Geographical variation and vagrancy / range expansion of the Black-winged Kite

Some references have doubted the distinctiveness of race vociferus of the Black-winged Kite (Elanus caeruleus); however, W European birds (Spain), i.e. nominate caeruleus, possess rather pale (virtually white) underside to the secondaries, contrasting with the primaries (http://andalucianguides.blogspot.co.uk/2009/11/cranes-bonellis-eagles-black-winged.html), whereas those in S & SE Asia have this tract almost as dark as the outer part of the wing (http://orientalbirdimages.org/search.php?p=3&Bird_ID=859&Bird_Family_ID=&pagesize=1); at least some recent vagrants in E Arabia appear to be of the race vociferus (http://www.birdsofsaudiarabia.com/2012/03/black-winged-kite-dhahran-hills-first.html). See also: http://www.surfbirds.com/forum/showthread.php?10639-Black-winged-Kite-First-for-the-Eastern-Province-of-Saudi-Arabia