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.
Douglas, Matthew M.
"Spiraling Flight Behavior May Integrate the Biological Compass Systems of Migratory North American Monarch Butterflies, (Danaus plexippus, L.),"
The Great Lakes Entomologist, vol 54
Available at: https://scholar.valpo.edu/tgle/vol54/iss1/6