Light affects reproduction in birds in two ways. First, there is a photoperiodic mechanism
that, in nature, determines the onset and (in some cases) the termination of seasonal
breeding at temperate latitudes. Second, there is what can be referred to as a "biological
clock", which controls the timing of egg laying on any given day. In short, light affects
the rate of sexual maturation (age at first breeding) and the rate of egg/sperm production
(duration of the breeding season).