The river at night: nocturnal foraging of the Amazonian manatee on the riverside plant maracarãna (polygonaceae)

Abstract Animals adopt various behavioral strategies to meet their biological needs, often adjusting their activity cycles. While some species restrict their activities to specific periods within the 24-hour light and dark cycle, others are cathemeral, showing flexible activity patterns that include both day and night. This study investigates the cathemeral activity of Amazonian manatees ( Trichechus inunguis ) in Anavilhanas National Park, Brazil, with a focus on their nocturnal behavior and ecological adaptability. Using thermal cameras, we recorded nocturnal feeding for the first time, highlighting the manatees’ flexibility beyond the typical diurnal–nocturnal cycle. Our findings reveal that manatees adjust their feeding strategies according to seasonal vegetation availability and water levels. Specifically, they feed at night on the riparian plant maracarãna ( Coccoloba densifrons ), which is only accessible during the flood season. This nocturnal behavior likely helps minimize predation risk and enhances foraging efficiency. These insights significantly improve our understanding of manatee ecological behavior in the Amazon, demonstrating their adaptability to environmental changes. The study underscores the importance of considering cathemeral activity in conservation strategies to ensure the ongoing protection of Amazonian manatees against environmental and human pressures.