Noun
photoperiod (plural photoperiods)
(biology) The normal duration of natural daylight experienced by an organism; daylength
Although not the only parameter, the changing length of the photoperiod ('daylength') is the most predictive environmental cue for the seasonal timing of physiology and behavior, most notably for timing of migration, hibernation, and reproduction. Source: Internet
Domestic dogs and certain small canids in captivity may come into oestrus more frequently, perhaps because the photoperiod stimulus breaks down under conditions of artificial lighting. Source: Internet
The sheep and goats exhibit remarkable seasonality of reproduction, in the determination of which the annual cycle of daily photoperiod plays a pivotal role. Source: Internet
It generally occurs during the spring and summer months, although some mares may be sexually receptive into the late fall, and is controlled by the photoperiod (length of the day), the cycle first triggered when the days begin to lengthen. Source: Internet