Grande Comore Blue Vanga (Cyanolanius comorensis ssp. bensoni Louette & Herremans)
This taxon, described in 1982, is thought to inhabit, or to have inhabited, the island of Grande Comore, Comoros in the Indian Ocean; it is, however, known from only a single somewhat doubtful specimen that was collected as late as 1981.
Here is an excerpt from the original description.:
“In bill length intermediate between C. m. madagascarinus and comorensis; total culmen 18.5 mm as against an average of 17.3 in both sexes of madagascarinus and 20.1 mm in both sexes of comorensis. Bill decidedly more robust than in madagascarinus, although not much longer. In plumage in all respects seemingly nearest to comorensis although there is no similar aged specimen of this race available.“
“Apart from the diagnosis of bensoni, the following is a fuller description of the holotype (not fully adult):- Upperparts lilac blue, crown somewhat darker, with a few bright blue (adult) feathers appearing on crown and mantle. Inner webs of inner secondaries blue, like outer webs (like comorensis, inner webs not black as in madagascarinus). Underparts white, a few buffish feathers on flanks. Black mask just starting to appear. Tail feathers with square tips, not pointed as in very young specimens of Cyanolanius, and with buffish fringes. Iris pale blue. Legs grey-blue. Bill with pale base to both mandibles, tips dark. One may conclude that bensoni agrees well with comorensis in plumage characteristics but has a definitely less robust bill, intermediate in size between the 2 other races. Some doubt may persist as to the bill size in the adult, but I have measurements from 4 immatures of madagascarinus (mounted) in RNL, certainly somewhat younger than the holotype of bensoni, averaging 17.1 (versus 17.3 in the adult, see above) showing that this possible difference is insignificant.”
This sole specimen may represent a stray from the nearby island of Mohéli, which is home to the nominate race of the Comoros Blue Vanga (Cyanolanius comorensis (Shelley)), or it may indeed constitute a member of a distinct endemic population. If there indeed ever was a population of Blue Vangas living on Grande Comore, it must now be extinct.
There is also another mystery – why are there no Blue Vangas to be found (at least today) on the islands of Anjouan and Mayotte which in fact lie between Mohéli and Madagascar?
 M. Louette; M. Herremans: The Blue Vanga Cyanolanius madagascarius on Grand Comoro. Bulletin of the British Ornithologists’ Club 102(4): 132-135.1982