LAUSR

Abstract Urban rights-of-way (ROWs) offer large underused tracts of land that could be managed for plants and butterflies of threatened ecosystems like tall-grass prairies. However, built-up unvegetated urban lands might serve as barriers preventing butterflies and resource plants from settling along ROWs. Further, negative edge effects from surrounding urban lands or frequent mowing and spraying associated with urbanization may prevent butterflies from benefiting from urban ROWs as habitats. However, because ROWs often run for kilometres, they might facilitate movement from other, similar habitats by which they run close. To determine if surrounding built-up lands had a greater effect on butterflies than did the abundance of resource plants along ROWs, we surveyed butterflies and resource plants along transects in 48 transmission lines in or near Winnipeg, Manitoba, 2007–2009. In general, butterfly richness and abundance were better predicted by available resources than by built-up urban lands surrounding ROWs. Butterfly species richness per visit increased by 85% with increases from 10 plant species per site to 80 species of plants per site, while abundance per species per visit increased by 100% with increases from negligible forb cover to 5% forb cover, and by 112% with increases in vegetation height-density from 5 cm to 40 cm high. If appropriate resource plants are reintroduced and managed for along urban ROWs, densities of most butterfly species will increase along these lines despite surrounding built-up urban lands. Thus, urban ROWs present an opportunity for restoring habitats for prairie butterflies.