Moult and plumage patterns of the critically endangered Yellow-breasted Bunting ( Emberiza aureola ) at a stopover site in Korea

Travelling from across its breeding range in northern Eurasia, Yellow-breasted Buntings ( Emberiza aureola ) stopover in China before migrating to their wintering areas in South-East Asia and the Indian subcontinent. This species is now considered critically endangered because its global population has declined dramatically; moreover, it is overexploited by illegal trapping at its stopover sites during the moult. Currently, two subspecies of the Yellow-breasted Bunting are recognized: aureola and ornata . However, the moult strategies of these subspecies at their stopover sites remain unknown. In the present study, we analysed the moult and plumage patterns of E. a. ornata in Korea ( n = 262) between 2005 and 2018 as part of a long-term bird ringing project at a key migrant stopover site. We observed significant sexual dimorphism in the morphological characteristics of both adults and immatures: the males had longer wings, tails, and tarsi, and weighed more than the females. Moult patterns were distinct in relation to age. Adults underwent a complete post-breeding moult, entirely replacing their body and flight feathers before the onset of autumn migration over a breeding range. Remarkably, 93.4% of first-winter birds underwent an eccentric primary moult, having moulted the 3–4 outermost primaries (P6–P9 or P7–P9) before arriving at the stopover site. Males achieve full adult breeding plumage in their second summer. More than three types of median wing coverts were identified in the first-winter males, with various plumage colours and patterns. To the best of our knowledge, this is the first report on the moulting and plumage patterns in the subspecies ornata as it passes through an East Asian migratory flyway stopover site in Korea. Our results will contribute to an understanding of the migration behaviour and subspecies populations that are at risk in their specific environments. This is essential for ecological monitoring to facilitate the conservation of this critically endangered species.