Geographical variation in breeding chronology of Germain’s swiftlet (Aerodramus inexpectatus germani) in southern Thailand

Abstract

The Germain’s swiftlet (Aerodramus inexpectatus germani) feeds on flying insects whose distribution and abundance are influenced by climatic conditions, especially rainfall. In turn, insect availability influences the onset of breeding by swiftlets, hence regions with different climatic conditions such as the west and the east coasts of peninsular Thailand should differ in swiftlet breeding chronology. Here we aimed to determine the variation in breeding chronology between the west and east coast colonies and relate this to insect availability. For each side of the peninsula, at least 40 breeding pairs were continuously observed (July 2014 to October 2015), using ‘internet protocol’ infrared cameras installed inside four commercial swiftlet houses. Flying insects were trapped every two weeks using sticky traps at three permanent stations within major foraging habitats. The onset of breeding in the western colonies was earlier than in the eastern colonies. These significant differences were explained by rainfall and food availability that showed synchrony between the nestling feeding period and peaks in insect biomass. Rainfall of 100–300mm month−1 overlapped with peak breeding and peak insect biomass. These findings have significant implications for the sustainability of swiftlet nest harvesting and demonstrate that, to minimise negative reproductive outcomes for swiftlets where nests are harvested, the timing of harvesting should consider regional climatic conditions.