Oxyrhopus formosus Yellow-headed Calico Snake
Some other names for this species:
Formosa False Coral Snake
Santa Cruz Forest Reserve, Loreto, PeruJanuary 19, 2014
Yellow-headed Calico Snake (Oxyrhopus formosus)
This brilliantly colored snake was stretched across a branch about ten feet directly above the trail.

Here is a complete list of the herps I saw in the wild on my 2014 MT Amazon Expeditions trip.

Online references:
Printed references: