Activity Periods of Indonesian Rain Forest Mammals

Activity periods of rain forest animals, especially those with flexible activity periods, are poorly known. .We used camera trapping to describe the activity periods of at least partly terrestrial wildlife in 2 Sumatran and 1 Javan rain forest sites. We used these data and a comparison with the literature to classify all mammalian taxa occurring in the study areas as either diurnal, nocturnal, or cathemeral (potentially active during both day and night). Exploratory analyses revealed that body size and substrate are the major correlates of activity period, with diet and travel mode playing minor roles. We explain the substrate effect by noting that vision-related constraints force diurnal mammals in an arboreal environment to stay diurnal regardless of conditions, and that nocturnal mammals are kept from becoming diurnal by predation risk by visually hunting diurnal predators. To explain why the largest animals are cathemeral we suggest that they require more time to forage than is provided by the roughly 12-hour diurnal or nocturnal period.