Can roadside habitat lead monarchs on a route to recovery?
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The Eastern North American monarch butterfly population has severely declined over the past decade. The decreasing availability of larval host plants (milkweeds) due to the use of herbicide-tolerant crops has been implicated in this decline. Roadsides could provide additional habitat for monarchs. In this study we document the occurrence of milkweed and monarchs on roadsides, and discuss whether roadsides are appropriate targets for monarch habitat restoration. We sampled roadside rights-of-way in the Upper Midwestern U.S. during the summer of 2015 to estimate the abundance, distribution, and diversity of milkweeds and the extent to which monarchs use these milkweeds. We then compared monarch densities in roadsides to other habitat types and modelled immature monarch densities based on several site characteristics. Our findings suggest that roadsides have conservation potential for monarchs, especially when other habitat is scarce and if wildlife-friendly management practices are enacted. Milkweeds were found on ~60% of roadside transects. Asclepias syriaca was the most common of the seven species encountered, occurring on 97% of transects with milkweed. Immature monarchs were observed in roadsides, but in lower densities than other habitats during the same time period. At lower milkweed densities, immature monarch density per unit area is positively correlated with milkweed density. However, milkweed density weakens as a predictor of immature monarch density over ~0.6 plants per m2, possibly indicating a saturation effect.
KeywordsMonarch butterfly Milkweed Roadside habitat Conservation Habitat corridor
We thank Wayne Thogmartin and the United States Geological Survey for providing GIS support and selecting sampling points to initiate our study. A special recognition goes to University of Minnesota Monarch Lab members Dane Elmquist, Cora Lund Preston, and Joe Miller for their support and company in the field. We thank all of the MLMP volunteers as well as coordinators from the U of M Monarch Lab, who go beyond their normal duties to ensure the continuance of this project. We are grateful for staff from Monarch Joint Venture and Monarch Net for providing valuable expertise and resources. Funding was provided by Environmental Stewards in conjunction with the USGS and AmeriCorps to KK and a National Science Foundation Graduate Research Fellowship (00039202) to CS.
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