Called Yellow-bellied Sunbird and placed in the large genus Nectarinia by Australian checklists (e.g. HANZAB). However Howard & Moore, IOC and Clements now place this bird in the genus Cinnyris with the English name Olive-backed Sunbird. The subspecies found on the Solomon Islands is C. j. flavigastra, sometimes spelled flavigaster. It is similar to C. j. frenatus found in New Guinea and Australia but has deeper yellow underparts. This is a male. The female is similar but lacks the striking iridescent blue gorget.
Sunbirds (Nectariniidae) are an Old World family of brightly colored nectarivores. Their colors are light-dependent, iridescent and ephemeral. These birds can be very active and occasionally hover in mid-air like a hummingbird. They lower their metabolism and body temperature at night during sleep to conserve energy; a strategy also used by hummingbirds. The long curved bill is used to extract nectar from flowers. Canon PowerShot SX60.
References:
Cheke, R., Mann, C., Christie, D.A. & Kirwan, G.M. (2019). Olive-backed Sunbird (Cinnyris jugularis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/60062 on 17 November 2019).
Dutson, G. (2011) Birds of Melanesia, Christopher Helm, London.
Gregory, P. (2017) Birds of New Guinea, Including Bismarck Archipelago and Boughainville. Lynx Edicions, Barcelona.