POPULATION ECOLOGY Butterfly Migrations in Florida: Seasonal Patterns and Long-Term Changes

Flight traps atGainesville, innorth-centralFlorida, operating from1984 to spring2000, separated butterßies migrating into the Florida peninsula (SSE 90 ) from those migrating out of the Florida peninsula (NNW 90 ). Five species ßew southward in the fall and northward in the spring: Phoebis sennae (L.), Agraulis vanillae (L.), Junonia coenia (Hübner), Urbanus proteus (L.), and Eurema lisa (Boisduval & LeConte). Five species had signiÞcant northward ßights in spring but no signiÞcant migration in fall: Pieris rapae (L.),Vanessa virginiensis (Drury),Vanessa atalanta (L.), Eurytides marcellus (Cramer), and Libytheana bachmanii (Kirtland). Danaus plexippus (L.) had a southward ßight in fall but no signiÞcant migration in spring. Eurema daira (Godart) switched from a net movement northward in early fall to a net movement southward in late fall, whereas Eurema nicippe (Cramer) maintained a net movement northward throughout the fall. The major migrants differed signiÞcantly in the seasonal timing and duration of peak migration. When the numbers trapped were greatest, the proportion of those ßying in the migratory direction was greatest. The numbers of springmigrants ofA. vanillae increased during the course of the study, whereas both the spring and fallmigrations of J. coeniadeclined.The fallmigrations ofP. sennae andU. proteusdeclined sharply. In 1990Ð1999, the fall migrations of P. sennae and U. proteus averaged only 37 and 15% of what they had averaged in 1984Ð1989. Reduced planting of soybeans in source areas for migrants probably contributed to these steep declines.