Black tern nest-site fidelity in unstable habitat: preliminary study

We investigated the adult Black Tern (Chlidonias niger) return rate and nest-site fidelity in unstable habitats in the Kaniv reservoir (Middle Dnieper, Ukraine) where a regular weather impact such as heavy rains and storms leads to a destruction of nesting colonies. 278 adult birds were tagged with colored rings in 12 Black Tern colonies during the nesting season in 2012-2019. 44 Black Tern birds were resighted or recaptured in eight colonies. The return rate was 15.8 % and it declined rapidly in 3 years. 29 returning terns were noted within the same colonies where the birds had been tagged initially, 15 ones were seen in other colonies, but the majority of them were found no farther than 2 km from the initial colony. The site fidelity mean rate was 66 %. Olgin colony showed a high nest-site fidelity rate, while it was much lower in others. Such variations occurred because of the loss of first clutches caused by unfavorable weather conditions. In the middle of May, strong waves, storms and heavy rains regularly destroyed nesting colonies located in habitats poorly protected by water plant vegetation. Terns relocated their colonies to build new nesting clutches but commonly not farther then 2 km from their first colonies.