Rb. Srygley, Sexual differences in tailwind drift compensation in Phoebis sennae butterflies (Lepidoptera : Pieridae) migrating over seas, BEH ECOLOGY, 12(5), 2001, pp. 607-611
One prediction derived from optimal migration theory is that migrating anim
als that maximize their flight distance on a given amount of energy will de
crease their airspeed in a tailwind and increase it in a headwind. To test
this in a migrating butterfly, I followed male and female cloudless sulfur
butterflies Phoebis sennae (Pieridae) migrating from Colombia toward Panama
over the Caribbean Sea. P. sennae headed westerly over the Caribbean Sea i
n the morning and then turned southeasterly to head downwind in the afterno
on. Changes in heading and track directions of P. sennae were not related t
o changes in the position of the solar azimuth. As predicted from optimal m
igration theory, flight velocities of females decreased in a tailwind to mi
nimize energy consumption. However, males did not show any compensation for
tail-winds. Females are minimizing energy consumption, whereas males may b
e minimizing the time to reach the destination site in order to maximize ma
tings with newly arrived or newly emerged females. Orientation of females c
hanged before that of males, presumably because their greater reproductive
load imposed greater flight costs and limited flight fuels.