Barn Swallows Hirundo rustica in Peninsular Malaysia: Urban winter roost counts after 50 years, and dietary segregation from house-farmed swiftlets Aerodramus sp.

• Main Authors: Mansor, Mohammad Saiful, Halim, Muhammad Rasul Abdullah, Abdullah, Nurul Ashikin, Ramli, Rosli, Cranbrook, Earl Of
• Format: Article
• Published: National University of Singapore 2020
• Subjects: Q Science (General); QH301 Biology
• Online Access: http://eprints.um.edu.my/37105/

In Peninsular Malaysia, passage and wintering Barn Swallows often congregate at nocturnal roosts in towns, most conspicuously on utility wires and adjoining roofs and ledges. As a Holarctic migrant, the species is potentially susceptible to population crashes. The first objective of this study was to investigate half-centennial changes in the number of passage and wintering Barn Swallows utilising an urban most at Bentong, Peninsular Malaysia, through monthly counts following equal procedures in 1966-68. The second objective was to assess evidence for competition in terms of dietary overlap with a recently established population of house-fanned swiftlets (Aerodramus sp.) using both morphological identifications and next-generation sequencing (NGS). Modern peak numbers in October 2015, at 63,290 swallows, were 72% of the November peak of 1967 (87,880). The negative trend may reflect a declining swallow population in the Palaearctic breeding area but may also be a consequence of diminished resources in this tropical wintering region. A notable change during the half-century interval has been the introduction of a large population of trophically similar house-farmed swiftlets Aerodramus sp. exceeding passage and wintering Barn Swallows at peak numbers. At an ordinal level, the diets of Barn Swallows and house-fanned swiftlets both include a high proportion of hymenopterans, but at the level of genus, there is dietary separation between them. Molecular NGS data based on lower taxonomic levels (i.e., family, genus, and species) showed only about 10% overlap. We conclude that, after an interval of half a century, dietary competition with the new resident population of house-farmed swiftlets is unlikely to account for the reduction in peak numbers of migratory Barn Swallows.