Assertion : All birds, except the ones like koel (cuckoo) build nests for retiring and taking rest during night time (day time for nocutrnal) Reason : Koel lays its eggs in the nests of tailor bird.

Step-by-step solution

Koel and cuckoo need not build nests because they transfer their responsibilities to build nests, incubate eggs and nurture hatchlings to other birds specially crows. Thus they are called as "brood parasites". Being the brood parasite of the crow, the koel's breeding cycle synchronizes with that of crow. Both the koel's and crow's eggs are grey-green with rusty brown markings. Tailor bird is a garden bird which makes its nest by sewing, it has no direct relation with koel and cuckoo