Regional abundance and local breeding productivity explain occupancy of restored habitats in a migratory songbird

Ecological restoration is a key tool in offsetting habitat loss that threatens biodiversity worldwide, but few projects are rigorously evaluated to determine if conservation objectives are achieved. We tested whether restoration outcomes for an imperiled bird, the Golden-winged Warbler (Vermivora chrysoptera; GWWA) met the assumptions of the 'Field of Dreams' hypothesis or whether local and regional population dynamics impacted restoration success. From 2015 to 18, we surveyed 514 points located in recently restored successional habitats. We used new- and published data on the survival of 341 nests and 258 fledglings to estimate GWWA breeding productivity. Occupancy and colonization of restored habitats were significantly higher in our Western Study Region (Minnesota and Wisconsin) than our Eastern Study Region (Maryland, Pennsylvania, and New Jersey), a pattern that mirrored broader regional population trends. At local scales, productivity was high in Eastern Pennsylvania (> 3 independent juveniles/pair/year) but low in Central Pennsylvania (1 juvenile/pair/year) while both Western and Central Minnesota hosted intermediate productivity (between 1 and 2 juveniles/pair/year). Productivity and occupancy covaried locally in the Eastern Study Region, while occupancy was high in the Western Study Region, despite intermediate productivity. These differences have profound implications for restoration outcomes, as GWWA possessed robust capacity to respond to habitat restoration in both regions, but this capacity was conditional upon local productivity where the species is rare. Our findings suggest that, even when restoration efforts are focused on a single species and use comparable prescriptions, interactions among processes governing habitat selection, settlement, and productivity can yield variable restoration outcomes.