Here I report a unique spiraling flight and orientation behavior (comprising multiple clockwise and counterclockwise circles coupled by extended figure-8 patterns) observed in free-flying “late” migratory monarchs released under sunny ambient field conditions from a location with an unobstructed view of the sky. Following this spiraling flight, migrants continue to fly at very high altitudes until a final orientation and migratory flight direction is established with vanishing bearings statistically concentrated to the SW/W. These results provide preliminary evidence for the possible calibration and use of an inclination magnetic compass that can be used under all local free-flying field conditions. During this spiraling flight, migrating monarch butterflies are proposed to be measuring the direction and inclination of the continuously varying local magnetic field, in a manner analogous to the figure-8 pattern performed to calibrate digital compasses. This behavioral research focuses on the vital pre-migratory orientation and flight behavior that may provide a key behavioral link explaining how migrating monarch butterflies using a time-compensated sun compass system could also integrate the biophysical input from the polarized UV sensitive dorsal rim area (DRA) and the cellular cryptochrome (CRY) system linked to the proposed inclination-based magnetic compass system residing in the distal end of the antennae
