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Saturday, December 16, 2017

Variation in Resin-well Construction as an Indicator of Predation Load and Breeder Experience in Red-cockaded Woodpecker Populations

ROY S. DELOTELLE AND ROBERT J. EPTING
 

DeLotelle and Guthrie, Inc., Gainesville, FL, USA
Environment Consulting & Technology
 

The pine forest of the southeastern coastal plain supports a rich assemblage of cavity nesting birds. Unlike some regions, most primary and secondary cavity nesters experience high rates of nest predation. Rat snakes (Elaphe spp.) are proficient tree climbers and are well-documented nest predators throughout the red-cockaded woodpecker’s (Picoides borealis) range. Nesting success of this species, however, is relatively high. This woodpecker is well-known for excavating cavities in living pine trees as well as excavating moderate to small holes or resin wells above and below its cavities, and scaling loose bark from around them. These behaviors create a surface around the cavity entrance that is difficult for snakes to climb. Despite these protective behaviors, snakes successfully depredate some nests. This suggests that variation may exist in individual woodpecker investment in cavity protective behaviors. To explore the usefulness of resin-well construction on cavity trees as an indicator of predation and experience, we quantified variation in the resin-well barrier in five woodpecker populations in peninsular Florida. The extent of resin-well construction and redrilling varied by community type and cavity tree location. A pronounced seasonal increase in resin-well construction occurred on nest trees (the male roost tree) as nestlings aged across all community types. Cavity trees used by females showed a modest increase in resin-well construction from the winter to nesting. This increase in resin-well construction on nest trees was an indication of the risk to snake predation and the experience of breeding males, but not group size. There was, however, an increase in resin-well construction by first-year breeding males that had previous brood rearing experience as a helper compared to first-year breeding birds with no prior helping experience.


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