ABSTRACT Brood parasitism by the Common Cuckoo ( Cuculus canorus ) depends on precise timing, with females typically laying during the host's laying phase to ensure their chick hatches first. While cuckoos are known to remove one or two host eggs during laying, complete destruction of host clutches at this stage has been rarely documented. Here, we present five video‐documented cases of cuckoo clutch destruction during laying in Vinous‐throated Parrotbills ( Sinosuthora webbiana ), a semi‐colonial host that breeds synchronously. Across visits lasting only 2–72 s, cuckoos swallowed, broke, or carried away host eggs, resulting in the loss of 1–4 eggs per event and eventual desertion of all nests. Such behavior at the very stage most favorable for parasitism appears paradoxical, yet may serve conditional functions: resetting host reproduction when cuckoos are not ready to lay, or eliminating nests deemed unsuitable under synchronous breeding conditions where many options are available simultaneously. A further consequence is that hosts lose opportunities to reinforce egg‐recognition templates, potentially weakening defenses in subsequent attempts. These findings highlight the importance of early‐stage interactions in the host–parasite arms race and suggest that laying‐stage clutch destruction represents a previously overlooked element of cuckoo reproductive behavior.
Lee et al. (Wed,) studied this question.