Cuckoo

The bird in the photo is a Male cuckoo. 
A female bird is black in color.
Both of them remain together. Always.

The uniqueness of Cuckoos is that they don't build their own nest.
The female bird lays the eggs, generally in the nest of Crows.

Crows though smart, don't recognize the eggs of the cuckoo.
Crows incubate, hatch and nourish the chicks of her own and the stranger. 
Crows in that way are unbiased and treat all the chicks in the nest as of her.