We developed Habitat Suitability Index (HSI) models to assess habitat quality for 40 priority bird species in the Central Hardwoods and West Gulf Coastal Plain Bird Conservation Regions. The models incorporated both site and landscape environmental variables derived from one of six nationally consistent datasets: ecological subsections from the National Ecological Unit Hierarchy, National Land Cover Dataset, National Elevation Dataset, National Hydrography Dataset, State Soil Geographic Database, and Forest Inventory and Analysis data. The models were verified by comparing subsection-level HSI scores and Breeding Bird Survey (BBS) abundance via Spearman rank correlation (HSI gen tech report PDF and HSI validation PDF).
We set population objectives for our priority species following the categories used in the Partners in Flight Landbird Plan (PIF Landbird Conservation Plan 2004), but based our BCR objectives on trend data specifically for the Central Hardwoods Bird Conservation Region (BCR) where possible. Density estimates were scaled to habitat quality on a scale of 0 – 1, assuming a linear relationship with habitat suitability.
Species-specific habitat objectives were then calculated by estimating the extent of natural community restoration efforts necessary to provide enough habitat for the total population objective (i.e. existing birds and additional birds) of each priority species (21 of 38) for which we had a validated HSI model. This calculation was structured to balance the relative suitability of each natural community used by the species against the relative potential to restore each natural community (Setting Population and Habitat Objectives for Forest-associated Birds in the Central Hardwoods Bird Conservation Region .
Species-specific habitat objectives were allocated geographically (state portions of the BCR) based on the relative restoration potential of each natural community in each state. Two sets of BCR-level habitat objectives were derived from the species-specific objectives. The Minimum BCR Objective was calculated as the maximum natural community areas needed by a species in a state for a suite of 10 Continental Priority (i.e. Watch List) species. The Maximum BCR Objective was calculated in the same way but for the full suite of 21 species of continental and regional priority, (See CHJV Forest and Woodland Implementation and Habitat Objectives by states.) The minimum objective called for 4.8 million acres of restoration, or 12.4% of land currently classified as forest in the National Land Cover Dataset; the maximum called for 10.5 million acres or 27.1% of land currently classifies as forest.
The HSI models and density estimates for three species under current conditions and desired natural community restoration scenarios were later linked with a BCR-wide population viability model to determine if our habitat restoration targets would result in the predicted population response. Results indicated that Worm-eating Warbler was at or near carrying capacity; Wood Thrush populations would benefit most by an increase of survival during the non-breeding period, indicating that habitat work on the breeding grounds was less important than thought in achieving the desired outcome; and that Prairie Warbler would benefit from habitat conservation both on the breeding grounds as well as increases in survival during the non-breeding season (Bonnot et al 2011 and Bonnot et al 2013). These results indicate that habitat objectives based simply on increasing carrying capacity on the breeding grounds aren’t always the appropriate metric for guiding conservation efforts at our BCR-scale.