Mention the changes the koel must have undergone in order to achieve brood parisitism , during the course of evolution

Dear student 

Brood parasitism is a phenomenon in which one organism lays its egg in the nest of another.

During the course of evolution the koel's egg have evolved to resemble the egg of  host's bird i.e crow in  both size and colour in order to reduce the chances of host's bird detecting the koel's egg  and ejecting them out of the nest.

Regards