Diurnality is a plant or animal behavior characterized by activity during the day, with a period of sleeping, or other inactivity, at night. The common adjective used for daytime activity is "diurnal". The timing of activity by an animal depends on a variety of environmental factors such as the temperature, the ability to gather food by sight, the risk of predation, and many others. Different behaviors may occur at different times of year; diurnality is a cycle of activity with a twenty-four-hour period while other cyclic activities are described as circadian rhythms. Animals active at dawn or dusk are described as crepuscularwhile those active at night are nocturnal. Some animals, such as those living underground, may be active at any time of day or night.

Plants that open their flowers during the day are referred to as diurnal, while those that bloom at night are nocturnal. The timing of flower opening is related to the time at which insects and other pollinators are foraging. Some trees are pollinated by bats and these open their flowers at night; the baobab does this, and their flowers open in the afternoon and live for a single night.

In animals

Animals that are not diurnal might be nocturnal (active at night) or crepuscular (active primarily during twilight, i.e., at dusk and dawn). Many animal species are diurnal, including many mammals (including humans), insects, reptiles and birds. In some animals, especially insects, external patterns of the environment control the activity (exogenousrhythms, as opposed to patterns inherent in the habitat). Diurnality is descriptive; it refers to an observed 24-hour pattern, as opposed to ~24-hour circadian rhythms which are self-sustaining within the organism.

In many species, the animal switches from nocturnal to diurnal foraging depending on the environmental temperature. The reason for the switch allows the individual to maximize on feeding efficiency during summer time when it is warmer and lower their risk of predation during the winter. Diurnal insect include some bees and a specific example being the bee species Anthidium maculosum. These carder bees are diurnal and are active only when the temperatures are above freezing. Moreover, these bees are most active when there are plenty of resources such as flowers, from which they can extract pollen and nectar.

Some mainly nocturnal or crepuscular animals have been domesticated as pets and have changed into diurnal animals to coincide with the cycle of human life. Examples are pet dogs and cats. However, these animals may exhibit their species' original behavior when they are born feral. Other animals have been forced from their normal cycle to an alternate one as a means of avoiding predators, such as beavers becoming nocturnal creatures after extended predation by humans.

In plants

Many plants are also diurnal or nocturnal, depending on the time period when the most effective pollinators, i.e., insects, visit the plant. For example, as most angiosperm species of flower are visited by many various insects, the flower adapts its phenology to the most effective pollinators. Thus, the effectiveness of relative diurnal or nocturnal species of insects affects the diurnal or nocturnal nature of the plants they pollinate, causing in some instances an adjustment of the opening and closing cycles of the plants. The baobab is pollinated by fruit bats and it starts blooming in late afternoon and the flowers are dead within twenty-four hours.

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