Host plants and landscape predict use of roadside habitat by breeding monarchs

Vegetation along roadside edges, while posing some risks, can also provide breeding habitat for monarch butterflies. We investigated how landscape and site‐specific factors affect the quality of roadsides as monarch breeding habitat. We surveyed more than 250 sites along roadsides throughout Minnesota for milkweeds, floral resources and monarch eggs and larvae. We found that milkweed distribution was affected by adjacent land use and geography, with milkweeds more likely to be present in roadsides adjacent to crop and grassland and the south and west of the state. The presence and density of monarch eggs and larvae were primarily driven by milkweed density, with the likelihood of monarch presence at each site increasing with milkweed density. The density of monarchs per plant increased in sites with lower densities of milkweed, suggesting that monarch eggs are concentrated more densely on fewer plants where milkweed is scarce and spread more thinly across plants where milkweed is common. Monarch density per milkweed increased as sites were farther from core grasslands, to the south, and on narrower roadsides, also suggesting use may be higher in areas with a scarcity of habitat. The density of monarch eggs and larvae was higher in mowed than unmowed milkweed. Our study suggests that roadside habitats effectively provide breeding locations for monarchs, regardless of adjacent land use type and even when distant to high‐quality natural areas. Our findings assist conservation practitioners in planning and managing roadside habitats for monarchs and other pollinators. Breeding monarchs in Minnesota roadsides were best predicted by milkweed abundance; milkweed was more likely adjacent to grasslands and croplands and in the south and west. Monarch density per ha and per plant was related to milkweed density and higher farther from core grasslands, in narrower roadsides and in southern Minnesota. Monarch density per plant was inversely related to milkweed density suggesting the importance of even sparse amounts of milkweed; monarch eggs and larvae were more abundant in mowed than unmowed milkweed.