a1. Entire upper and under parts uniform gray.
b1. Smaller; wing, 157 mm.; tail, 119. ... mindorensis (p. 483)
b2. Larger; wing, 170 mm.; tail, 142. ... guillemardi (p. 481)
a2. Upper and under parts not entirely uniform.
b1. Throat and breast uniform gray; belly and under parts barred
with black and white.
c1. Lower back, rump, and upper tail-coverts barred with black.
d1. Feathers of rump dark gray, barred with black and fringed
with whitish; general color of upper parts and breast darker
gray; black bars on the belly and flanks as wide as, or wider
than, the white interspaces, giving these parts a much blacker
appearance; under tail-coverts with wide bars of black and white,
the former being rather wider. ... striatus (p. 482)
d2. Feathers of rump white, barred with black; general color of
upper parts and breast paler gray; black bars on the belly and
flanks much narrower than the white interspaces, giving these
parts a whiter appearance; under tail-coverts white, with one
or two narrow wide-set black bars. ... difficilis (p. 480)
c2. Lower back, rump, and upper tail-coverts uniform gray like
the back. ... cebuensis (p. 484)
b2. Entire under parts barred with black to the throat; rump and
upper tail-coverts barred with black.
c1. Under tail-coverts widely barred with black and white,
the black bars being as wide as the white interspaces; patch of
feathers covering the nostrils gray like the rest of the crown;
general color of the throat and breast gray, barred with black,
contrasting with the black and white belly; black bars on the
belly and under parts very wide. ... panayensis (p. 483)
c2. Under tail-coverts either pure white, or white with some
black bars; patch of feathers covering the nostrils whitish;
general color of throat and breast white, barred with black like
the rest of the under parts; black bars on the belly and under
parts narrower. ... kochi (p. 482)