Population trends of passage and wintering barn swallows (Hirundo Rustica) in Peninsular Malaysia

Abstract

In Peninsular Malaysia, passage and wintering Barn Swallows (Hirundo rustica) often congregate at nocturnal roosts in towns. As a Holarctic migratory species, it is at risk of population collapse. Despite extensive research, little is known about this species in its wintering grounds, especially in the tropics. This study aimed to determine how climate change influences the population growth of this species across a geographical area over a decade, from 2009 to 2019. A species distribution model was constructed using data obtained from the eBird database – a citizen science project – of records from diverse locations. We used the Kernel Density tool in ArcGIS to describe Barn Swallow density and expansion pattern across Peninsular Malaysia. We demonstrate that the Barn Swallow’s population has fallen by about 27.1% over the last decade. In 2009, the species was dispersed in two distinct areas: Perlis to Pulau Pinang; and the Pahang region bordering Selangor and Negeri Sembilan; in addition, some individuals chose to winter in south-eastern Johor. Within ten years, the flock has descended from Perlis to the northwest corner of Perak, while the vast wintering area in Pahang has decreased and stretched down to Melaka and Johor. The differences in Barn Swallow numbers and distribution patterns observed in this study could be a result of climate and land use changes which have caused this species to spread to parts of other wintering regions, altering the arrival and departure times of migration, thereby interfering with its breeding season.