The cockop doesn't bother that the parent is hrre : the brooding parent even raises to give way to its own offspring or egg pushed away by the parasitic cockoo.

The parent bird is clueless and it happens all the time. Birdbrain, remember??

The cuckoo chick is clueless too. It is born with a sensitive And muscular back. When anything touches its back, it has a powerful instinct to push back til its not being touched anymore. As it gets feathered it no longer experiences this. The cuckoos bio mom puts in nest timing it to hatch 2 days before its foster siblings. This gives it chance to push out their eggs or failing that, to be fed 2 days no competition then be strong enough to toss out hatchlings. If it fails to do this, and mom is feeding sibs, it may be the one rejected because it no longer has the means to push them out.

Oh so that’s how it works. I was wondering how they knew to start pushing the other eggs or chicks out. Hm. Interesting. 🤔