Roosting patterns of the Edible-Nest Swiftlet (Aerodramus fuciphagus) of the Andaman Islands: effects of lunar phase and breeding chronology

Environmental conditions and biological rhythms can affect the behavioural routines of animals. However, the effect of lunar phase on individual roosting behaviour remains uninvestigated in most species. Here, we monitored the effect of lunar phase, sunset time, temperature, humidity and the breeding chronology on the roosting patterns of the Edible-Nest Swiftlet (Aerodramus fuciphagus) of the Andaman Islands, across breeding stages. Counts revealed that more than 98% of the population returned to the roosting caves during peak roosting hours, i.e. 1700–2000h. The proportion of birds roosting in caves was highest during the ‘new moon’ phase and when birds were at the nest-building and fledging stage of their breeding cycle. We confirmed that the variation in the roosting behaviour of the Edible-Nest Swiftlet is linked both to the stages in the breeding cycle and to the lunar phase. We hypothesise that the cause for the lunarphilic roosting pattern is an anti-predator strategy. Feeding habits and food requirements during different breeding stages are presumed to influence the roosting pattern of the species. An improved understanding of the association of the behaviour, physiology and the environmental conditions which influence these traits can only help us improve conservation outcomes for this economically important species.