Is the Timing, Pace, and Success of the Monarch Migration Associated With Sun Angle?

Monarch butterflies' fall migration to Mexico is influenced by the sun's position, with successful migrants adhering to a 'migration window' defined by the daily maximum vertical angle of the sun (SASN). This study analyzed over 1.38 million tagged monarchs from 1998 to 2015, revealing that those reaching overwintering sites typically migrated within an SASN range of 46° to 57°. The migration follows a slow-fast-slow pattern, consistent with monarchs targeting latitudes with matching SASN. Migration timing may impact population success, as years with low overwintering abundance showed higher late migrant percentages. The findings suggest environmental factors like temperature and daylength interact with SASN to shape migration dynamics.

Taylor, O. R., Lovett, J. P., Gibo, D. L., Weiser, E. L., Thogmartin, W. E., Semmens, D. J., Diffendorfer, J. E., Pleasants, J. M., Pecoraro, S. D., & Grundel, R. (2019). Is the Timing, Pace, and Success of the Monarch Migration Associated With Sun Angle? Frontiers in Ecology and Evolution, 7. https://doi.org/10.3389/fevo.2019.00442