The present study focuses on how resource variability in forests affects species diet, using the guacharo as a model to explore differences between colonies located at different altitudinal levels. The oilbird (Steatornis caripensis) is a nocturnal frugivorous bird that inhabits neotropical forests and plays a key role as a seed disperser due to its high mobility capacity. Here, I investigated how the diet of the oilbirds varies among colonies located at two different altitudes. To answer this question, I studied the diet in three colonies in the department of Santander: two in El Peñón (2600 m.a.s.l) and one in Bolívar (1600 m.a.s.l.). I placed six seed traps on the floor of each cave and collected seeds every two weeks from March to May 2023. I found that the diet of oilbirds in this region of Colombia consists of 29 seed species: 14 were identified to species level, 4 to genus level and the rest remained as morphotypes. The colonies in the different caves showed differences in diets. Las Palmas cave, located at the highest altitude, showed the highest seed species richness, and Berlin cave, located at the lowest altitude, showed the highest number of certain seeds species compared to the other caves. This study provides information on the diet of the oilbird and its variation among colonies located at different altitudes.
