Red-cockaded Woodpeckers (Picoides borealis) excavate resin wells in the immediate vicinity of roost and nest cavity entrances. Resin wells are worked regularly, resulting in a copious and persistent resin flow that coats the tree trunk, especially below cavity entrances. Red-cockaded Woodpeckers also scale loose bark from cavity trees and closely adjacent trees. These two behaviors result in smooth, sticky surfaces surrounding cavity entrances. Climbing experiments on cavity, scaled, and control trees using rat snakes (Elaphe obsoleta) demonstrate that these behaviors produce a resinous barrier that is highly effective in preventing predatory snakes from gaining access to active Red-cockaded Woodpecker cavities.
Rudolph, D. Craig; Kyle, Howard; and Conner, Richard N., "Red-Cockaded Woodpeckers vs Rat Snakes: The Effectiveness of the Resin Barrier" (1990). Faculty Publications. 450.