The use of artificial floating nest platforms as conservation measure for the common tern Sterna hirundo: a case study in the RAMSAR site Druzno Lake in Northern Poland

Abstract

Artificial nesting sites with floating platforms may effectively support local breeding populations of waterbirds (enhancing productivity and survival) when natural sites are unavailable. In this study, we installed three artificial floating nest platforms (one in 2017, two in 2020) and we evaluated their use as a conservation measure for the common tern Sterna hirundo breeding at a RAMSAR site in Northern Poland with limited natural nesting habitat. We analyzed local population dynamics based on direct census in the study area from 2013 to 2021 and using data from literature dating back to 1925, with emphasis on the effects of three artificial nest platforms. We found that the local common tern population exhibited steep decline during the period 1999–2021 (−92%). Birds accepted artificial nesting platforms in the first year of their installation. The number of pairs breeding in artificial nests in 2017–2021 made up 53–100% of the breeding population in the study area. The nest density, clutch size and mean breeding output were similar in all platforms during all seasons. In 2020, the water level in the lake rapidly increased (ca 50 cm in 24 h) and completely destroyed common tern nests in the natural islets, while the floating platforms were the only places in the nature reserve where common terns were able to nest and breed successfully. We conclude that artificial breeding platforms may be a good conservation measure for common terns in natural areas with limited access to breeding habitat (but with optimal foraging areas). Based on our experiences from the present case study and on experience of other authors we propose recommendations for constructing, placing, and maintenance of nest platforms for common terns.