| Abstract: | Roadkill of monarch butterflies and other arthropods and roadside nectar plants were recoded across Texas in 100 m transects in the fall and spring from fall 2019 to spring 2021. Texas fall monarch roadkill data from this and previous studies was used to extrapolate roadkill across the state, identify monarch roadkill hotspots, and develop MaxEnt monarch roadkill niche models. Monarch roadkill in Texas was estimated at 1-3 million per year in 2016, 2018, and 2020, representing about 2.5% of the monarch overwintering population. Fall monarch roadkill in Texas hotspots reached 136 per 100 m. Hotspots were concentrated along washes of IH-10 between Sonora and Sheffield, and along coastal causeways from Point Comfort to Corpus Christi. Potential monarch roadkill mitigation methods were reviewed, and two specific implementation strategies were detailed and compared for cost effectiveness: 1) Direct mitigation through two-week seasonal monarch flight diverter Specialized Management Areas (SMAs) placed at five roadkill hotspots outside the 30 ft clear zone from the roadway that induce migrating monarchs to fly above the traffic, as has been successfully implemented for migratory purple crow butterflies in Taiwan 2) Indirect compensatory mitigation through roadside pollinator habitat SMAs placed at seven sites outside the 30 ft clear zone from the roadway that include protective barrier fencing, planted milkweeds and non-milkweed monarch-preferred nectar plants, and disturbance management. A preliminary 30 year life-cycle cost analysis estimated that flight diverter SMAs may cost |
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