Figure 2

Reproductive migrants show time-compensated sun compass orientation. (A) Vehicle- and methoprene-treated migrants housed under normal fall conditions show a flight orientation in the south/southwesterly direction. Migrants were housed in a light-dark cycle with lights on from 0600 to 1800 hours EST with a temperature cycle of 23°C during light-12°C during dark before being tested outdoors in a flight simulator. The migrants were flown between 1230 and 1530 hours from 19 September to 15 October 2007. The large circles represent the 360° of possible direction (0° = north). The small solid circles on the perimeter represent the mean orientation of individual butterflies. Blue, vehicle-treated migrants; red, methoprene-treated migrants; merge, combined data. The arrow indicates the mean vector, and the length of the arrow represents the strength (r value). (B) Vehicle- and methoprene-treated migrants housed under a 6-hr phase delayed lighting cycle show a flight orientation in the west/northwesterly direction. Migrants were housed in light-dark cycle with lights on from 1200 to 2400 hours EST with a temperature cycle of 23°C during light-12°C during dark before being tested outdoors in a flight simulator. The migrants were flown between 1230 and 1530 hours from 19 September to 15 October 2007. The large circles represent the 360 of possible direction (0° = north). The small solid circles on the perimeter represent the mean orientation of individual butterflies. Blue, vehicle-treated migrants; red, methoprene-treated migrants; merge, combined data. The arrow indicates the mean vector, and the length of the arrow represents the strength (r value).