We heard the quetzals before we saw them. Their resonant, yelping call notes emanated from high in the ancient trees bordering the trail. At first, I only got frustrating glimpses of the birds' iridescent green back and throat as the small flock fed on wild avocados in the thick foliage. My guide, Jason Lara, then drew my attention to a male that had hopped up onto a branch in full view. I could barely contain my excitement. The helmet-like crest, bright red belly and ridiculously long upper tail coverts sparkled in the dappled light. Seconds later, when the quetzal flew off, the coverts trailed behind the bird like the train of a wedding dress. I immediately understood why this species rates among the most beautiful in the world.