The Pacaus bird snake is the Pacauan Whistler's most important predator.
The Pacuan bird snake, Avanguis pacausus, is an elapid from the Pacaus islands with markings on its head.
It is one of the most active and vicious snakes of the archipelago.
The pattern on its face is mimicked by the tail of the terratail.
It and its relatives' ancestors had rafted to Pacaus from Australia or the other islands in that corner of the Pacific at one time or another.