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.
The goal of this paper was to test the hypothesis that weather conditions, such as temperature and rainfall, affect egg colouration in the great reed warbler Acrocephalus arundinaceus. We failed to find strong support for this hypothesis; nevertheless, our results indicate that temperature has an effect on some egg colour characteristics. Eggshell brightness (PC1) increased with increasing temperature at laying and eggs were darker in the colder year of the two-year study. On the other hand, UV-blue colouration (PC2) scores were higher in the warmer year. The amount of rainfall, however, had no effect on eggshell colouration. As there is an indication from other studies that weather may have an effect on egg appearance through the food availability, we encourage further testing the environmental hypothesis in other bird species. If this holds for more bird species, this would have important implications for the hypotheses about the adaptive function of bright eggshell colouration.