The Beautiful Sunbird (Cinnyris pulchella) (formerly placed in the genus Nectarinia), is a sunbird. The sunbirds are a group of very small Old World passerine birds which feed largely on nectar, although they will also take insects, especially when feeding young. Flight is fast and direct on their short wings. Most species can take nectar by hovering like a hummingbird, but usually perch to feed most of the time.
The name and the description are the same. I managed to get a few good photos in Ndutu and Tarangire.
The much duller female
They have a large range stretching from the West Coast of Africa to Ethiopia in the east and as far south as Tanzania. Look for them in flowering plants in lodges, they seem to know a good free feed when they see one! The red dot shows Ndutu where I had my best sighting.
There are a few clips from the Gambia on IBC as well as this one from YouTube.