diurnally

Diurnally is an adverb meaning during the day or daytime. It is used to describe actions, patterns, or phenomena that occur within daylight hours. The term derives from Latin diurnus, meaning of the day, which itself comes from dies, day.

In biology, diurnal describes organisms that are active during daylight and rest at night. Humans are typically diurnal, as are many birds, primates, and numerous insects. Diurnality is influenced by circadian clocks and environmental cues such as light. Some species are strictly diurnal, while others show flexible patterns, being diurnal under certain conditions or life stages. The term helps differentiate daytime activity from nocturnal (night-active) and crepuscular (active at dawn and dusk) patterns, as well as from cathemeral activity, which can occur irregularly across day and night.

Diurnal also appears in broader scientific contexts to denote daily cycles or variations. For example, diurnal temperature variation describes the typical rise and fall of temperature within a 24-hour period, and diurnal plant processes may involve daily rhythms in photosynthesis or stomatal conductance. The concept is frequently used in ecology, meteorology, and chronobiology to summarize how day-night cycles shape behavior and environmental change.

See also: nocturnal, crepuscular, cathemeral, circadian rhythm.