Biological clocks, internal molecular machines that keep track of time within organisms, and circadian rhythms, which keep track of the 24-hour cycle of day and night and light and dark, both enable organisms to adapt their behavior according to the most suitable conditions. There are many selective advantages that go along with the biological clocks of organisms, allowing them to be more productive, reproduce more easily, and mature in the most favorable conditions. These internal clocks help to ensure the evolutionary success of a creature within its habitat or environment during the most favorable conditions. .
Plants are more plentiful in the summer due to increased sunlight, growing more than they do in any other reason. Animals often hunt of forage for food in the daylight, especially during the summer, when food is the most plentiful and grows the best. It is their internal clocks that tell them to begin to gather the food needed, not only for that season but also for seasons ahead, when food will not be as readily available.
This makes different creatures more able to survive the harsh winters that may follow.
The habit of sleeping during the colder, darker period of winter is known as hibernation and is regulated by a biological clock within many organisms. Instead of migrating long distances to a better climate or source of winter food, hibernating animals typically respond to local conditions by finding a safe, well-insulated dwelling and then altering their behavior, lowering metabolisms and sleeping all winter. Hibernation is a well-regulated strategy to counter food shortages and increased energy demands during winter. Internal signals help an organism know when to end is period of hibernation and return to normal functioning.
Often animals have seasonal mating period timed so that the young are born within the late spring to early summer, when food is most abundant.