ABSTRACT: The Kirtland’s warbler (Setophaga kirtlandii) was delisted officially after more than 50 years of conservation and management activities following initial listing under the U.S. Endangered Species Preservation Act in 1966. Expanding their nesting habitat is a key element in continuing conservation actions outlined by the Kirtland’s Warbler Conservation Team. To this end, we used known characteristics of jack pine ecosystems suitable for nesting Kirtland’s warblers to identify potential breeding habitat expansion opportunities across Wisconsin and Michigan's Upper Peninsula. First, we overlaid Kirtland’s warbler 2000-2018 census locations within the study area with LANDFIRE (2014) Environmental Site Potential (ESP) data to identify the categories with greatest historical warbler occupancy. ESP data were used because it provided consistent ‘wall-to-wall’ coverage for the entire study area and focused on potential habitat development areas rather than existing cover types. The resulting categories were Boreal Jack Pine-Black Spruce Forest, Laurentian-Acadian Northern Pine(-Oak) Forest, and Laurentian Pine-Oak Barrens. The raster cells of the three ESP categories were then combined into a single spatial distribution of potential nesting habitat opportunities. Because Kirtland’s warblers are area-sensitive, we retained only those patches greater than 50 acres. Next, we refined this habitat distribution by overlaying soil data (NRCS SSURGO soil survey) to refine potential habitat opportunities to areas with Excessively-Drained Dominant Component (very sandy) soils because Kirtland’s warblers are ground nesters preferring young, dense jack pine forests growing on nutrient poor, well-drained soils (Byelich et al. 1976). Last, we integrated land ownership (public and private) to enhance public-private partnerships for habitat management to create larger nesting habitat complexes that could be maintained in the future on a rotating basis ensuring enough young jack pine forests are on the landscape to help sustain the conservation goal of 200 Kirtland’s warbler pairs nesting outside of their core breeding area in northern Lower Michigan.

- Byelich, J., W. Irvine , N. Johnson , W. Jones , H. Mayfield , R. Radtke , and W. Shake . 1976 . Kirtland's Warbler recovery plan. U.S. Fish and Wildlife Service , Washington, D.C.