Canon PowerShot SX60 HS.
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)
This species was deliberately released in Hawaii staring in 1959 and they are now well established on all the main islands. These are the smaller nominate race, sometimes split as "Western Cattle Egret" but there are a couple of reports of the larger Asian subspecies B.i. coromandus from remote Midway and Tern Islands. Note the mostly dark bill of the juvenile bird (bottom). Such birds can easily be misidentified as other species.
References:
Cattle Egret (Bubulcus ibis), In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. retrieved from Neotropical Birds Online: https://neotropical.birds.cornell.edu/Species-Account/nb/species/categr
Hancock, J. & J.Kushlan. 1984. The Herons Handbook. Harper & Row, New York.
Martínez-Vilalta, A., Motis, A. & Kirwan, G.M. (2019). Cattle Egret (Bubulcus ibis). 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/52697 on 29 June 2019).
Pratt, H.D., Bruner, P., and Berrett, D.G. (1987) A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press.
Pyle, R.L., and P. Pyle. 2017. The Birds of the Hawaiian Islands: Occurrence, History, Distribution, and Status. B.P. Bishop Museum, Honolulu, HI, U.S.A. Version 2 (1 January 2017) http://hbs.bishopmuseum.org/birds/rlp-monograph/
Telfair II, Raymond C.. (2006). Cattle Egret (Bubulcus ibis), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/categr