Resin-Barrier Maintenance as a Mechanism of Differential Predation among Occupants of Red-Cockaded Woodpecker Cavities

The endangered Red-cockaded Woodpecker (Picoides borealis) is a cavity-limited cooperative breeder that excavates cavities in living pines and maintains a resin barrier that repels rat snakes (Elaphe obsoleta and E. guttata), its principal predators. Heterospecific occupants of Red-cockaded Woodpecker cavities (cavity kleptoparasites) exacerbate the limitation of cavities. However, heterospecifics do not maintain the resin barrier, which deteriorates without upkeep. Thus, we predicted that heterospecific occupants of Red-cockaded Woodpecker cavities should suffer rates of nest predation higher than the Red-cockaded Woodpecker's. We compared the daily nest-survival rates of the Red-cockaded Woodpecker and two heterospecific occupants of its cavities, the Red-bellied Woodpecker (Melanerpes carolinus) and Great Crested Flycatcher (Myiarchus crinitus), in two forests in northern Florida. Results from both forests supported the differential-predation hypothesis. Although during incubation the three species' daily nest-survival rates were similar, the primary cause of failure was hatching failure for Red-cockaded Woodpeckers but predation for the two heterospecific occupants. During the nestling stage, daily nest success was significantly higher for Red-cockaded Woodpeckers than for Red-bellied Woodpeckers or Great Crested Flycatchers and similar for the latter two species (i.e., Red-cockaded Woodpecker » Red-bellied Woodpecker ≥ Great Crested Flycatcher); predators destroyed 3–6% of Red-cockaded Woodpecker nests and 21–37% of kleptoparasite nests. We hypothesize that rat snakes have an indirect positive effect on the Red-cockaded Woodpecker (increased cavity availability) by preying differentially on heterospecific occupants of its cavities.