The day draws to a close, and darkness surrounds the house. Occasionally lights are turned on, spilling pools of xanthic light about them, to be as suddenly and unpredictably turned off. The unnatural flickering glow of the television casts a ghostly pallor on everything in the room. Shadows appear and shift with chaotic frenzy. Finally, all are extinguished.
Darkness is the only consistent factor.
Consider these three scenarios. The first one of course, is the natural environment that most tropical birds experience. This is what their biological programming is tuned to make peak use of. Uncountable generations of birds have responded to the cues given by sunlight and atmosphere, and adjust their cycles of mating and nurturing, eating and play, rest and sleep, to coincide with the waxing and waning of the day. The second scene is far more common in the life of the captive bird.