We heard this bird calling, and two others responding from a distance, for a long time before we saw it right at the edge of the trail. He was most cooperative and not at all alarmed as we slowly crept to within a very close distance. Something of an exhibitionist but who can blame such a wonderful bird! Ben King correctly describes the call as "far carrying musical kwow-wow".
PS. Whoops, I initially posted the wrong image. Corrected 9 Feb.