Alleviating competition increases raptor breeding success: A case study of Jackdaws and Lesser Kestrels

Anthropogenic changes in the natural environment have led to the need to find alternative resources to ensure the persistence of biodiversity. In birds, nest sites can be a limiting resource in stenotopic populations. A method of active protection is the building of nest boxes. However, attractive nest sites attract target species and their competitors. From the species conservation point of view, our target species was the Lesser Kestrel (Falco naumanni), whose populations have recovered owing to the establishment of nest box colonies across Europe. However, they have been out-competed by Jackdaws (Corvus monedula) in recent years. Because corvids are intelligent and aggressive, we had to artificially control the competition from Jackdaws to allow Lesser Kestrels to nest. We aimed to discourage Jackdaws from taking over the studied colony and to ensure the continued breeding of Lesser Kestrels by manipulating access to the nest boxes. Data were collected during three breeding seasons in a Lesser Kestrel nest box colony using two manipulations in which we prevented Jackdaw occupation by closing some of the nest boxes and then gradually opening them. We found a significantly lower probability of Lesser Kestrels nesting and lower breeding performance in the control year than in the years in which access to the boxes was manipulated. The field experiment shows the high efficiency of manipulating the accessibility of nest boxes by closing and opening them at the right time in the context of their occupation by the target species and thus influencing their breeding performance.