<b>First report of dual cuckoo parasitism and egg recognition in the Chestnut-eared Bunting (Emberiza fucata)</b>

The arms race between avian brood parasites and their hosts represents a key selective pressure driving the evolution of egg phenotypes. Coevolutionary theory posits that the unique phenotypes (e.g., mimicry precision) evolved by both parties at the egg stage determining their fitness advantages. This study investigated cuckoo parasitism and egg recognition ability in the Chestnut-eared Bunting (Emberiza fucata) in the karst region of Liuzhi, Guizhou, southwest China. A total of 19 breeding nests were identified, of which 2 were parasitized by the Asian Emerald Cuckoo (Chrysococcyx maculatus) and Common Cuckoo (Cuculus canorus), respectively, with one deserted nest having 2 host eggs and 1 Asian Emerald Cuckoo egg in 2024 and another nest having 3 host eggs and 1 Common Cuckoo egg. Both cuckoo eggs have a phenotypic mismatch to the host eggs. Egg experiments involving non-mimetic white model eggs was conducted in 11 nests of Chestnut-eared Buntings and results showed that 100% of hosts rejected model eggs via beak-mediated egg removal within 3 days, indicating a robust ability to recognize non-mimetic eggs. This study is the first to document dual parasitism of the same Chestnut-eared Bunting population by two parasitic cuckoo species. We hypothesize that multiple cuckoo parasitism may be linked to limited available host species and to accidental parasitism driven by reproductive sympatry, which should be addressed in future research.