Common Terns on Oneida Lake

Jennifer Arnold, Stephen Oswald, Paul Curtis, Steve Grodsky (Funded by NYSDEC) 

Research, monitoring and management of Common Terns at Oneida Lake was continued in 2025. Oneida Lake supports a significant breeding population of Common Terns and has been closely monitored since 1979 in a collaboration between Cornell University and NYSDEC. Nic Fay (field tech) and Kyla Ebersole (field tech/researcher) both returned to work on the project as summer staff. Additionally, four Penn State undergraduates, along with other CBFS interns, participated in day trips to the tern breeding islands to contribute to waterbird research and management efforts. Gull exclusion grids and other management activities were very effective in preserving nesting areas for Common Terns at Little Island and Willard Island in 2025. Flooding in May from high water levels at Oneida Lake set breeding back a week and caused some early nest losses. During our peak count (9 June) there were 380 active Common Tern nests at Oneida Lake. 2025 was the most productive breeding season for Common Terns at Oneida Lake since 2017. Productivity (defined as number of chicks surviving to 18 days of age) was estimated as 0.72 chicks per nest (being three times higher in our fenced study plot at Little Island than at Willard Island). Breeding success at Willard Island was low because of considerable over-wash during storms leading to nest abandonment and loss of young chicks.

Oneida Lake is attractive to Common Terns and has strong potential to continue as an important tern colony in the region. However, long-term erosion (> 60% reduction in the size of Little Island since 2009) and over wash of tern breeding islands currently limit breeding habitat and productivity at Oneida Lake. Flooding causes direct egg loss, increases nesting densities on these islands, and leads to intraspecific aggression and death of young chicks, all of which reduce potential productivity. To persist at Oneida Lake, tern colonies need to more consistently achieve at least the level of productivity recorded in 2025 (which was the best breeding success in eight years). Island restoration for terns at Oneida Lake is vital to maintain numbers and increase productivity and help bolster declining regional populations.

Research this year saw the conclusion of tern diet studies using genetic metabarcoding (with Gemma Clucas, Cornell Lab of Ornithology) and research on soundscapes as a management tool at tern colonies (Kyla Ebersole). We also employed mark-recapture techniques to study population demography. These studies will help inform management of inland tern colonies to promote conservation of this state-listed species.