Timing of the evening emergence from day roosts of the grey-headed flying fox, Pteropus poliocephalus: the effects of predation risk, foraging needs, and social context

  • Justin A. Welbergen
Original article


This study addresses the functional question of how variation in foraging strategy, predation risk, and social context influence the timing of the evening emergence from day roosts of the grey-headed flying fox, Pteropus poliocephalus. The onset of evening emergence was expected to vary according to the relative costs and benefits of emerging early and should, therefore, reflect an optimal trade-off between predation risks and foraging needs. The onset of the colony-wide emergence was closely correlated with the time of sunset and cloud cover. However, as expected, the onset of the colony-wide emergence was delayed when a diurnal avian predator was present, whereas the onset was advanced during lactation when presumably energetic demands are higher. The trade-off between predation risks and foraging needs was further reflected in the emergence times of individual bats: adult females emerged earlier when they had higher foraging needs as indicated by their body condition; young emerged later when they were smaller and likely to be more at risk from predation due to their less developed flying skills. However, the emergence time of adult males depended on their social status: smaller bachelor males emerged from the colony earlier than larger harem-holding males who guard their harems until the last female had left. Thus, whereas the colony-wide emergence time reflected the outcome of a trade-off between predation risks and general foraging needs, on an individual level, the outcome of this trade-off depended on sex, age, body condition, and structural size and was modified by social context.


Bats Megachiroptera Emergence timing 



I am grateful to Nick Davies, Tim Clutton-Brock, Paul Racey, Jane Reid, Claire Spottiswoode, Jacob Fahr, and three anonymous referees for their constructive comments on the manuscript. I thank Suhel Quader and Patrick Fitze for their helpful comments and statistical advice. I thank Stefan Klose, David Kaiser, and Tane Sinclair for their help in the field. I thank Anne Goldizen for her academic support, Wendy Christie, Linda Weatley, Gwen Driebeek, Brad Rose, Jan Sinclair, and Justin Twohill for providing logistical support, and G. H. Williams for allowing me to work on the Dallis Park property. This work was supported in part by studentships to J. A. Welbergen from the National Environment Council (NER/S/A/2000/03282), King’s College Cambridge Internal Studentship, Isaac Newton Trust, and the Cambridge European Trust. The work was performed according to the Australian NSW Department of Agriculture guidelines for ethical treatment of animals and under license from the Australian Bird and Bat Banding Scheme and the Australian NSW National Parks and Wildlife Service.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Department of ZoologyUniversity of CambridgeCambridgeUK

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