This species is also known as the Pacific Reef Egret (OBC, Robson) but here I follow Clements who calls it Pacific Reef-Heron (IOC goes with Reef Heron without the hyphen). These birds occur in both a dark morph as seen here, and also a white morph which bears a resemblance to the Chinese Egret (Egretta eulophotes). On our visit we only saw dark morph birds fishing from a concrete seawall. They foraged like a kingfisher, flying out over the water, grabbing fish from the water's surface with their bill and returning to the wall. Such aerial feeding was noted by Hancock & Kushlan (1984) and Marchant & Higgins mention that they may "hover while stabbing at water from air." Two races are recognized. This is the widespread nominate race. Another larger race with a darker bill (E. s. albolineata) is confined to New Caledonia and Loyalty Islands. Digiscoped with Panasonic Lumix LX5 | Nikon Fieldscope III | 30X hand-held, no adapter.
References:
Hancock, J. & J.Kushlan. 1984. The Herons Handbook. Harper & Row, New York.
Marchant, S.; Higgins, P.J. (eds.) 1990. Handbook of Australian, New Zealand and Antarctic birds. Vol. 1, ratites to ducks. Oxford University Press, Melbourne.
Martínez-Vilalta, A., Motis, A. & Kirwan, G.M. (2019). Pacific Reef-egret (Egretta sacra). 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/52696 on 25 March 2019).