a1. A large terminal white spot on tail.
b1. Larger, length about 290 mm.; a larger terminal white spot across
both webs of outer rectrix; spot on first primary white and larger,
on second primary extending to the shaft. ... macrurus (p. 348)
b2. Smaller, length about 250 mm.; a smaller terminal white
spot across inner web of outer rectrix; spot on first primary
buff and smaller; on second primary not extending to the
shaft. ... manillensis (p. 346)
a2. No terminal white spot on tail which is barred and mottled.
b1. Smaller; wing less than 180 mm.; spots on primaries much larger,
whitish and unspeckled. ... griseatus (p. 344); mindanensis (p. 346)
b2. Larger; wing more than 190 mm.; spots on primaries much smaller,
buffy and speckled with brown. ... jotaka (p. 349)