Is the Black-Browed Reed Warbler (Acrocephalus bistrigiceps) a Suitable Host for the Common Cuckoo (Cuculus canorus)?

Avian brood parasitism constitutes a classical model for studying coevolution. The discovery and reporting of cuckoo parasitism on various new hosts contribute to a deeper comprehension of the coevolutionary relationships between these parasites and their hosts. This study involved field monitoring of the black-browed reed warbler (Acrocephalus bistrigiceps, BRW) in a reed wetland of northeast China during the breeding seasons for 13 consecutive years (2012–2024). A total of 677 BRW nests were monitored, and only three cases of cuckoo parasitism were detected, for a parasitism rate of 0.44%. An egg recognition experiment indicated that the BRW possesses a relatively strong egg recognition ability and can effectively reject foreign parasitic eggs. The color characteristics of common cuckoo and BRW eggs are considerably different. Through the analysis and comparison of egg color spectra between cuckoo and warbler eggs, combined with the field cuckoo parasitism rate and egg recognition ability of warblers, we concluded that the BRW is not a commonly used host for the common cuckoo.