiod, that signal the onset of the reproductive season even when still sexually immature.
