Meteorological Conditions and Flight Speed during Observed Eastern Monarch Fall Migration Events

The abundance of the monarch butterfly (Danaus plexippus) in overwintering habitat has decreased over the past few decades. We investigated how meteorological conditions (temperature and precipitation) and flight speed affect the fall migration of marked and live-resighted Eastern North American monarch butterflies to better understand how climate change may affect their migration. We factorially simulated a range of flight speeds and maximum and minimum temperatures during migration for individual butterflies whose full live capture history was known. Within the allotted dates and time between marking and recapture, we used data from the nearest meteorological stations along the migration route that minimized the distance to recapture locations, to determine the flight speed and maximum and minimum temperature that monarchs use during fall migration. The mean flight speed that optimized the model for individual butterflies was 7.50 ± 5.00 km/h. The thermal conditions best fitting migration ranged from a mean minimum of 7.67 ± 5.42 °C to a mean maximum of 25.2 ± 4.73 °C. The low estimated upper temperature suggests that an increase in temperature due to climate change and an accompanying increase in metabolic demand, may reduce successful fall migration to overwintering sites, overwintering, or remigration the following spring.