To minimise the costs of raising altricial offspring some species leave the nurture of their young to host species, which is known as brood parasitism. Interactions between these brood parasites and their hosts are a typical example for a reciprocal co-evolutionary arms race. A shared evolutionary history induced species-specific defence strategies to reduce the impact of parasitism Within this context this study compares early parasite detection behaviours by means of call recognition as well

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... s behavioural plasticity through the breeding cycle in an experimental design. For this purpose, host response was determined for a species naive to brood parasitism, the cave breeding blue tit (Cyanistes caeruleus), to investigate if a co-evolutionary context is necessary for this species to be sensible towards cuckoo calls or if risk related call learning occurs. The results suggest that blue tits are indeed able to learn adequate responses quickly as their behavioural patterns change significantly towards cuckoo calls. Also, this study compared the response behaviour of a regular cuckoo host, the red-backed shrike (Lanius collurio) and its behavioural defences according to their breeding stage and the parasites distance from the nest. The results revealed changes in defence strategy towards a cuckoo dummy within the breeding stage (e.g. incubation, nestling stage or fledgling stage). The birds behaved most cryptic during incubation. Alarm calls and attacks were performed most obviously during the nestling stage, which fits the nesting-cue or offspring-value hypothesises.