Conserving a urban habitat: Enhanced detection of common swift nests in buildings using a video fusion method.

Common swifts (Apus apus) nest in cavities and cracks in building facades and roofs. It is a declining species in Europe, partly due to the loss of suitable breeding habitat caused by urban building renovation (e.g. thermal insulation). In several countries, renovation projects must quantify the amount of habitat occupied by swifts that will be destructed, and provide compensatory measures, such as installing nest boxes in the renovated building. However, nesting swifts are uneasy to detect visually. We report a video method we used to improve swift nest detection. It is based on continuous filming of a building's facade (for 1-2 hours), and later video-frame fusion to reveal swift flying in and out of cavities in the facade. Based on a continuous dataset of swift passages during a full breeding season, we discuss favorable period in the season and day hours to efficiently detect nesting activity and assess building occupancy. We provide a software for other conservation projects that can use the same video-fusion method.