The sunbirds are a group of very small birds which feed largely on nectar, although they will also take insects, especially when feeding their young. Their flight is fast and direct on their short wings.
This bird is also known as Yellow-bellied Sunbird, and its scientific name is Cinnyris jugularis (formerly Nectarinia jugularis). The Olive-backed Sunbirds in this blog were spotted at Sengkang Riverside.