Falco æruginosus Linnæus, Syst. Nat. ed. 10 (1758), 1, 91.
Circus æruginosus Sharpe, Cat. Birds Brit. Mus. (1874), 1, 69;
Hand-List (1899), 1, 246; Blanford, Fauna Brit. India Bds. (1895),
3, 387; Grant, Ibis (1895), 438; Oates, Cat. Birds' Eggs (1902),
2, 239; McGregor and Worcester, Hand-List (1906), 41.
Cagayan Sulu (Mearns); Luzon (Whitehead); Mindoro
(Everett). Temperate Europe and Siberia; in winter to northern
Africa, Indian Peninsula, and China.
"Adult male.--Head, neck, and breast buff or pale rufous, with dark
brown shaft-stripes, broader on the breast; back and most of the
wing-coverts dark brown; scapulars still darker, sometimes gray toward
the base; smallest coverts along the forearm whitish, with dark brown
shafts; outer greater coverts, primary-coverts, and all quills except
first six primaries dark silvery gray, remaining coverts and very
often the tertiaries dark brown; first six primaries black with the
basal portion white; upper tail-coverts white with rufous and brown
mixed in various ways; tail gray above, isabelline below; abdomen
and lower tail-coverts ferruginous brown, more or less striped darker.
"Females are dark brown except the crown, nape, chin, and more or less
of the throat, which are buff with brown stripes. There is sometimes
a patch of buff on the breast, the wing-coverts and back have buff
edges, and the upper tail-coverts are rufous.
"The young of both sexes resemble the female, except that the buff
on the head is sometimes unstreaked and more limited in extent, being
confined in some cases to a nuchal patch or even wanting altogether.
"'Bill black; cere and base of bill greenish yellow; iris
yellow, brownish yellow in females and young; legs and feet rich
yellow.' (Hume.)
"Length of males, 533; tail, 241; wing, 406; tarsus, 86; length of
females, 572; tail, 248; wing, 419; tarsus, 89." (Blanford.)
The measurements given by Sharpe are as follows: "Male, length, 571;
culmen, 39; wing, 406; tail, 254; tarsus, 86. Female, length, 584;
wing, 432; tail, 279; tarsus, 96."
The young of Circus spilonotus and C. æruginosus are similar in
plumage and as the size is also nearly the same it is a matter of
some difficulty to distinguish between them. Sharpe identified
as C. æruginosus a young female collected in the Philippines by
Cuming, but he finally referred it to C. spilonotus. Whitehead
obtained an immature male in northern Luzon which according
to Grant "is undoubtedly referable to the present species
[æruginosus]." Concerning the specimen from Calayan Sulu, collected
by Mearns, Dr. Chas. W. Richmond writes that "it may prove to be
spilonotus." Hartert makes no comment on the specimen collected by
Everett in Mindoro.
Some of the numerous brown marsh hawks in the Bureau of Science
collection may be of this species but they can not be determined
at present.
Genus ASTUR Lacépède, 1799.
Bill small and compressed, upper mandible with a deep notch or a
strong sinuation near its tip; first primary short, third or fourth
longest; tarsus rather long and with transverse plates in front and
behind but the division lines between plates very obscure.
Species.
a1. Larger, length more than 330 mm.; under parts white, barred with
brown or pale rufous. ... trivirgatus (p. 216)
a2. Smaller; length less than 330 mm.; under parts not barred.
b1. Breast light chestnut. ... soloensis (p. 217)
b2. Breast light gray. ... cuculoides (p. 218)