Many creatures are photo-sensitive, and react strongly to changes in the light. Badgers, for instance, are almost entirely nocturnal: they rarely emerge from their sets before dusk, and are almost always below ground again around dawn. Foxes and owls also hunt mainly at night. Fallow deer emerge from the woods in the evening to feed on open fields, but as dawn breaks they head back to the safety of the trees.
In spring and autumn, lengthening or shortening daylight hours seem to have an influence on birds' migration, sending them off on their long journeys. It is thought that the pineal gland, in the front of the brain, produces more of the hormone melatonin at night than during the day, and that when the melatonin reaches a certain level, it triggers the migratory instinct.
Changing light also affects reproduction: chicken farmers manipulate the amount their birds receive so as to bring them to point-of-lay earlier.Reuse content