Cathemerality

Cathemerality, sometimes called "metaturnality", is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are undertaken.^[1] This activity differs from the generally monophasic pattern (sleeping once per day) of nocturnal and diurnal species as it is polyphasic (sleeping 4-6 times per day) and is approximately evenly distributed throughout the 24-hour cycle.^[2]

Many animals do not fit the traditional definitions of being strictly nocturnal, diurnal, or crepuscular, often driven by factors that include the availability of food, predation pressure, and variable ambient temperature.^[3] Although cathemerality is not as widely observed in individual species as diurnality or nocturnality, this activity pattern is seen across the mammal taxa, such as in lions, coyotes, and lemurs.^[4]

Cathemeral behaviour can also vary on a seasonal basis over an annual period by exhibiting periods of predominantly nocturnal behaviour and exhibiting periods of predominantly diurnal behaviour. For example, seasonal cathemerality has been described for the mongoose lemur (Eulemur mongoz) as activity that shifts from being predominantly diurnal to being predominantly nocturnal over a yearly cycle, but the common brown lemurs (Eulemur fulvus) have been observed as seasonally shifting from diurnal activity to cathemerality.^[5]

As research on cathemerality continues, many factors that have been identified as influencing whether or why an animal behaves cathemerally. Such factors include resource variation, food quality, photoperiodism, nocturnal luminosity, temperature, predator avoidance, and energetic constraints.^[6][7][8]