Butterfly migration from and to peninsular Florida

Abstract

Abstract. Migrating butterflies were monitored with traps for 10 years at a site in north peninsular Florida, to determine seasonal and annual variation in numbers and directions of flight. In the spring, 81–96% of the principal migrants, Phoebis sennae (L.), Agraulis vanillae (L.), Precis coenia (Hübner) and Urbanus proteits (L.), flew northward; in the autumn, 86–95% flew southward. Estimated mean net numbers of these four species flying northward in spring across each ENE‐WSW metre were 3, 6, 69 and <1 respectively; numbers flying southward in autumn were 222, 413, 37 and 146. During a 5‐year period, the ratio of highest to lowest seasonal migration for a species did not exceed 9.3. The average median date of spring migration was 27 March for P.sennae, 23 April for P.coenia, and 12 May for A.vanillae. The average median date of autumn migration was 2–5 October except for U.proteus, whose average date was 14 October. The autumn migratory period, as measured by the duration of the middle half of migration, was about 2 weeks in P.coenia and about 4 weeks in the other three species. Compared to previously reported butterfly migrations, the ones studied here were notably uniform in magnitude and regular in timing. These and other data suggest that 4 million or more of these butterflies migrate northward from peninsular Florida almost every spring and that 40 million or more migrate southward to peninsular Florida almost every autumn.