Broad-billed Motmots (Electron platyrhynchum) sound like a shortened train whistle to me. The sound is unmistakable. This one was recorded at La Selva (Costa Rica), 11/98.
Blue-crowned Motmot (Momotus momota) - Recorded at Rancho Oropendola near Orotina (Costa Rica) - this bird repeats this "bark" every 5 seconds or so over and over. Motmots are beautiful birds with long, knob-ended tails, which they swing back and forth side-to-side like a pendulum. The tail feathers emerge without the "knobs", but the barbs abrade off quickly in the area a few cm proximal to the end, leaving a "knob" attached only by the shaft.
Here is a duet performed by a pair of Blue-crowned Motmots (Momotus momota) in the forest near Cabinas el Bosque, Monteverde (Costa Rica) - morning of 6/16/99.
