Immature male.--Upper parts earthy brown, lighter on crown, the feathers tipped with white; forehead all white; long crest-feathers blackish brown; a black patch in front of and over eye; wing-coverts like the back; primaries and secondaries blackish brown, tipped with white; tail blackish brown, tipped with white and crossed by about nine lighter bars; entire under parts, except a brown patch on each flank, pure white. Wing, 370; tail, 225; culmen from base, 35; tarsus, 69; middle toe with claw, 72.
The sexes are similar in color. A male from Sibuyan measures: Wing, 340; tail, 190; culmen from base, 34; tarsus, 72. A female from northern Mindanao measures: Wing, 360; tail, 210; culmen from base, 35; tarsus, 66.
Bill compressed; culmen rapidly curved from base to tip; edge of upper mandible sinuate; nostril large and oval; occipital crest short and slightly pointed; wings moderate, fourth or fifth quill longest; secondaries long, falling short of primaries by about length of middle toe without claw; tarsus covered to the toes with short thick-set feathers; top of toes covered with small irregular scales.
a1. Under parts white with bold brown markings on breast; thighs brown with fine white cross-bars. ... philippensis (p. 224) a2. Under and upper parts uniform blackish brown. ... limnæëtus (p. 225)
Spizaetus philippensis Gurney, in Gould's Birds Asia (1863), pt. 15. Spizaetus philippinensis Sharpe, Cat. Birds Brit. Mus. (1874), 1, 261 (footnote). Limnaëtus philippensis Walden, Trans. Zool. Soc. (1875), 9, pt. 2, 141, pl. 24. Spizaëtus philippinensis Sharpe, Hand-List (1899), 1, 264; McGregor and Worcester, Hand-List (1906), 42.
Basilan (Steere Exp., Bourns & Worcester); Luzon (Gevers, Heriot, Whitehead); Masbate (Steere Exp.); Mindoro (Porter); Negros (Everett, Steere Exp.); Palawan (Platen); Siquijor (Bourns & Worcester).
"The general color of the upper surface in this species is a dark umber-brown; but the base of the feathers of the crest is white and the margins of the other occipital feathers are of a light yellowish brown. Some of the scapulars and other alar feathers (especially the latter) are slightly tipped with the same; the tail, which is of a somewhat lighter brown than the back, is tipped with a very narrow edging of white, and is also crossed by seven blackish brown bars, the upper one, however, being somewhat indistinct, and the two lower being separated by an interval which is twice the breadth of the spaces between the other bars. The throat has a broad blackish band running down the center, with two similar and nearly parallel bands proceeding from the corners of the mouth, the three bands all merging in a cluster of dark brown lanceolate marks upon the upper portion of the breast, the intervals between these markings, and also the whole sternal and abdominal regions, being tinged with a yellowish rufous; the under tail-coverts are barred with brown and white, the former bars being much broader than the latter; and the thighs and tarsi are marked throughout their length with narrow, equidistant, transverse bars of the same color. Length, 635; crest, 63; wing, 375; tail, 292; tarsus, 89; middle toe with claw, 76." (Sharpe.)