The influence of habitat patch size, isolation, and condition on Pileated Woodpecker occupancy in southwestern Ohio

Background/Question/Methods

Previous studies have shown that Pileated Woodpeckers (Dryocopus pileatus) prefer large wooded areas (> 100 ha) for inhabitance.  However, few studies of D. pileatus have been done in the eastern United States and none in Ohio, more specifically, southwestern Ohio where agriculture is prevalent and forests are significantly fragmented.  Therefore, forest isolation may serve as an important habitat characteristic for Pileated Woodpeckers since they are more vulnerable to predation when outside the confines of a dense canopy.  The objective of this study was to determine the forest fragment size, isolation, and composition preferred by Pileated Woodpeckers for breeding habitat.

We determined relative abundance of D.pileatus by counting excavated cavities.  We sampled 40 forest fragments varying in size and isolation for Pileated Woodpecker cavities and forest characteristics within 25 x 50 m plots.  We characterized the forest structure and composition of the stand by using the point-center quarter method within each rectangular plot and used ArcGIS10 to process LiDAR remote sensing data to analyze forest complexity and to process stand isolation.  We hypothesized that Pileated Woodpecker relative abundance would increase with forest fragment size and density of large old, moribund, or dead trees, but decrease with isolation.   

Results/Conclusions

A linear model including the three explanatory variables snag density, basal area, and site size revealed significant impacts of snag density (p = 0.03, R² = 0.28) on Pileated Woodpecker cavity density but no significant impacts of basal area (p = 0.41, R² = -0.002) and site size (p = 0.07, R² = 0.20).  Additionally, correlation tests did not reveal a significant correlation between cavity density and forest stand isolation.  In conclusion, we had to reject the hypothesis that size and isolation of a forest fragment in southwestern Ohio influences Pileated Woodpecker habitat choices.  However, forest characteristics such as snag density, directly relating to Pileated Woodpecker ecology in the form of food and shelter requirements, showed the predicted association with this woodpecker's activity.