Assessing the benefits of managed golden-winged warbler (Vermivora chrysoptera) nesting habitat for breeding monarch butterflies (Danaus plexippus) in the western Great Lakes

The monarch butterfly ( Danaus plexippus ) and golden-winged warbler ( Vermivora chrysoptera ) are two disturbance-dependent, migratory species that have both suffered from breeding habitat loss and degradation. Given the overlap in distribution and ecological needs, efforts to manage golden-winged warbler habitat may also benefit monarchs. In 2021, we surveyed monarchs, milkweed ( Asclepias spp.), nectar resources, and structural vegetation characteristics at 49 sites managed for golden-winged warblers (“GWWA sites”) in the western Great Lakes region. We compared our observations to data from nearby sites managed specifically for monarchs (“reference sites”) and assessed the influence of site and landscape characteristics on monarch (adult/immature) and milkweed presence within GWWA sites. Immature monarchs, adult monarchs, and milkweed were 22x, 5x, and 110x more abundant at reference sites compared to GWWA sites, respectively. At GWWA sites, the presence of immature monarchs was positively associated with floral abundance and the presence of immature monarchs and milkweed presence were both positively associated with proportion of emergent herbaceous wetland cover within 500 m and 1 km. Additionally at GWWA sites, immature monarch density increased with milkweed density. Lastly, the presence of adult monarchs was positively associated with size of treatment area. Implications for insect conservation : Our findings suggest that sites managed as golden-winged warbler habitat can contribute to monarch habitat goals. This will best be done by conducting conservation practices that increase milkweed and floral abundance (e.g., via supplemental plantings) and targeting sites with more semi-natural herbaceous cover (e.g., pastures, herbaceous wetlands), while still meeting golden-winged warbler land cover requirements.