Figure 1. Effect of photostimulation on follicle growth in captive great tits in winter.

Follicle length (A) and volume (B) of the three experimental groups in the aviary experiment before and one month after the photostimulation. All birds were kept in an outdoor aviary and only moved indoor for the photostimulation treatment. Of the females of which we successfully measured the largest follicle in December and January, two birds were kept under natural light conditions (solid lines), 3 individuals were given one long day (dashed lines) and 4 individuals were given two long days (seven days apart; dotted lines).