The ornithologists equip barn owl parents with GPS in order to follow very precisely where they hunt, where they rest at night and roost during the day. The adults are captured when the offspring are one month of age. To do so, an automatic trap is installed at the nest box. The ornithologists are experienced and work very quickly to avoid disturbing barn owls too much. The GPS is a small box weighing 12 grams fixed on the back of the birds with a harness.
We fix a camera trap in front of each nest box to take pictures automatically when there is movement close to the nest-box entrance. We thus get pictures when the parents enter and leave their nest box. On the pictures, we can identify prey species, and when coupled with the data obtained from GPS, we can determine where different prey species are captured (e.g., in agricultural fields, along forest edges, in villages).
After 10 days, the ornithologists re-capture the owls equipped with a GPS to remove it and download the data (every 10 seconds we have the coordinates of the location where the owls are). We also collect the pellets that are ejected orally by the barn owl nestlings to compare the diet identified with the camera traps and what the owls actually consume.