There is an interesting thread evolving here, following the occurence of a 1cy Black-winged Kite in Nizzana, Israel. It was tentatively identified in the field as belonging to the African form caeruleus, based mainly on date and location (caeruleus breeds only 200 km west of Nizzana) and the secondaries looked pretty white in the field, though in some images they look grey.
From what I know, secondary pattern is the only feature separating caeruleus from vociferus. 'vociferus' or at least dark-secondaried Black-winged Kites have been recorded in Israel several times in recent years.
But after some discussions and net browsing, it seems that little is known or documented about the amount of variation within each form regarding secondary pattern in adults, needless to say in non-adults. Based on images found on the web, some adult Asian birds show white secondaries!
Who knows, maybe one day these two forms will be split from each other. Can someone shed some light on this issue for me, and help me decide whether to go and twitch it or not?