The population trend of the largest breeding colony of the Indian Swiftlet Aerodramus unicolor: is it on the verge of extinction?

Abstract

Fluctuations in animal populations are indicators of environmental change. Populations of the Indian Swiftlet Aerodramus unicolor on the Burnt and Old Lighthouse islands of Vengurla rocks, Sindhudurg district, Maharashtra were assessed using the logistic growth model. The study used secondary literature and primary surveys to estimate breeding population sizes on both islands. To understand population dynamics, we calculated the carrying capacity (K) using the Verhulst population growth model, and the percent rate of change in populations. Swiftlet populations on both islands are considered to be the maximum size their habitat can sustain, not exceeding 5,000 and 246 birds on Burnt and Old Lighthouse islands, respectively. These populations were observed to fluctuate between 2020 and 2023, with change rates of 5.5% on Burnt Island, and -53% on Old Lighthouse Island. The logistic growth model indicates that these Indian Swiftlet populations are fluctuating near the carrying capacities of their habitats, which could gradually lead to extinction. This highlights the urgent need for conservation and regular monitoring of these populations in Vengurla rocks.