Clay-colored Robin (Turdus grayi). This I call the "Mono-Duet", a double call in which the bird uses both syrinxes to make slightly different sounds - it took me a while to figure out that this wasn't two birds duetting.
Also known as the Clay-colored Thrush, this is the national bird of Costa Rica, where is is called Yiguirro. It ranges from Mexico to northern Colombia, here in the Canal Zone of Panama.