Commuting to forage: spatiotemporal variations in commuting flights of a crepuscular insectivorous bird, the European Nightjar (Caprimulgus europaeus)

Details

Supervisors

Evens, Ruben

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

enCentral-place foraging, a strategy that depends on fine-scale variaEons in environmental condiEons to modulate its occurrence, duraEon and distance, remains poorly understood. This is parEcularly true for crepuscular animals, mainly due to their discreet nature. The European Nightjar (Caprimulgus europaeus), a visually hunEng insecEvore, provides an ideal model to invesEgate how movement behaviour between breeding territories and foraging sites is shaped. Using GPS loggers deployed on a populaEon of Nightjars in Flanders (Belgium) over ten consecuEve breeding seasons, we quanEfied the occurrence, distance, and duraEon of commuEng flights outside breeding territories. We then tested how these components varied with sex, habitat configuraEon through study area, breeding stage (presence of chicks), and the light environment, a key determinant of foraging efficiency in this species. The probability of commuEng flights was primarily driven by the Eme of night, with peaks at dusk and dawn, when light condiEons are opEmal for visual hunEng. In contrast, the distance travelled to foraging sites was influenced solely by area, reflecEng spaEal variaEon in the proximity of suitable feeding areas to breeding territories. Trip duraEon was modulated by both light condiEons and breeding stage. The absence of a moon above the horizon or clouds resulted in shorter foraging trips, likely reflecEng insufficient light for effecEve prey capture. Similarly, females undertook shorter trips when chicks were present, indicaEng increased nest aCendance and sex-specific parental investment. Before chick rearing, females showed a higher likelihood of leaving the territory and tended to remain away for longer than males, a paCern consistent with male-biased territory defence. Overall, our results demonstrate that Nightjar commuEng behaviour is finely tuned to a combinaEon of environmental and reproducEve constraints, parEcularly study area, the presence of chicks, and the nocturnal light condiEons driven by solar elevaEon, the presence a moon above the horizon, and cloud cover. These results therefore allow a beCer understanding of crepuscular aerial insecEvores, enabling more informed decisions to be made to protect these groups of birds.