Its taxonomy is confusing and remains unsettled. It has sometimes included the Torresian, yellowish and silver-tipped imperial pigeons as subspecies.[3] The widespread nominate subspecies of the pied imperial pigeon differs from all these by its plain white thighs and undertail coverts (though often with a dark spot at the very tip), and its narrowly dark-tipped bluish bill. For comparison, the other species' have black-spotted undertail coverts and thighs (spotting mainly near thighs in silver-tipped imperial pigeon), the bill of the Torresian imperial pigeon is greenish-yellow, and the bills of the yellowish and silver-tipped imperial pigeons are bluish at the base and yellowish at the tip. Furthermore, the yellowish imperial pigeon has a distinctive yellowish tinge to its plumage[3] (some pied imperial pigeons may also appear yellowish, but infrequently to the same extent), and the silver-tipped imperial pigeon has silvery-grey remiges.[4] However, the subspeciesD. b. melanura of the Moluccas, which usually is considered a subspecies of the pied imperial pigeon, resembles the Torresian imperial pigeon in bill, thighs and undertail coverts, but has a significantly broader black tail-tip.[4] Consequently, some have suggested it should be placed under the Torresian imperial pigeon, while others have suggested it should be considered an entirely separate species, D. melanura[4] (for which the name black imperial pigeon has been used – an unfortunate choice, as only the tail has significantly more black than the other members of this group, and the name black imperial pigeon usually has been used for D. melanochroa).[5] Yet others have considered melanura to be invalid, instead believing it only is a morph of D. b. bicolor, as both types can be found on some islands.[4]
^ abcBaptista, L. F., P. W. Trail, & H. M. Horblit (1997). Family Columbidae (Pigeons and Dovexs). pp. 60-243 in: del Hoya, J., A. Elliott, & J. Sargatal. eds. (1997). Handbook of the Birds of the World. Vol. 4. Sangrouse to Cuckoos. Lynx Edicions, Barcelona. ISBN84-87334-22-9
^ abcdCoates, B. J., & K. D. Bishop (1997). A Guide to the Birds of Wallacea. Dove Publications Pty. Ltd. ISBN0-9590257-3-1
^Gill, F., M. Wright, & D. Donsker (2009). IOC World Bird Names. Version 2.1. Accessed 03-07-2009