Prey composition in the diet of an avian aerial insectivore – the Barn Swallow ( Hirundo rustica ) in the Indian Himalaya

Aerial insectivores are experiencing rapid population declines worldwide, with the Barn Swallow (Hirundo rustica), a long-distance migratory species, declining at an alarming rate across its wide breeding range. Despite extensive study elsewhere, data on Barn Swallow ecology remain scarce in India, especially in the Himalaya, which constitutes the southern extent of its breeding range in South Asia. This study documents the diet of Barn Swallow nestlings across rural and urban settlements in the Uttarakhand Himalaya. In 2023, faecal samples of nestlings from four breeding sites (two rural and two urban) were collected to examine dietary composition, and simultaneously, aerial insects were sampled at one rural and one urban site to document prey availability. A total of 240 faecal samples were collected and analyzed, wherein six invertebrate orders were identified – Coleoptera, Hymenoptera, Hemiptera, Diptera, Isoptera, and Odonata, in decreasing order of their occurrence. The prey composition between rural and urban settlements differed significantly (R² = 0.17, F = 49.18, p = 0.001). There was no significant temporal variation in prey composition over the course of the breeding season (R² = 0.0084, F = 1.981, p = 0.118), except for changes due to seasonal and regional emergence of certain insect groups such as Isoptera. Insects sampled across urban and rural settlements revealed the presence of Diptera, Coleoptera, Hymenoptera, Hemiptera, Aranea, Orthoptera, and Lepidoptera. The community composition between available insect prey and dietary contents of Barn Swallow nestlings showed a significant difference (R² = 0.225, F = 86.39, p = 0.001). This study serves as a baseline for future research on the diet and insect prey availability of aerial insectivores in the Himalayan region. Understanding the impact of anthropogenic activities, such as pesticide use, abandonment of farmland, and urban expansion, prevalent in the Himalayan region on aerial insectivores would be critical. It is imperative to conduct long-term studies on insect availability and abundance, and on their influence on the nesting success of aerial insectivores such as Barn Swallows.