Figure 1.

Seasonal changes in (a) paired testis mass (mg) and (b) largest ovarian follicle diameter (mm) in male and female European starlings (Sturnus vulgaris), respectively, collected each month from March 1994 to February 1995 in Baltimore, MD, USA. Points represent mean±s.e. of the mean. Points with different letters differ significantly, while points with the same letter do not. Note how similar the relative pattern of change is in these field-caught male and female starlings. Male starlings, like many other temperate zone songbird species, when held in captivity under artificial photoperiods exhibit changes of a similar magnitude to that observed in the field. In contrast, captive female starlings exhibit a change of a much smaller magnitude.