Within-season dispersal does not protect re-nesting great reed warblers (Acrocephalus arundinaceus) from repeated common cuckoo (Cuculus canorus) parasitism

The co-evolutionary arms race between brood parasites and their hosts involves stepwise adaptive changes on the side of the parasites as well as hosts. In response to avian brood parasitism, host females may eject a parasitic egg, bury the parasitized clutch or desert it. After nest desertion, females commonly re-nest and may move further to avoid being parasitized again. Here we tested whether and under which conditions the within-season re-nesting prevents brood parasitism in the great reed warbler (Acrocephalus arundinaceus). We analysed 78 re-nesting events of 58 naturally parasitized host females that deserted their nests in response to the common cuckoo (Cuculus canorus) parasitism. The parasitism rate in the replacement nests of these females was 60%. Most of these females built their replacement nests less than 143 m from the previous nests. The probability for replacement nests to be parasitized increased with increasing instantaneous parasitism rate but not with the re-nesting distance or timing of the replacement clutch. We explain this by the high level of cuckoo parasitism across the whole study site during the major part of the breeding season. To better understand the patterns and consequences of host re-nesting behaviour, further studies in other host populations with different levels of cuckoo parasitism would be desirable.