Adult Male:
- Entirely black plumage with a deep bluish sheen.
Adult Female:
- Generally, a mottled pattern of pale black and white.
- Dorsum (back) a pale black-brown with blue and green iridescence and white mottling.
- Head slightly lighter and more rufous.
- White markings on the head are elongated into vertical streaks.
- White markings on the wings and tail transform into irregular horizontal bars.
- White underparts with faint black barring.
Juvenile:
- Entirely black plumage, but after the first molt, the head plumage approaches that of the female.
- Juvenile males retain the black plumage for a period before gradually transitioning to the adult male plumage.
- Red eyes.
- Gray-blue beak with a black base.
- Lead-gray legs.
Measurements:
- Wing: 190 – 220 mm
- Tail: 181 – 203 mm
- Tarsus (leg): 35 – 37 mm
- Bill: 32 – 34 mm
Distribution:
- The Common Cuckoo (Cuculus canorus) is found in Thailand, Laos, Cambodia, Vietnam, southeastern China, and Malaysia.
- In Vietnam, the Common Cuckoo occurs throughout the plains and midlands.
- During the winter, most birds migrate south, and they are rarely seen in northern Vietnam.
This fascinating parasitic species deserves further in-depth research in Vietnam.