Understanding urban foraging in a crepuscular insectivorous bird: Drivers of urban habitat use by the European nightjar (Caprimulgus europaeus)

Details

Supervisors

Evens, Ruben ; Creemers, Jitse

Faculty

Faculté des sciences

Degree label

Master [60] en sciences biologiques

Abstract

enThe rapid expansion of urban infrastructure has profoundly transformed nocturnal environments through Artificial Light At Night (ALAN), which includes both diffuse skyglow and localised light sources such as streetlights and illuminated infrastructures. While skyglow operates at broad spatial scales beyond urban boundaries, localised light sources generate sharp illumination gradients that can directly influence the behaviour of nocturnal organisms. In this study, we investigated urban foraging in the European nightjar (Caprimulgus europaeus), a crepuscular, vision-dependent aerial insectivore. Multi-year GPS tracking data (2015–2024) from a breeding population in Flanders (Belgium) were used to quantify the propension to use urban habitat across three dimensions: (i) occurrence and recurrence of urban foraging, (ii) individual foraging profiles, and (iii) spatial and temporal environmental conditions associated with these behaviours. Results show that 33% of individuals used urban areas at least once, although urban foraging represented a minor proportion of overall foraging activity. A strong individual component was detected: most birds avoided urban areas or used them only occasionally, while a smaller subset repeatedly exploited urban hotspots. Spatially, artificial radiance increased the probability of entering urban environments, but repeated use was more frequent in moderately urbanised and structurally open landscapes than in densely built areas, highlighting an interaction between artificial light and landscape structure. At finer scales, hotspots varied with local lighting configurations and types of artificial light sources, suggesting that specific lighting characteristics may influence site use. Temporal patterns further indicated that nocturnal conditions modulate urban foraging: dusk was associated with extensive movements, hotspot use peaked early in the night, moonlight facilitated urban entry, whereas cloud cover increased hotspot use, likely through enhanced skyglow. Overall, this study demonstrates that urban foraging in the European nightjar is a context-dependent and highly individualised strategy shaped by the interaction between individual behaviour, landscape structure, and nocturnal illumination. Urban areas therefore act as supplementary foraging environments rather than core habitats, used sporadically by most individuals and more consistently by a subset. These findings also highlight that urban use extends beyond strictly urban land-cover classes into peri-urban mosaics, emphasizing the need to consider the functional nocturnal landscape rather than relying solely on administrative land-cover classifications.