Dieta y reproducción en una colonia de guácharos (Steatornis caripensis) de alta montaña en Colombia

I studied the diet and nestling development in a colony of Oilbirds (Steatornis caripensis) at an elevationof 2900 m in the Eastern Andes of Colombia between April and December 2011. The fruits consumed bythe oilbirds were identified and analyzed to establish the nutritional content of the pulp of each species.Colony members consumed the fruits of 16 plant species: ten of the family Arecaeae, five of Lauraceaeand one of Myrtaceae. The families of plants most consumed by oilbirds match those reported in differentstudies in Venezuela, Ecuador and Trinidad and Tobago. The species with the highest numbers of seedscollected during the study were the palms Oenocarpus bataua, Ceroxylon quindiuense and Geonomaweberbaueri. The species of Lauraceae showed a well-defined fruiting period in the first half of the year,while the palms were less seasonal, their seeds being found in all samples. The beginning of the oilbirds’breeding season coincided with the rainy season (April to June) and the increased availability of fruits ofLauraceae, which on average had a high lipid content, a low protein content and a moderate carbohydratecontent. The palms had higher carbohydrate content, and slightly higher protein content but lower lipidcontent. Adults of the colony had to fly to lower elevations over distances of up to 150 km to obtain somefruits. Nestlings in this colony took ca. 185 days to reach fledging, 30% longer than those in lower-elevation colonies, probably due to the necessity of devoting much energy to thermoregulation. Thepersistence of this colony at such an extreme elevation probably reflects characteristics of the caveenvironment and the high mobility of the adults to obtain nutrient-rich fruits.