Cathemeral Activity of Red-Fronted Brown Lemurs (Eulemur Fulvus Rufus) in the Kirindy Forest/CFPF

Abstract

Cathemeral activity, which is defined by sequences of activity bouts and resting phases throughout the 24 hour cycle, is rare among primates but common among group-living lemurs. The proximate and ultimate causes and mechanisms underlying this activity pattern are still obscure. One group of Red-fronted Brown Lemurs(Eulemur fulvus rufus)was therefore observed in Kirindy Forest/CFPF for a total of 384 hours between March and June 1996 to investigate potential causes and correlates of their activity. Observations were equally distributed between diurnal and nocturnal activity cycles and intensified around periods of full and new moon. We found that Kirindy Red-fronted Brown Lemurs exhibited cathemeral activity throughout the study period and documented a significant increase of nocturnal and a concomitant decrease of diurnal activity during the transition between the wet and dry season (i.e., in April---May). Intensity and duration of activity were dependent upon lunar phase, due to a significant increase in activity during the nights of full moon. Furthermore, a balance between diurnal and nocturnal activity levels was observed. The animals moved on average 989 m during the day and 749 m at night within their 20.5 ha home-range. Distance traveled at night increased significantly during the dry season and nocturnal activity was also negatively correlated with minimum temperature. Red-fronted Brown Lemurs and their feeding patches were located significantly higher above ground at night. Considering that during the dry season less cover is provided by vegetation, these results suggest that the animals avoided diurnal exposure in the canopy and compensated for it with an increase of nocturnal foraging, especially during a full moon. Minimizing predation risks and thermoregulation benefits may therefore be among the main determinants of this behavioral strategy.