Do Red-cockaded Woodpeckers Select Cavity Trees Based on Chemical Composition of Pine Resin?
We examined resin chemistry of loblolly (Pinus taeda) and shortleaf (P. echinata) pines selected as cavity trees by Red-cockaded Woodpeckers (Picoides borealis) in eastern Texas. We sampled resin from (1) pines selected by Red-cockaded Woodpeckers that contained naturally excavated active cavities, (2) pines selected by forest biologists that contained artificially installed cavity inserts and were actively being used by Red-cockaded Woodpeckers, and (3) control pines of similar age and appearance to the active cavity trees. We hypothesized that if woodpeckers are inducing a change in resin chemistry by excavating resin wells, this change should appear in active cavity trees selected by woodpeckers and trees selected by biologists, but not in control pines. If woodpeckers are selecting pines that have specific resin chemistry, concentrations of some resin components in active cavity trees selected by the woodpeckers for natural cavity excavation should be different from both control pines and pines selected by biologists. A large diterpene acid peak containing an isopimaric-levopimaric-palustric methyl-ester mix in active natural cavity trees was approximately 20% greater than controls and 22% greater than trees with artificial cavities. None of the other eight resin chemicals differed among treatments. The activity of Red-cockaded Woodpeckers at resin wells did not appear to affect the composition of cavity tree resin. Woodpeckers, however, may select pines with specific resin chemistries for cavity trees.
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