Male eclipse sunbird

Male eclipse birds are especially commonly found in Olive-backed Sunbirds.  The male eclipse plumage suggests that the bird is non-breeding.  In time, this plumage will graduate into adult breeding plumage, i.e. the iridescent blue-black in the throat and breast.

Meanwhile this bird will first develop a mere thin blue-black stripe down its throat and breast, as hinted here.

It's always interesting to see how the bird 'plays' with its food before swallowing it, so it's always 'now you see now you don't'.