Use of digital trail cameras to study Bonelli's eagle diet during the nestling period

The study of avian diet is one of the most commonly discussed topics in Ornithology. Different methods such as direct observations of hunting, analysis of pellets and collection of prey remains have usually been employed to study avian diet. Fortunately, digital technologies have rapidly advanced in recent years, allowing researchers to increase our understanding of avian behaviour. Here we report the outcomes of a pilot project to study the diet of Bonelli's eagle (Aquila fasciata, Syn = Hieraaetus fasciatus) during the nestling period using digital trail cameras. We describe the monitoring system, provide results on dietary composition and discuss advantages and shortcomings of the method employed. Our results show that the main prey delivered to nests were pigeons (Columba spp.) and common rabbits (Oryctolagus cuniculus). One advantage of the method is the relative low cost of the material employed in contrast to digital video cameras. Disadvantages were the limited duration of power supply of the units and, because recordings can only be obtained at the end of the breeding season, it is not possible to fix the device if a problem arises. Nevertheless, in the light of our results, we recommend the use of digital trail cameras as an efficient, non-intrusive method to study the diet of cliff-nesting raptors, given that, in combination with traditional methods, it facilitates estimation of dietary composition in an objective, economic, contrastable and unbiased manner.