Population trend of wintering terns at a stop-over site in Central Asian Flyway with special reference to the decline of Sandwich Tern

摘要

Because tern species are nomadic, changes in their populations can be mistaken for local colony shift or vice versa. As a result long-term observations on tern populations are needed in order to understand fluctuations in population trends. Given this need, we evaluated the population trends of wintering tern species at a stop-over site in the Central Asian Flyway, the Kadalundi-Vallikkunnu Community Reserve (KVCR), from 2005 to 2012 along the South-West coast of India. A total of ten tern species were identified, with some exhibiting fluctuations in their abundances. Sandwich Terns (Thalasseus sandvicensis), despite their status as a regular visitor in KVCR in 1989, declined sharply in abundance in the reserve, but increased in two adjacent locations, the Kannur and Manjeswaram beaches. These findings suggest that Sandwich Terns shifted their foraging ground from KVCR to adjacent habitats. Possible reasons for this shift include displacement of Sandwich Terns by the increasing abundance of Common Terns (Sterna hirundo) and Little Terns (S. saundersi), the lack of potential prey species availability, increased anthropogenic disturbance, and increased predator presence in the reserve.