Spatial Vigilance Architecture of Indian Flying Fox Colonies in Rural Parts of Barak Valley, Northeast India

Pteropodids like the Indian flying fox roost gregariously and externally in tree canopies. In such conditions, hierarchy and competition for preferred roosting positions may result in the social structuring of animal aggregation. Vigilance is a manifestation of competition in canopy roosting bats, which can vary temporally, and according to the spatial position. The current study investigated the function of vigilance in terms of environmental vigilance (anti-predatory) and social vigilance. We expect the extent of vigilance to be influenced by the relative spatial position of the bat. Furthermore, we expect neighboring roost tree density to affect vigilance too. Pteropus giganteus showed varying levels of vigilance according to roosting architecture. Across all positions, on average, they spent 7% of their roosting time being vigilant. Peripheral bats on a roosting tree showed a significant increase in environmental vigilance compared to the core, thus confirming the edge effect hypothesis. Bats, however, displayed no significant variation concerning social vigilance as roosting positions were observed in the periphery and core. Also, neighbor roost tree density did not impact vigilance. Overall, we see that a spatial vigilance architecture prevails in a roosting tree. Plus, the very persistence of vigilance while day roosting/resting in huge numbers indicates a potential fitness advantage. Significance statement As bats spend over half their lives roosting, it is assumed that selective pressures of their roosting environment may have played a crucial role in their evolution, behavior, and ecology. Generally, the bats’ primary objective at roosts is resting, followed by social behavior and other maintenance activities. The major gap in terms of Indian flying foxes lies in their roosting architecture and environmental relations. In this study, we find an architectural design in the way bats roost and display their vigilance. The study points out that the main essence of vigilance theory is prevalent in Indian flying foxes. Total vigilance increased from core to periphery, which may reflect the existence of a risk gradient. Flying fox colonies have complex social organization and are highly structured.