In many cuckoo species, at least, the cuckoo chick knocks the other eggs or hatchlings out of the nest. I'm not sure if that happens with this particular cuckoo species, but it seems likely. Fairy wren nests are absolutely tiny.
In any case, fairy wrens are very fast reproducers (raising 2-4 clutches per year), so I imagine they just start over with a new nest when this happens.
In any case, fairy wrens are very fast reproducers (raising 2-4 clutches per year), so I imagine they just start over with a new nest when this happens.