Factors Shaping Occurrence Probability of a Generalist Raptor Species across an Urban-Rural Gradient

Abstract

Urbanization constitutes one of the most intensive and fast spreading factors explaining biodiversity loss worldwide. The extension of urban areas and landscape configurations affects the ability of raptors to exploit urban patches. The Tawny Owl Strix aluco is a forest-dwelling nocturnal species with a wide distribution range that is well-adapted to urban environments. However, it remains unknown which habitat factors explain its presence in urban-associated landscapes. Our main objective is to determine the effect of urban landscapes on the probability of occurrence of Tawny Owls along an urban-rural gradient. It is expected that Tawny Owls will be able to use urban patches that have (1) at least 30% tree cover thanks to gardens/parks for hunting but (2) they will not use those with high noise levels (i.e., highways). Our research was carried out in the municipality of Donostia-San Sebastian in the Basque Country, Northern Spain. Data were obtained from a survey conducted in 2017. The municipality was divided into 329 square cells, of which 251 were surveyed. Tawny Owls were detected in 141 cells, and we found that nocturnal noise level and scrub cover contributed most to explaining the probability of Tawny Owl occurrence; with nocturnal noise having a significant negative effect on occurrence probability, and scrub cover a positive effect, probably because the species uses open or semi-open areas to hunt (but woodland to breed). Overall, it can be concluded that the very noisy and/or urbanized parts of the city comprised a non-optimal habitat for the species.-Pagaldai, N., Rodríguez-