Nocturnal Behavior of Wintering Common Cranes (Grus grus) Under Varying Environmental Conditions

Nocturnal conditions impose strong constraints on diurnal species, requiring behavioral adjustments to balance predation risk and social interactions. We investigated how environmental factors shape nocturnal behavior in wintering Common cranes [Grus grus (Linnaeus, 1758)] in central Italy during the 2022-2023 season, using an integrated approach combining camera trapping and acoustic monitoring. We quantified activity, vigilance, display, and vocal behavior in relation to night phase, moon illumination, cloud cover, and seasonal progression. Cranes exhibited high nocturnal activity overall (89.4% ± 2.1% of individuals per night), with 44.8% ± 3.9% showing vigilance. Activity peaked toward morning but decreased significantly with increasing moon illumination, and this effect was partially buffered by cloud cover. Vigilance followed a similar pattern, declining under bright conditions and increasing during darker periods, consistent with antipredatory responses. In contrast, display behavior was positively associated with moon illumination and increased over winter, indicating that cranes exploit illuminated conditions for visually mediated social signaling, possibly in preparation for migration. Vocal activity showed the opposite trend, being higher in darker conditions, indicating its role in maintaining social contact when visual communication is limited. Overall, Common cranes exhibit pronounced nocturnal behavioral flexibility, modulating different behavioral components in response to environmental cues. These findings show how external stimuli can act as selective forces shaping nocturnal strategies in diurnal species.