Structurally this genus only differs from Cuculus in having rather shorter wings, with the primaries extending from one-fifth to one-third the length of the closed wing beyond the ends of the secondaries ; sometimes the third primary is longest, sometimes the fourth. The Coloration is remarkable, even amongst Cuckoos, for its close imitation of Hawks and Falcons ; not only is the adult garb Accipitrine in character, but the plumage of the young resembles that of several immature birds of prey. The resemblance in plumage and flight to Hawks is quite unexplained, though, as it is sufficient to cause great alarm to small birds in general, it is probably connected with breeding-habits.
In all species of Hierococcyx the tail is broad with distinct dark cross-bars ; the plumage above is uniform or nearly so in adults, mixed with rufous bars in the young; below it is spotted in the young, but generally becomes nearly uniform or transversely banded in the adult stage. Sexes alike.
This genus ranges throughout Eastern Asia from Siberia to India and the Malay Peninsula; it is also found in all the Malay islands. Pour species inhabit India or Burma.
Key to the Species.
a. No distinct dark cheek-band from the eye.
a1. Abdomen transversely banded in adults.
a2. Back in adults brown : wing over 8.5……………….H. sparveroides, p. 211,
b2. Back in adults ash-grey: wing 7 to 8……………….H. varius, p. 213.
b1. Abdomen never banded; back in adults blackish grey: wing 6.7 to 7.4……………….H. nisicolor, p. 214.
b. A distinct dark cheek-stripe……………….H. nanus, p. 215.