Decadal banding efforts pay off: Assessing Chinese Crested Tern conservation through resighting data

The critically endangered Chinese Crested Tern (Thalasseus bernsteini, CCT) and its common flocking companion, the Greater Crested Tern (Thalasseus bergii, GCT), have been the focus of targeted recovery efforts in the Jiushan Archipelago of Zhejiang Province, China since 2013. To evaluate the long-term effectiveness of these measures and address key knowledge gaps in population dynamics and migration ecology, we analyzed ten years (2015–2024) of banding and citizen science data, comprising 116 CCT and 3501 GCT resighting records. We estimated survival rates using both directly derived survival rate (based on resighting rate after two years) and Cormack-Jolly-Seber modeling, and examined migration connectivity and climate risks. Results showed robust juvenile survival: modeled survival for the tern chick population was lower in the first two years (63.9 ± 12.0%) but exceeded 78% thereafter. This was also supported by resighting rate after two years: CCT 77.27%, GCT 70.42%. A key divergence in post-breeding migration was identified: CCT moves northward to stopover sites such as Nantong, Rizhao, and Jiaozhou Bay, whereas GCT migrates southward. Climate data confirmed that northern stopover sites do not pose higher storm risks, indicating that CCT’s northward migration is not a population liability. Furthermore, connectivity among breeding islands in Zhejiang and the Matsu Archipelago reveals a nascent coastal breeding network along China’s coast. These findings underscore the importance of protecting both the northern migration route and the breeding island network to ensure full life-cycle conservation of CCT.