Hosts have evolved a multiplicity of defensive responses against avian brood parasites. One of them is mobbing behaviour which often includes direct contact attacks. These aggressive strikes may not only distract the parasites but may also be fatal to them, as documented by cases of dead brood parasite females found near host nests. Here, we present the first video-recording of a great reed warbler (Acrocephalus arundinaceus) host whose vigorous nest defence appears to directly lead to the death of a female common cuckoo (Cuculus canorus). We suggest that the chance of parasite death probably rises with the presence of unfavourable factors, such as water below the nest. Our observation supports previous suggestions that hosts may pose a lethal danger to their parasites.
Parental care is advantageous because it typically increases the survival of genetically related young. In contrast, parental care given to unrelated young incurs no benefit. A further cost of parental investment is that it reduces the future reproductive potential of the caregiver. I examined whether eastern phoebes’ Sayornis phoebe future reproductive effort was related to interspecific brood parasitism by brown-headed cowbirds Molothrus ater in prior broods. In 2000 absolute and relative measures of change in clutch sizes from first to second breeding attempts were similar in parasitized and non-parasitized broods, while the latency to renest was several days shorter for parasitized broods. In addition, the relative change in clutch size was more negative for phoebe nests with more cowbird chicks per brood. In 2001 these statistical relationships between absolute and relative measures of residual effort and prior parasite load were also confirmed in control but not in experimentally manipulated clutches. The experimental data support previous findings that parasitism per se does not seem to influence residual reproductive output of adult phoebe hosts. These data also emphasize that intragenerational residual costs of parental care should be measured by the use of a relative measure of reproductive effort or other statistical methods that take into account the biological and statistical non-independence of clutch sizes from subsequent breeding attempts.