Rasmussen & Anderton (2005) suggest that the Cattle Egret (Bubulcus ibis) is actually two species, Bubulcus ibis from Africa and the Americas, and B. coromandus from southern and eastern Asia to Australasia. Natural expansion of their ranges from Africa and Asia respectively occurred recently. Although HBW and BirdLife International have not split this species, they suggest Western Cattle Egret and Eastern Cattle Egret, respectively, as names for the potential new species (del Hoyo & Collar 2014). These names also appear on the IOC World Bird Names list (doi : 10.14344/IOC.ML.4.1). Unlike north/south designations, east/west names only make sense from a given location or within a single continent or region. From a global perspective, they are meaningless because they depend on where the observer is standing. For example, for islands in the Pacific Ocean, "Eastern" Cattle Egrets would be found in the west, and "Western" Cattle Egrets in the east! I recommend that we use "African" and "Asian" for these forms respectively, which designate their historical origin, and are unambiguous regardless of where one stands.
These comments would also apply to any other splits that involve species with global ranges, such as Barn Owls and Osprey, and to reef-egrets (there is Western, but no Eastern, and it occurs mainly on the east coast of Africa; better to call it Indian as an equivalent to Pacific).
Del Hoyo, J. & Collar, N.J. (2014). HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions, Barcelona.
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.