This is an adult. Juveniles are similar but lack red patches. These colorful pigeons are endemic to the Solomon Islands and New Caledonia where it is uncommon and apparently only a seasonal visitor to Grande Terre. Formerly called Grey's Fruit-Dove. Canon PowerShot SX60.
References:
Baptista, L.F., Trail, P.W., Horblit, H.M., Boesman, P. & Garcia, E.F.J. (2019). Red-bellied Fruit-dove (Ptilinopus greyi). 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/54338 on 9 December 2019).
BirdLife International 2016. Ptilinopus greyi. The IUCN Red List of Threatened Species 2016: e.T22691440A93312723. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22691440A93312723.en. Downloaded on 09 December 2019.
Dutson, G. (2011) Birds of Melanesia, Christopher Helm, London.
Gibbs D, Barnes E, Cox J (2010) Pigeons and Doves: A Guide to the Pigeons and Doves of the World. Christopher Helm, London.