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.