Learning bird calls is one of the most important things when it comes to finding and identifying birds. When birding in habitats with dense vegetation, detecting birds by call is often the only way to know that they are there and if you are trying to separate Leaf Warblers then it is essential to know their calls in many cases.
There are other birds, however, that have calls so pervasive that they cannot be missed, the calling of doves in many parts of the world, the harsh calls of gulls in many coastal areas around the world and for anyone who has ever visited Bangkok, Thailand, the call of Asian Koel is impossible to miss. The Koel is one of those onomatopoeic bird names, like European Cuckoo, where the name of the bird is inspired by the bird's call. Sometimes other birders incorrectly pronounce this bird's name as "Ko-ul" but if you listen to the call you will clearly hear that the correct pronunciation is more like "Ko-Ell" and in the Thai language it is known as "Ga-Wow".
You can listen to the call yourself as well as watch the bird in this short video -Asian Koel Call
If you listen to the birds in the video, you will notice that there are other calls distinct from the regular "Ko-Ell" call, these are alarm calls and agitated noises rather than the mating call.
Over the years I have received more emails from people asking me about the call they have heard from their Bangkok hotel room than any other bird-related question and if it is a verbal conversation I can give them the answer before they have even finished the question, so frequently do people ask because of the pervasive nature of Asian Koels in the city. In fact, Bangkok probably has the highest density of Koels within its range in Southeast Asia, with possibly Singapore matching it.
Asian Koel is a brood parasite, just like European Cuckoo, and I frequently see fledged young being fed by Siamese Pied Starlings and to a lesser extent Great Myna and Common Myna; I once saw a Red-billed Blue Magpie feeding a young Koel too. In the photos above you can see the male is completely black with a coral-coloured bill and red eye while the female has a much more cryptic brown, speckled plumage which is strange as being a brood parasite she does not have to remain camouflaged while sitting on a nest.
For those birders who have trouble remembering bird calls or find it hard to even hear the difference between the calls of some birds, Asian Koel is a nice, distinctive one, both visually and audibly, that everyone can deal with. Once heard, it is not easily forgotten.