Host Exploitation by Cuckoos in China: A Review and Real-Time Tracking Program for Parasitism Records.

China stands as a global hotspot for cuckoo diversity and their avian hosts, presenting an unparalleled natural laboratory for investigating brood parasitism and co-evolutionary dynamics in avian systems. Through an extensive synthesis of published literature, verified media reports, and meticulously curated visual documentation contributed by citizen scientists, we present a comprehensive update on cuckoo-host diversity and their intricate ecological relationships across China. Our study identifies 17 cuckoo species, with 15 confirmed as brood parasites exploiting an extensive network of 142 host species spanning 74 genera and 34 families within the passerine assemblage. While we observed broad overlaps in the ranges of host body mass and egg volume across different cuckoo species, phylogenetic generalized linear mixed models reveal significant patterns of adaptive matching in both body mass and egg volume parameters between cuckoos and their respective hosts. Our findings demonstrate striking specificity in host selection, with minimal overlap in actual host species utilization among sympatric cuckoos, suggesting sophisticated niche partitioning strategies to mitigate interspecific competition. Nevertheless, critical knowledge gaps persist, particularly regarding the evolutionary dynamics of egg phenotype mimicry in relation to specific host species. Finally, we introduce a real-time tracking program designed to engage citizen scientists in ongoing documentation of parasitism events, facilitating dynamic updates to host-parasite records.