There are over thirty subspecies of this heron world wide. The buffy fringed wing coverts combined with medium gray neck are characters of the race chloriceps of the Indian mainland and Sri Lanka. This race is synonymized with B. s. javanica by some authors. The latter is said to average darker gray and have longer mustache stripes but these features may vary individually.
This species is a close relative of North America's Green Heron (Butorides virescens). Both are small, compact herons, quite similar in appearance. They were formerly lumped under the name Green-backed Heron, and the recently published HBW Illustrated Checklist reverts to that treatment as does Birdlife International. They adopted the Tobias scoring system in which the Green Heron gets a score of five, while a score of seven is needed to split. They also have a rather odd way of interpreting the zone of overlap and hybridization in Panama in which Green Heron gains only two "species points." I think a more conventional BSC interpretation would grant Green Heron full species status because of the relatively high percentage of non-hybrids in the contact zone. Their point that splitting Green Heron leaves South American populations conspecific with old world taxa is valid, but their opinion that such an arrangement is "improbable" would benefit from further explanation because their adopted taxonomic arrangement does the same "improbable" thing.
Some authors include this species in the genus Ardea but Butorides differs in a number of ways including having no distinct breeding plumage. Canon PowerShot SX50 HS
References:
Ali, S & SD Ripley (1987). Compact Handbook of the Birds of India and Pakistan. Edition 2. Oxford University Press.
Hayes, F.E., Weidemann, D.E., Baumbach, D.S., Tkachuch, R.D. & Tkachuch, C.M. (2013) Variation and hybridization in Green Heron (Butorides virescens) and Striated Heron (B. striata) in central Panama, with comments on species limits. North Amer. Birds 67(1): 4–8.
Martínez-Vilalta, A., Motis, A., Christie, D.A. & Kirwan, G.M. (2016). Green-backed Heron (Butorides striata). 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 http://www.hbw.com/node/52704 on 22 June 2016).
Rasmussen, P.C. & Anderton, J.C. (2005) Birds of South Asia. The Ripley Guide. Vols. 1 and 2. Smithsonian Institution & Lynx Edicions, Washington, D.C. & Barcelona.