Understanding the activity pattern of animals is important for both ecological knowledge and species conservation. Here we present a quantitative analysis of the activity pattern of the Boat-billed Heron (Cochlearius cochlearius) in the eastern Brazilian Amazon. Activity patterns were determined using images from 2,822 camera trap days distributed across 19 sites along waterways during two years (2018-2019). To test if the Boat-billed Heron was more active during darker nights we also evaluated the nocturnal photos of the species as a function of the degree of lunar illumination. Our sampling effort resulted in 22 independent records, consisting mostly of nocturnal records (63.6%), followed by dusk (27.3%), and dawn activity (9.1%), with no records registered during the day. We found significant differences between the observed and expected activity of the species, while comparing records with and without the moon apparent in the sky. The species seemed to be active during both darker and brighter nights, showing no clear trend in relation to the moon fraction illumination in our study area. Our findings highlight the ecological plasticity of the Boat-billed Heron, which has a key function in the maintenance of the species within its distributional range.