To establish the genealogy of barn owls, we have to identify the parents of all clutches. During the daylight hours, when the mother broods the chicks, the ornithologists visit the nest boxes and capture the breeding females. When lucky, they also capture the breeding male that sometimes rests inside the nest boxes. Usually, the owls raise their chicks in pairs, faithfully. In most cases, the parents that feed the chicks are the biological parents, as cuckoldry is relatively rare.
If the captured owl is unknown to the ornithologists, we measure its size and shape. These data are useful to monitor the entire barn owl population over the years.
We also score plumage colouration: no two barn owls are similarly plumaged, and our research team tries to understand why that is the case. Every barn owl is photographed! During this nest visit, we also count and measure the eggs and nestlings. We obtain these precious data to follow the fate of every nest.