Population estimation is key to establishing population trends and assessing extinction risks of a species. In studies of colonial or nocturnal birds, traditional estimation methods present biases that make it difficult to trust and interpret the results, creating the need to generate new techniques to overcome these difficulties. The oilbird (Steatornis caripensis) is a strictly frugivorous nocturnal and colonial bird that roost in caves. In areas with continuous forests, colonies can be as large as 20,000 individuals. However, information on colonies inhabiting areas with fragmented forests is yet scarce. My goal was to estimate the size of oilbird colonies in nine caves in the department of Santander, Colombia, using a method a standardized a point-count method coupled with thermal cameras outside and inside the caves. My results indicate that colony size varied between 11 and 1524 individuals in the months of January and June, and showed no differences between breeding and non-breeding seasons. Also, between 0 and 34.7% of the total population of the colony remained in the cave after a strong peak of activity. My estimations based on thermal imaging are comparable with the traditional point count method and provide additional advantages such as data storage, and can be analyzed in other aspects, this supports the use of non-invasive technology in the study of wildlife.
