The Asian Koel (Eudynamys scolopaceus) is a large, long-tailed, cuckoo measuring 39–46 cm. 
The male Asian Koel is almost entirely glossy bluish-black, aside from its red eyes. 
The female has the same red eyes, but has a dark brown plumage that is heavily spotted (4th photo).
The male has a very loud call, something like "ko-el" ("el" is stressed), and repeats this all the time. 
You hear this call throughout Thailand.

This species is a brood parasite, depositing its eggs in the unattended nest of a host bird — usually a crow! 
The Asian Koel chick hatches before the host’s chicks and forces the remaining eggs out of the nest. 
This brood parasitism actually reduces the crow’s reproductive success and keeps its population in check.

1st, 2nd & 3rd photo: Klong Muang beach area, Krabi, Thailand, 22 January 2013
4th & 5th photo: Ayutthaya, Thailand, 19 December 2009