The importance of nest cleaning in egg rejection behaviour of great reed warblersAcrocephalus arandinaceas

Abstract

We tested the importance of nest cleaning in egg rejection behaviour of the great reed warblerAcrocephalus arundinaceusin a highly parasitised population in which about 64% of nests are parasitised by the common cuckooCuculus canorus. Three types of objects of the same weight, texture and colour but with different shapes (dummy cuckoo eggs, sticks and disks) were placed into great reed warbler nests. We investigated the response of hosts in two stages of breeding: pre‐incubation when the risk of brood parasitism is high, and during incubation when the risk of parasitism is low. The dummy cuckoo eggs were rejected less often than the other objects in both breeding stages, although we did not find any difference in the frequency of rejection between pre‐incubation and incubation. We integrate these results into current views on the evolution of host–parasite interactions, and propose a hierarchical concept to understand egg rejection behaviour: (1) hosts reject all non‐egg shaped objects as a general cleaning mechanism; (2) adaptations for the hosts' ability to recognise their own eggs allows them to distinguish these eggs from similar objects and parasitic eggs.