ORIENTATION OF FALL-MIGRATING BUTTERFLIES IN NORTH PENINSULAR FLORIDAAND SOURCE AREAS

Phoebis sennae (Pieridae), Agraulis vanillae (Heliconidae) and Urbanus proteus (Hesperiidae) migrate into peninsular Florida each fall from summer breeding areas throughout the south-eastern United States. Fall flight directions of the three species were studied at 78 sites for c lues to their means of orientation and migratory routes. Mean flight d irections for a visit to a site were calculated using conventional cir cular statistics. The distribution of flight directions permitted usin g linear procedures to combine visit means. The overall mean direction (OMD) of a species at a sire was defined as the mean of visit means, weighted by frequency/angular variance, with a lower limit of 0.2 impo sed on angular variance. In intensive studies at two sites at Gainesvi lle, Florida, mean flight directions during fall migration were largel y independent of rime of day and crosswinds. The OMDs of the three spe cies at the two GainesviUe sites were similar (142 to 156 degrees) and not significantly different among species at a site or, for the same group of dates, between sites for a species. However, day-to-day varia tion among species and between sites was not concordant. Visits to 65 sites on a grid throughout the southeastern United States and to 11 si tes along transects inland from the Gulf and Atlantic coasts yielded 1 0 cases of a P. sennae OMD at a grid or transect site differing signif icantly from its OMD at the main Gainesville site. In each of these, t he OMD was more easterly at sires inland from the Gulf coast or more s outherly or south-westerly at sites inland from the Atlantic coast. By unknown means and with large, unexplained day-to-day variations in di rections, P. sennae converge on peninsular Florida from widespread sum mer breeding grounds. They do this without closely following the Atlan tic or Gulf coasts.