Timing pattern of Common Cuckoo parasitism and its relation to host nest attendance

Abstract

Classical works show the adaptive importance of precise timing of egg‐laying in brood parasitic Common Cuckoos Cuculus canorus to ensure sufficient incubation time and successful hatching. Laying in the late afternoon has been suggested to increase the chance of secretive parasitism and therefore escape the aggressive mobbing by hosts, yet this hypothesis has not been examined in more detail. We therefore used continuous video recordings of Great Reed Warbler Acrocephalus arundinaceus nests to explore (1) the overall timing patterns of cuckoo parasitism and host nest attendance, (2) how variation in nest attendance, both throughout the time of day and stage of the host laying period, relates to the timing of parasitism, (3) whether parasitism timing influences the likelihood that a cuckoo is detected by the host and (4) whether the timing of parasitism is repeatable among individual cuckoo females. We found that parasitism predominantly occurs during the initial days of the host laying period, with most events occurring after 14:00 h (2:00 PM). We also found that hosts are more present at their nests during the mornings and less so in the late afternoon, particularly at the start of their laying period. Our findings show that the timing of cuckoo parasitism is negatively associated with host nest attendance, but only early in the laying period. The cuckoo's preference for afternoon laying remains relatively constant throughout the laying period, even though it appears most beneficial at the beginning as the likelihood of host–cuckoo encounters increases later in the laying period and towards the evening. Nevertheless, the increasing nest attendance of Great Reed Warblers and the higher probability of encountering a cuckoo at the nest are probably not sufficient to disrupt the cuckoo's successful afternoon parasitic timing in the later stages, even though we observed a decline in the number of parasitism events over the laying cycle. Finally, a genetic analysis revealed that individual cuckoo females exhibit moderate repeatability in timing of parasitism throughout the day and none throughout the host laying cycle. We discuss the relationship between parasitism timing and host nest attendance, and potential implications of the observed patterns.