I suspect that there are at least four individuals. I have definitely seen two males, a female, a (possible) juvenile and heard at least one other calling in the distance. I have heard Koels calling in this area for the last five years or so but have rarely seen them till this year, when they have been (frustratingly) in a neighbour's oak tree or else my back yard or very close by, but they are usually very well camouflaged.