A population of Morpho rhodopteron (Godman & Salvin, 1880), one of the endemic and endangered butterflies of Colombia, was studied during a year in a sector of the northwestern part of the Sierra Nevada de Santa Marta. Mark-Release-Recapture methods were used to study population parameters and population size was estimated using the Jolly-Seber model. Environmental parameters of temperature and light intensity were measured for each capture event. We found abundance peaks in February, April and August that coincide with the first rains of the wet season, the stronger rains of the wet season, and the flowering season in the Sierra Nevada de Santa Marta respectively. Age structure was not stable, with an increase in young individuals from April to August. Residence times and population size were highest in February and April. Individuals flew mainly between 9:30 and 11:15 hours; when temperatures reached 25°C and the light intensity was between 20.000 and 30.000 Lux.